LBT 202 Misfire Diagnostics
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1 P r e s e n t e d b y J i m W i l s o n M I S F I R E D I A G N O S T I C S 1 - 8 0 0 - 7 1 - T R A I N ( 1 - 8 0 0 - 7 1 8 - 7 2 4 6 ) O R w w w . a u t o - v i d e o . c o m D i s c l a i m e r o f W a r r a n t i e s : This manual contains test procedures and test information obtained by an ASE Certified Master Technician with known good test equipment on real vehicles, your tests may vary due to your equipment or technician procedures. No warranty can be made from the ideas presented due to personal testing procedures, nor does the author or anyone connected with him assume responsibilities or liabilities. The use of this manual is conditional on the acceptance of this disclaimer. If the terms of this disclaimer are not acceptable, please return this manual. A u t o m o t i v e V i d e o , I n c . 6 2 8 0 A r c W a y F t . M y e r s , F L 3 3 9 6 6 1 - 8 0 0 - 7 1 - T R A I N ( 1 8 0 0 - 7 1 8 - 7 2 4 6 ) f a x : 1 - 2 3 9 - 5 6 1 - 9 1 1 1 w w w . a u t o - v i d e o . c o m Content authored for Automotive Video Inc. by Heritage Technical LLC, Cochranville, PA. Copyrighted © in 2010 by Heritage Technical LLC. No portion of this manual may be copied, altered, or reproduced without written permission of the author. T A B L E O F C O N T E N T S O V E R V I E W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 C A U S E S O F M I S F I R E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 T Y P E S O F M I S F I R E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 T O O L S F O R F I N D I N G M I S F I R E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Vacuum Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Vacuum Testing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Ford Misfire Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Scan Tool Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Sensors That Can Cause Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Outputs That Can Cause Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Scan Tool History Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Engine Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Cylinder Misfire Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 Misfire Detection Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 GM Misfire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 GM CAM Retard Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Random Misfire Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Lab Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 The Three Sections Of The Secondary Pattern . . . . . . . . . . . . . . . . . . . . . . . . . .13 Firing Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Spark Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Spark Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 Combustion Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Intermediate Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Secondary Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 Ignition Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 Lean Mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 Rich Mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 High Secondary Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 Open Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Intermittent Miss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 Example Of A Lean Cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 Propane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Compression Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Running Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 Technical Service Bulletins (TSBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 C A S E S T U D I E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 0 1998 Oldsmobile Intrigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Rough Idle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 After Complete Fuel Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Cruise After Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Chevrolet Astro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 DTCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 Misfire History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 Firing Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 Exhaust Probe Idle Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 TSBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 Injector Disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 Ignition Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 New Cap And Rotor Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 H A N D S O N T E S T I N G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 Vacuum And Scan Tool Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 Lab Scope Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Transcript of LBT 202 Misfire Diagnostics
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Disclaimer of Warranties:
This manual contains test procedures and test information obtained by an ASE Certified Master Technician with known good testequipment on real vehicles, your tests may vary due to your equipment or technician procedures.
No warranty can be made from the ideas presented due to personal testing procedures, nor does the author or anyone connected withhim assume responsibilities or liabilities. The use of this manual is conditional on the acceptance of this disclaimer. If the terms of thisdisclaimer are not acceptable, please return this manual.
Automotive Video, Inc.6280 Arc Way
Ft. Myers, FL 339661-800-71-TRAIN (1800-718-7246)
fax: 1-239-561-9111www.auto-video.com
Content authored for Automotive Video Inc. by Heritage Technical LLC, Cochranville, PA. Copyrighted © in 2010 by Heritage TechnicalLLC. No portion of this manual may be copied, altered, or reproduced without written permission of the author.
TABLE OF CONTENTSOVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2CAUSES OF MISFIRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2TYPES OF MISFIRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3TOOLS FOR FINDING MISFIRES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Vacuum Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Vacuum Testing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Ford Misfire Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Scan Tool Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Sensors That Can Cause Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Outputs That Can Cause Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Scan Tool History Misfires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Engine Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Cylinder Misfire Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Misfire Detection Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10GM Misfire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10GM CAM Retard Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Random Misfire Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Lab Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12The Three Sections Of The Secondary Pattern . . . . . . . . . . . . . . . . . . . . . . . . . .13Firing Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Spark Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15Spark Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Combustion Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Intermediate Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Secondary Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Ignition Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20Lean Mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Rich Mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22High Secondary Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23Open Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24Intermittent Miss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Example Of A Lean Cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Propane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27Compression Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Running Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Technical Service Bulletins (TSBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29CASE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .301998 Oldsmobile Intrigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Rough Idle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30After Complete Fuel Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Cruise After Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Chevrolet Astro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31DTCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Misfire History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Firing Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Exhaust Probe Idle Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32TSBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32Injector Disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32Ignition Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33New Cap And Rotor Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
HANDS ON TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Vacuum And Scan Tool Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Lab Scope Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Misfires are a very common problem facing technicianstoday. The ability to diagnose what causes misfires andhow to repair them is a valuable skill that you need tobe an effective technician in today's market.
As you can see in the screen capture to the left, not justignition problems can cause misfires.
OVERVIEW
Causes of misfires can be attributed to the Fuel system,Ignition System or the Base Engine(compression/combustion).
General Motors has in fact issued a TSB in relation tothe misfires caused by the fuel system. They are nowrecommending that you add fuel injection cleaner totheir vehicles on a regular basis.
Check with your information provider for moreinformation on this TSB.
CAUSES OF MISFIRES
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TYPES OF MISFIRES
Electrical misfires can be attributed to the spark plugs,wires, cap, coils or a sensor that could be effecting theignition system.
Lean Fuel Charge misfires can be attributed to arestricted fuel injector or a vacuum leak. Runningpropane to the fuel system can help you diagnose aLean Fuel Charge misfire.
Rich Fuel Charge misfires can be attributed to a leakingpressure regulator, injectors or sensors causing toomuch fuel to be introduced into the system. Runningpropane to the fuel system can help you diagnose aLean Fuel Charge misfire.
Density misfires can be attributed to an improper air/fuel ratio mixture in the cylinder. This could be from an EGRproblem, a timing issue or poor compression. Density misfires mimic the same symptoms as a Lean Fuel Chargemisfire, but when you introduce propane in this instance, you will see no reaction and the car will run the same as ifyou had not added propane to the system at all.
Primary Triggering Problems. This type of misfire can be attributed to the Base Engine components such as theCamshaft, timing components or compression issues.
TOOLS FOR FINDING MISFIRES
As you can see there are many tools for finding misfires.Learning to use each one of these will aid in yourdiagnostic strategy.
We will be covering the use of some of these later on inthe hands on portion of this presentation.
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
The new “Buzz” word for the Engine is now “ICE”(Internal Combustion Engine). New name, same thing.
The Engine has been around for a long time and it stillfunctions the same as it has since day one. Yes, enginedesign has changed and variable timing has changedbut the engine is STILL an air pump.
Basic vacuum tests are wonderful for diagnosingmisfires. Introduce propane to the system to see howthe engine reacts.
Vacuum Gauge
Cranking Test: Make sure that the throttle plate isCLOSED. The best way to do this is to disable the fuel.Crank the engine over. You want to see 1”- 5” duringcranking. This will tell you that the engine is in goodshape.
If you see that it is lower, check to make sure that thePCV valve is not stuck open, or for Ford vehicles, theidle air bypass may be stuck open. Either one of thosewill cause a low vacuum.
Warm Engine Test: The vacuum should read 17”-21”steady.
Low Cruise Test: Run this test at approximately 1200rpm - 1500rpm. Anything off of idle. The vacuum should readthe same as idle vacuum, if not higher. If it drops, something has introduced a leak in the system. This is a greattest to diagnose an off idle hesitation condition.
High Cruise Test: Again, make sure that you maintain the same vacuum specifications you did at idle. Make sure toleave the engine running steady for at least 1 minute. If you are running this test and the vacuum starts to drop,this could indicate a restricted exhaust system or the EGR just activated. Disable the EGR and run the test again.
Snap Test: From idle, USE YOUR HAND to snap the throttle to WIDE OPEN. The vacuum should drop to below 5” oras close to 0” as you can get. It should rebound to 3”-5” higher than idle vacuum.
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Many Technicians are now using Mode $06 in theirdiagnostic strategies. Mode $06 will give you misfirecounts per cylinder on Ford products.
You can see in the screen capture that we are looking atTest ID 53, Component ID: 05. The measured value ofmisfires is 109 which is well below the maximum limitof 13,568. Therefore, the result is a “Passed” value.
Scan Tool
This is good information, but you still need to know how and why the misfire occurred. Go to motorcraft.com andresearch the OBDII Theory and Guide in the Technical Resources section of the website for more information.
Above is a screen capture of what a typical Ford Misfire Data chart looks like. All of these are vehicle specific andgive you great information on how misfires happen and what causes them for the vehicle that you are working on.
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Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Above is a screen capture of the J1979 Misfire Mode $06 Data sheet. This particular chart is for a later Fordvehicle and the test ID is $53. The test description is Cylinder specific misfire and catalyst damage thresholdmisfire rate (either cat damage or emission threshold)(updated when DTC set or clears). In this instance, you mayneed to clear DTCs and re-test to see if there is a problem.
CAN compliant vehicles show the misfires for the last drive cycle or the exponentially weighted moving average forthe last 10 drive cycles. All vehicles that are CAN compliant will be giving you this information.
At the bottom you can see the conversion test. This conversion test will give you the percentage of misfires. Youmay have a vehicle with a percentage of misfires that can pass the test, but it is a good idea to repair the misfireanyway and keep the customer happy.
Scan Tool
7
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Mass Air Flow Sensor: A MAF Sensor that is eitheroverestimating or underestimating air flow can cause amisfire condition.
Manifold Air Pressure: A defective MAP sensor cancause a misfire condition.
Throttle Position Sensor: Rare but it does happen. Adefective or an incorrectly calibrated TPS can cause amisfire condition.
Air Charge Temperature Sensor: If the sensor believesthat it is running too hot or too lean, it will effect theair/fuel mixture of the vehicle causing a misfirecondition.
Crankshaft Position Sensor: Defective or improperly working CKP sensors can cause a misfire condition.
Camshaft Position Sensor: Defective or improperly working CMP sensors can cause a misfire condition.
Scan Tool
Exhaust Gas Recirculation, Ignition Control Modules,Fuel Pumps and Injectors ALL can play a big part incausing misfires.
An example could be a weak fuel pump that will makethe car run lean. Restricted injectors can cause thevehicle to run lean resulting in a misfire as well.
All you need is one cylinder that is running lean. The O2sensor is going to see the engine running lean, it willincrease fuel to the system to try and correct theproblem. As a result, the one cylinder that was runninglean has now been corrected, but the other cylinders arenow running too rich which can result in a misfirecondition.
8
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Misfires in Scan Tool History. Looking at the screencapture we see a couple things. First you can see theMisfire Current for Cylinders 3, 4, 5 & 6, all of whichhave a misfire count of 0.
Below that is the Misfire History Count for Cylinders 1 -6. The cylinder with the biggest misfire history iscylinder #3 with 548 misfires.
Address your diagnostic testing starting with thecylinder with the highest number of misfires and workyour way down to the cylinder with the lowest number ofmisfires.
Scan Tool
RPM Input Testing. Use the RPM pattern for testing for aglitch, injector and symptom based diagnostics oferratic idle speed or injector pulse loss under load.
You want to make sure that your RPM is steady. Checkthe vehicle at idle and make sure that you are within +/-20RPM of the target idle speed. If you have an idle thatis higher than that, check for things like a faulty sensoror a worn base engine component.
9
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Engine Condition. Graph MAP and RPM together. Thetrick to doing this is to select the minimum amount ofPIDs that you need to view. The datastream is updatedquicker and more accurate with the less amount of PIDsyou want displayed.
Less data (PIDs) = more accurate readings.
If the MAP is steady but the RPM is erratic, this indicatesan ignition or fuel related problem, if the MAP and RPMare both erratic, this indicates that a mechanical issue islikely the cause.
Scan Tool
Cylinder Misfire Testing. Another good use of the scantool is Cylinder Misfire Testing. Connect the scan tool tothe vehicle, graph and record the rear (post) HO2 Sensor,and drive the vehicle with the engine at operatingtemperature and cruising speed. Record the base linevoltage.
If the voltage goes high, this indicates a secondaryignition misfire. If the voltage drops low, this indicates alean injector misfire or a fuel delivery problem.
This a good test to determine a transmission problem aswell. If the vehicle is displaying a misfire condition butthe post O2 sensor is within the normal range, this couldindicate a torque converter problem.
10
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Misfire Detection Limits. Not all cars have full rangemisfires. Earlier GM, Ford and Chrysler vehicles hadmisfires that did not go full range. Chrysler went up to1,440 RPM and GM went to about 2,500 RPM. In 1999all manufacturers were required to have full rangemisfires..
Diesel engines such as the Power Stroke and Duramaxwill only find misfires at less than 750 RPM. This meansthat above 750 RPM, the system shuts off the misfirecounter.
Scan Tool
As we all know by now, GM has had a lot of problemswith Caps and Rotors causing misfire conditions. Thereare a fair amount of TSBs related to this matter that GMhas released.
Make sure that when you are doing a Crank Position Re-Learn that you have put the components in the correctposition to avoid further misfires.
TOOLS FOR FINDING MISFIRES
11
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
GM CAM Retard Tests. The spec is 0 degrees +/- 2degrees for V8 engines. Monitor the PID with the engineat normal operating temperature. Raise the RPM to1000 RPM after adjusting the distributor to force thecomputer to recalculate CAM Retard PID.
Repeat these steps until the PID indicates 0 degrees.
Scan Tool
TOOLS FOR FINDING MISFIRES
Random Misfire Testing. Check for ignition timingchange in relationship to temperature. The scan toolPID for spark advance should be checked in response toTPS/RPM input. These should be moving in relationshipto each other.
You can see that at 1,976 RPM the timing is at 40degrees timing advance. Later in the datastream youcan see that the instructor did a snap throttle to about4400 RPM and the timing decreases.
If the engine is cold, you should have more timingadvance. If the engine is warm, you should have less.Using this data you can diagnose a system that mayhave a misfire condition.
12
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
The Lab Scope indicates the types of misfires withindicating lines. Electrical misfires are found in thefiring line, Lean Fuel Charge, Rich Fuel Charge andDensity misfires are all found on the Burn KV line. APrimary Miss-Triggering Misfire will be in the CoilCharge/Dwell section.
Lab Scope
TOOLS FOR FINDING MISFIRES
13
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
The above screen capture shows the Three Sections of the Secondary Ignition Pattern. Section “A” is the firingsection where the work is being done. Section “B” is the intermediate section where the ignition coil is dischargingback to ground. Section “C” is the dwell section where the coil is being charged back up. Keep in mind that all ofthis is happening very fast at around 7 milliseconds.
We will take a closer look at all of these on the next few pages.
Lab Scope
TOOLS FOR FINDING MISFIRES
NOTES
14
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
The Firing Line is the amount of voltage required to ionize the spark plug gap (between 10kV - 15 kV). There shouldbe no more that 3kV - 5kV variation between cylinders. If there is more than 3kV - 5kV between cylinders OR areading above 15kV, you have a problem. This could indicate such things as worn plugs or bad wires.
You will however have some variation between cylinders at idle. Remember, you have a different air/fuel ratio atidle and this will effect the firing kV.
NOTES
15
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
The Spark Line is the intersection on the pattern that indicates the amount of voltage needed to maintain a sparkacross the gap. On a distributor type ignition it is at about 1.5kV - 2.5kV. Anything more than that and you would belooking for a resistance problem. Anything below is indicating a ground problem.
On a DIS equipped vehicle there is a little bit of a difference. You should be looking at a maximum of 4.0kV on awaste spark and when you are in compression it should kick up to about 10 kV.
NOTES
16
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
Spark Duration is the amount of time that the spark jumps across the gap. Most DIS equipped vehicles will have aspark duration of 1.3ms - 1.5ms. You really want a minimum of 1.0ms burn time on a DIS vehicle. If you do a snapthrottle test and the spark duration drops low, you have a problem.
The spark duration is effected by compression and fuel mixture. If you were to break the burn duration time in halfand look at the pattern to the left where the firing kV is, this is external to the cylinder. This can indicate problemsin the wires, cap, rotor and plugs etc. The other side of the pattern is what is occurring inside of the cylinder. Thisindicates problems with things such as air/fuel mixture, lean and rich conditions, carbon and EGR problems etc.
NOTES
17
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
Above is an older picture of a Combustion Chamber but is still accurate. As the air/fuel mixture begins to go acrossthe spark plug gap in a lean condition (B) the pattern moves up. Conversely, during a rich condition (A) the patternis moving down. This will vary ever so slightly as the pattern moves across the screen.
NOTES
18
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
The Intermediate Section indicates coil oscillation. You want to see 3.0kV - 5.0kV on the older models with aminimum of 1.0kV.
NOTES
19
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
Secondary Tracking will usually show up in short downward positive spikes. Notice the difference between thepattern on the coil section in the previous screen capture and the secondary tracking screen capture above. Noticethat is not the uniform cone shape pattern but short downward spikes. This indicates a coil problem and it mayneed to be replaced.
NOTES
20
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
Keep in mind that you only have so much coil activity. If you are using a lot firing kV, your burn time will shorten. Ifyou are using less firing kV your burn time will increase. If you use up all of the energy to initialize the plug, youdon’t have enough to maintain the spark across the gap which can cause a misfire.
NOTES
21
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
TOOLS FOR FINDING MISFIRES
Above is a capture of a Lean condition. Notice that the pattern started out normal but at about half way through itstarts to rise up. This indicates a lean condition in the cylinder. If the cylinder is running out of fuel molecules, thiswill require the voltage to increase resultin in a higher voltage requirement.
Note that this same type of pattern will show up if you have an EGR that is stuck open. If you were to run propane tothis lean condition cylinder, the pattern will decrease and go back to near normal. If you run propane to thiscylinder and it has an EGR problem, you would see no improvement or effect on the cylinder at all.
NOTES
22
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
A Rich Mixture condition pattern will do the opposite of a Lean Mixture condition pattern. It will start high andtrend downward. There is a lot of fuel in the cylinder and it requires less energy to ignite it therefore the voltagerequirements will drop.
NOTES
TOOLS FOR FINDING MISFIRES
23
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
If the firing line is high, and the burn line is high, you have a secondary resistance problem. This could indicateproblems with the Distributor Cap, Rotor, Wires..etc. If all cylinders are showing this pattern, you are looking atCap, Rotor or Coil wire. If only one cylinder is displaying this pattern, you need to look for individual resistance thatwould be effecting just that cylinder.
NOTES
TOOLS FOR FINDING MISFIRES
24
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
Notice that an open circuit has no burn time. This is because all of the energy has been used up to jump the gapand none is left over to maintain the spark. This is a misfire.
NOTES
TOOLS FOR FINDING MISFIRES
25
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
By looking at an Intermittent Miss pattern you can see that the pattern is jumping up and down.
NOTES
TOOLS FOR FINDING MISFIRES
26
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Lab Scope
Above is an example of a lean cylinder. Notice that we are barely maintaining 1millisecond per division and 1kV perdivision. Also note that the resistance jumps are caused by the lean condition. Propane was introduced into thesystem and the ignition pattern returned to normal.
Also notice the waste spark pattern at the bottom has not been effected because we are not on compression, butexhaust.
NOTES
TOOLS FOR FINDING MISFIRES
27
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
Propane
As discussed earlier, the use of propane is a great way to identify lean or rich running conditions. If you addpropane to a running engine and the RPM drops, this indicates that the system was running rich to begin with. Ifyou add propane to a running engine and the RPM increases, this indicates a lean condition that could be causedby a vacuum leak, fuel restriction, etc. If you slowly add propane to a running engine and the RPM slowly drops,and the engine compensates by increasing the RPM, this indicates that the engine was probably running normalbefore you even started.
If you consider using propane in your diagnostic strategy, use a metering gauge to see exactly how much propaneyou are adding.
TOOLS FOR FINDING MISFIRES
Compression Gauge
A fair amount of technicians shy away from the use ofcompression gauges. Compression tests require theengine to be at normal operating temperature andsome engines, like the Ford V10, are difficult to get tothat temperature and maintain it during the test.
A good test is a Cranking Compression Test. Disable thefuel or ignition or both on the vehicle and the throttleplate must be open.
The first pulse on the gauge MUST be 50% of the finalpressure. If it isn’t, this could indicate a worn cylinder orworn piston ring. The second pulse should be 90% ofthe final pressure with four pulses total.
While this is a good test to tell you if the system issealing during cranking, it does not tell you if thesystem is sealing at idle.
Leave the gauge attached to the suspected cylinder andrun the engine at idle. The pressure should rangearound 50 to 70% of the cranking pressure. Snap thethrottle, (using the throttle plate not the accelerator), totest volumetric efficiency. You should be within 80% ofthe cranking pressure during the snap throttle. If not,this indicates you have a problem.
28
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Compression Gauge
Using the equation to the left, this engine should be at50psi at idle. Remember to use the throttle plate to dothe snap throttle and NOT the accelerator pedal.
This screen capture shows what a Running CompressionNormal Readings should look like. Note that the snapthrottle readings are 50 psi higher than the running idlevalue
Notice in this screen capture that the snap throttlevalue for cylinder number 1 is barely above the runningidle value. This indicates a restricted intake. This couldbe caused by a multitude of problems but it gives you agood starting point for your diagnostic strategy.
29
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
TOOLS FOR FINDING MISFIRES
Compression Gauge
Note in this screen capture that the snap throttle valueis 180 for cylinder number 1 which is way above therunning idle value of 75. This high of a value indicates arestricted exhaust problem.
Since all of the other cylinders have normal values, thiscannot be a restricted exhaust system.
Technical Service Bulletins (TSBs)
Search the TSBs for the vehicle that you are working on. Some may require a reflash of the PCM and some mayrequire components to be replaced. Some may require both.
Reflashes can be required if the parameters on the vehicle are too narrow. The reflash will widen those parametersand solve the problem.
NOTES
30
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
CASE STUDIES
1998 Oldsmobile Intrigue
The customer complaint on this vehicle was a roughidle. The idle is running between 707 RPM and 754RPM. The MAP sensor is running at about 11 inHg partof the time and 10 inHG the rest of the time meaningthe vehicle is losing 1 inHg of vacuum regularly.
Also, the vehicle had a real problem maintaining a 1millisecond burn time and the ignition pattern indicateda lean running condition.
After a complete fuel system service of cleaning theinjectors on the vehicle, de-carboning the engine, andcleaning the MAF, the engine is idling better and thereis no change in the MAP sensor readings.
The Cruise after Cleaning shows that everything is reallylooking better now. This fuel system service on thisvehicle cured the misfire condition and cleared the DTC.
31
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
CASE STUDIES
Chevrolet Astro
Here we have a Chevrolet Astro with three DTCs found.P0102B, P0300B and P0453B, The P0102B and theP0453B have already been repaired and we will focuson the P0300B misfire code.
Keep in mind that all of these are “B” codes which aretwo trip codes. “A” codes are single trip codes that candamage the Catalytic converter and the “B” codes arenot as damaging to the system.
The screen capture to the right shows the misfire historyfor this particular vehicle. You can see that Cylinder #3has a history of 548 misfires. Remember, start with thecylinder that has the highest number of misfires thenwork your way down.
Check the firing order. This will tell you where themisfiring cylinders are in the firing sequence.
32
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
CASE STUDIES
Chevrolet Astro
This is a screen capture of the idle reading wavepatterns using an exhaust probe. Normally thesepatterns would be fairly uniform in appearance. Thispattern shows two patterns that do repeat but the restof the pattern does not.
Search the TSB library and see if there are any TSBsthat relate to the vehicle you are working on and theproblem that you have with the vehicle.
It just so happens that there was a TSB relating to thesubject vehicle with a Fuel problem.
To verify that this was actually a fuel related problem,the instructor disabled the number 3 injector. Noticethat the RPM has dropped to approximately 562 RPMfrom approximately 617 RPM and the O2 Sensor wentto a lean condition.
This means that fuel was being delivered to the cylinderand this rules out the fuel problem and is pointing moretowards an ignition problem.
33
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
CASE STUDIES
Chevrolet Astro
To the right is a lab scope screen capture of the ignitionpatterns for this vehicle. As you can see, there is highresistance on all but one cylinder which means theproblem is common to the entire engine.
Note the arrow on the right side of the screen capture.All of these cylinders are running at more than 4kV.Again, this indicates a high resistance that is commonto all of the cylinders in the engine.
This lab scope pattern shows what the ignition patternslook like after a new cap and rotor have been installedon the vehicle. Note that the pattern is much morestable but is still not quite correct.
The vehicle still needs a set of spark plugs and maybewires but the cap and rotor was common to all of thecylinders and replacing it was a good start.
The firing kV dropped from 27.2 to 12.3 which solvedthe misfire and rough idle.
34
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
HANDS ON
Vacuum and Scan Tool Testing
Remember that when you do vacuum testing you wantto start out with a Cranking Vacuum Test. You need todisable either the ignition system or the fuel system. itis easier to disable the fuel system by removing the fuelpump relay from the vehicle.
You want to see a fairly steady reading on the gaugeand you need to pull at least 2” of vacuum duringcranking. This vehicle was pulling around 2.5” andpassed the cranking vacuum test.
35
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
HANDS ON
Vacuum and Scan Tool Testing
Using a scan tool, we will demonstrate how to use the MAPsensor like a vacuum gauge in the previous crankingvacuum test.
Set up your scan tool in custom data stream to only viewthe PIDs that you need for this test. By doing this, thespeed of the data will be faster and provide you with amore accurate reading.
The instructor has set up a Genisys to view only the MAPinHg and the MAP Volts and has started the crankingvacuum test.
The test started at about 28 inHg and at about 4.8 Volts.As the engine was cranking, the MAP inHg fell to 28 and the volts dropped to 4.4. This indicates a 2” drop invacuum which is the same 2” of vacuum that was viewed in the test using the vacuum gauge. This shows that theengine has good volumetric efficiency and is breathing well.
The instructor replaced the fuel pump relay and beganan Idle Vacuum Test. You can see that the vacuum isjust under 20”. This indicates a fairly good runningengine at idle.
36
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
HANDS ON
During the Cruise Vacuum Test, we reached an RPM ofabout 2,464 and picked up an additional 1” of vacuum.Again, this portion of testing is indicating that theengine is running fine.
Vacuum and Scan Tool Testing
The above screen captures demonstrate what you should see during a Snap Throttle Vacuum Test. The capture tothe right shows the vacuum dropping to almost 0” when the throttle is first snapped. The vacuum then increases toalmost 25” as the engine reacts to the snapping of the throttle, then dropped back to its original value of 18”.
Mechanically this engine is in very good shape. This does not mean that there are no other problems with thevehicle. There may be other things such as fuel or ignition problems but the base engine appears to be in goodcondition.
37
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
HANDS ON
The instructor has adjusted the custom datastream tonow include Engine Speed (RPM). The RPM has beenincreased to 1216 RPM and the MAP reading continuesto get more stable at around 10 inHg.
Vacuum and Scan Tool Testing
The instructor has adjusted the custom datastream tonow include Engine Speed (RPM). The RPM has beenincreased to 1216 RPM and the MAP reading continuesto get more stable at around 10 inHg.
As the engine RPM is increased you will see that thevoltage pattern stays pretty good and the MAP patternstays pretty good. Remember that you will always havesome variations in the patterns and that this is normal.
During the Snap Throttle Vacuum Test you can see thatthe RPM reached 3,928 RPM, the MAP inHg reached ahigh of 29 and the MAP Volts reached a high of 4.6.
As the engine returned to idle, all of the values returnedto normal. This test also confirms what was previouslydemonstrated in the vacuum gauge test. This is amechanically sound engine and our problem is either fuelor ignition related.
38
Presented by Jim WilsonMISFIRE DIAGNOSTICS
1-800-71-TRAIN (1-800-718-7246) OR www.auto-video.com
As discussed earlier, you want to be between 5 kV - 15 kVwith a burn time of about 1 millisecond. The pattern showsthat the Peak kV is running at 8.5 kV and the the burn time isaround 1.274 milliseconds.
This indicates that the ignition system on this cylinder isrunning pretty close to optimal.
Test each cylinder sequentially and compare your results. Thiswill tell you if there are cylinders that could have a fuelproblem or have an ignition problem.
Lab Scope Testing
HANDS ON
