BOSCH D JETRONIC Fuel Injection of Renault 17 TS

7/28/2019 BOSCH D JETRONIC Fuel Injection of Renault 17 TS

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The BOSCH D JETRONIC fuel injection of Renault 17 TS

The fuelinjection of Renault 17 TS was designed by Bosch and it was used by someother car makes as well. So it might be easier to find sare parts to the fuel injectionfrom a Bosch dealer, I have made this translation list so it is possible to get the Bosch

part numbers. But if you are having problems with your fuel injection such as lack ofpower in high revs always start with replacing the fuelfilter, another thing to start withmight be to add some kind of fuel injection cleaner. Another fuel injection tip is to addsome twostroke oil to the petrol everytime you fill the tank, this oil makes the lifeeasier for the electric fuelpump.

This scematic drawing shows the indexes from the table below.

BOSCH D JETRONIC PART NUMBERS (R1313 R1323)Index on drawing Name Bosch part number Renault part number

1 Electric fuelpump 0 580 960 007 77 00 557 763

2 Fuel filter ?? 77 00 545 787

3 Pressure regulator 0 280 160 001 77 00 545 780

4 Fuel injector 0 280 150 016 77 00 545784

5 Cold start injector 0 280 170 013 77 00 545 782


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6 Distributor JFUX 4 0 231 163 064 77 00 577 336

7 Pessure sensor 0 280 100 031 77 00 545 776

8 Auxiliary air conrol 0 280 140 019 77 00 545 783

9 Throttle switch 0 280 120 011 77 00 569 162

10 Air temperature sensor 0 280 130 016 77 00 545 778

11 Coolant temperature sensor 0 280 130 014 77 00 545 779

12 Temperature time switch 0 280 130 201 77 00 556 448

13 Ignition / starter switch -- 77 00 534 018

14 Control box 0 280 000 025 77 00 545 851

15 Main relay -- 77 00 545 853

16 Pump relay -- 77 00 545 853

17Auxiliary air vaccum valve (just on some

models)

0 280 160 106 77 00 556 449

The Renault 17 TS Bosch fuel injection system.


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D Jetronic Fuel Injection - Mercedes Benz Tech Tips

D Jetronic Fuel Injection Tech Tips 1971 to 1976

The D Jetronic system was introduced in 1967 and started appearing widespread in Volkswagens.

Sensors constantly sense the operating conditions of the engine and transmit signals to an electrical

control unit.

When and how much fuel injected into the engine, is calculated on intake manifold pressure and

engine speed. The most critical measure is intake manifold pressure. For the trivia nuts, D, the firstletter of D Jetronic is also the first letter of the German word Druck that means pressure

The D Jetronic system relies on constant fuel pressure if the electronic control unit is to deliver theprecise amount of fuel during different operating conditions. To achieve this constant pressure the fuel

pump needs to be able to deliver more fuel than the engine will ever require thus the pressure can beregulated by re-circulating the excess fuel back to the fuel tank.

First we will list a brief description of each part, followed by their operation with a few little tips we

have picked up along the way.

Electric Fuel Pump

The fuel pump is a roller type electric fuel pump, which delivers fuel under pressure in a closed

system. The closed system consists of a pipeline to a fuel rail, which contains solenoid-operatedinjectors a fuel pressure regulator and a fuel return line to the fuel tank. The fuel pump also contains a

one-way check valve, or non-return valve, in it's outlet to prevent fuel flowing backward and maintainpressure in the system after shutoff.

Fuel Pressure Regulator

Since the fuel pump delivers more pressure than the maximum requirement of the engine the fuelpressure must be regulated. It is this constant fuel pressure, which enables the electronic control unit

to deliver the precise amount of fuel.The fuel pressure regulator, located at the back of the fuel rail, consists of spring-loaded diaphragm ina steel housing. When fuel pressure overcomes spring pressure the valve opens and fuel is divertedback to the tank thus maintaining a constant pressure. The spring pressure is adjustable by turning an

adjustment screw which increases or decreases spring pressure and consequently increases ordecreases fuel pressure. Fuel pressure is normally 28 to 30 lbs. in the fuel rail. Check the service

manual for your pressure setting.

Fuel Filter


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Filters out the impurities of the fuel to protect the fuel system components.

Electronic Control Unit (ECU)

The electronic control unit back then was an analog control unit. Transistors still weren't cheap then as

those of you who owned and listened to their transistor radio can attest to. Remember them?The electrical control unit receives inputs from various sensors and determines the amount of fuel theengine requires to operating conditions. It controls the fuel flow by controlling how long the electronic

injector valves remain open.

Mercedes Benz Tech Tips - D Jetronic Fuel Injection

Electronic Fuel Injector

The fuel injector is an electric solenoid operated valve. The electronic control unit sends electricalpulses to the fuel injector, which energizes the solenoid and results in fuel, which is under pressure,

being injected in front of the intake valve.

Cold Start Valve

A cold engine causes fuel to condense on the cylinder walls and in the intake manifold. The end result isthat fuel that is condensed does not mix well with the incoming air and is extremely hard to ignite. The

solution was the cold start valve. The cold start valve is designed to inject atomized fuel near the air

inlet thus creating an ignitable mixture. The cold start valve only operates when the starter is engaged

Thermo Time Switch

The thermo time switch opens and closes the current that flows to the cold start valve depending on

the temperature of the engine. The design and operation is simple.


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Inside the thermal time switch is a strip of bimetallic metal connected to one terminal of the sensor.

Heating windings surround this bimetallic strip. When the engine is cold the bimetallic strip contactsthe strip that the other terminal is connected to. Picture a set of ignition points. When it is cold the

points are closed and when the engine is warm the points are open.

This construction enables the thermo time switch to control how long current is supplied to the cold

start valve. When the starter is engaged current flows through the heating windings heating thebimetallic strip of the thermo time switch. As the bimetallic strip heats up it spreads the contacts and

the connection is lost with the other terminal which cuts off the current to the cold start valve.Therefore the colder the bimetallic strip is, the longer time it takes to spread the terminals and the

longer time the cold start valve receives current and remains activated. This time interval can be asshort as 1 second or up to 20 seconds when the temperature is -20 degrees Celsius. Remember the

cold start valve only works when the starter is engaged.

Temperature Sensors

There are a few temperature sensors located throughout the engine compartment. The hollow

threaded sensors contain a semiconductor material whose resistance decreases as the temperatureincreases.One sensor measures the temperature of the coolant while the other sensor or sensors measure the

temperature of the air. A cold engine requires more fuel than a engine at operating temperature sinceit must overcome additional friction and the effects of fuel condensation. The electronic control unit

constantly monitors the resistance values of these sensors. The electronic control unit uses theseresistance values to calculate the proper amount of fuel to be injected based on coolant and air

temperature.

Auxiliary Air Valve

As we have stated above, a cold engine requires more fuel than a warm one to overcome additional

friction and combustion deficiency. A cold engine also needs to produce more torque. The extra torque

is achieved by the introduction of more air into the engine. Not only does this increase the idle speedslightly, the electronic control unit will react to this additional air by injecting an additional amount of

fuel. Thus the requirement of extra torque and extra air and fuel is met.

They're a few different styles of auxiliary air valve but they essentially perform the same function,which is the introduction of additional air behind the throttle plate. The size of the opening in the

auxiliary air valve is determined by temperature. The colder it is, the larger the opening that will beuncovered inside the auxiliary valve. The larger the opening uncovered inside the auxiliary air valve

the more bypassed air flows behind the throttle plate. The opening in the auxiliary air valve will beslowly reduced and the temperature rises and will close at operating temperature, at which time

bypassed air will not flow behind the throttle plate through the auxiliary valve.


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The two most common types you will see are the electrically heated bimetallic type and the wax pellet

type, which is immersed in engine coolant.

Trigger Contacts

Trigger contacts, also referred to as trigger points, are housed in the lower section of the ignitiondistributor underneath the mechanical centrifugal advance plates. The opening and closing of thetrigger contacts indicate the speed of the engine since the ECU monitors the interval of time between

trigger pulses.

Tech Tipthe trigger contacts signal the "start" of injection while the "duration" of injection, which ishow long the injectors remain open, is determined by the inputs of the pressure sensor, engine speed,

and the various other engine sensors to the electronic time switch of the ECU.

The trigger points, on a V8 engine contain four sets of points. The trigger points are not that dissimilar

from ignition points in looks except they do not carry voltage. As each set of points is opened andclosed the ECU knows when to fire each set of corresponding injectors based on crankshaft position.

Since the distributor is installed at top dead center, the trigger points corresponding lobes inside thedistributor correlate to the position of the crankshaft. Consequently the injectors are pulsed at the

precise time.

Throttle Switch

The throttle switch, in a pressure type system, is used to bridge the gap or time delay between the

time intake pressure signals the ECU for an increase in fuel versus the immediate call for fuel when thethrottle plate is opened. The throttle switch performs the same function as the accelerator pump does

on a vehicle equipped with a conventional carburetor.The throttle switch is connected directly to the throttle plate. It consists of two contact arms, which

slide or sweep across a graduated zigzag contact path. This zigzag pattern allows the ECU to receivesignals as the contact arm sweeps up that the throttle is being depressed and therefore enrich the

fuel. One contact path is used for acceleration while the other contact path is contains a full load and

an idle contact.

Pressure Sensor

The pressure sensor is the most critical sensor in the D Jetronic system. The pressure sensor is housed

in a metal housing and contains two diaphragm cells, which displace an armature that is inside a coil.When the armature is moved inside the coil, the inductance of the coil changes Therefore, the pressure

sensor converts a pneumatic signal into an electrical signal which the ECU can measure and determinethe correct duration of the injector pulses.


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One chamber of the pressure sensor is at atmospheric pressure while the other is at intake manifold

pressure since a vacuum line is connected from the intake manifold to the pressure sensor. Thedifference between these two pressures will cause the armature to move within the coil changing the

induction of the coil. The resulting electrical value that the ECU receives will determine the load of theengine and consequently the amount of fuel to be injected. Pretty trick for the late sixties.

Series Resistors

Some D Jetronic systems use a set of resistors to drop the voltage to the injectors. We have rarelyseen these fail.

Refer To Your Service Manual For Your Car.

You must use extreme caution when working with gasoline because of the extreme risk of fire and

injury. Follow the procedures in the genuine Mercedes Benz service manualfor your car. The textbelow is general knowledge and is not meant to take the place of the service procedures that your

manufacturer recommends. Many different vehicles have different versions of the D Jetronic systemand different procedures may apply. the starter is engaged.

Working With D Jetronic

We cannot empathize more the importance of doing all the basics first before beginning to diagnose a

fuel injection problem.

Rule number 1do not assume it is a fuel injection problem.

Rule number 2read rule 1 again

Before you start you must have fresh fuel. If the vehicle has been sitting for a prolonged period of time

the fuel must be drained, the fuel filter changed, and possibly the fuel tank cleaned.


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You must make sure your ignition points are in good condition and that you have checked your dwell

and timing and that the rubbing block of the points is lubricated. So many people drop the ball here. Inormally just pop a new set of points in just to eliminate any doubt.

Make sure your centrifugal advance is free and lubricate if possible. Some of the distributors have a

wick under the rotor where you can apply a couple of drops of oil. While you are right there check your

vacuum advance too.

Make sure all of your maintenance has been done such as distributor cap, rotor, air filter, fuel filter and

oil change. If your car is running super rich, black smoke, you may need to change your oil again eventhough it may have been just done recently.

You must also make sure your spark plugs are new and your ignition wires are good. Visually take outeach spark plug and check to make sure each plug is firing and free of deposits. The plugs should be

tan in color and be free of carbon deposits. Check the spark plug gap. If the gap is higher than specyou will probably see the electrodes are rounded and the plugs are need of replacement. Before you

put the spark plugs back in test the compression. See your service manual for procedures andspecifications. The compression must meet specifications or the fuel injection system will not work

correctly.

Remember the pressure sensor monitors intake manifold pressure. The engine must be in goodmechanical condition if it is to work correctly.

Do not assume any of the parts are good. Don't guesstest! Check and repair as necessary beforeproceeding. If you skip the above steps you are very likely not to diagnose the problem correctly and

buy a part that you did not need. Examples of this are changing your fuel pump because of a cloggedfuel filter, changing the control unit over a set of points, etc., etc., etc.

The next step is to perform a visual check of all vacuum lines and replace all that are cracked, spongy,or rock hard. If they have never been changed before now is the time since a couple of decades have

taken its toll. If you need to change any of the vacuum lines, we recommend using the German linewith the cloth braid. Any vacuum leaks will surely cause drivability problems since the pressure sensor

will report inaccurate readings to the ECU.

Make sure you check all of your fuel lines for cracks and any other signs of deterioration, which can

cause a fuel leak. The rubber fuel lines should not be hard. Check all the clamps and make sure theyare tight. You should not see any evidence of the hose clamp cutting into the hose or a swelling or

mushrooming next to the clamp.


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If you are going to change any fuel line you must use fuel line that is designed for fuel injection and

can withstand the high pressure. You must use a clamp that is designed for fuel injection. These aresmooth on the underside and will not cut into the hose. The cheap screw type clamps, not designed for

fuel injection, will actually cut through the fuel hose over time. Failure to use the wrong type of fuelhose or hose clamp will result in a rupture and a fuel leak, which may result in a severe engine fire.

Believe it or not, the majority of you have probably found and repaired your problem after followingthe steps above. If you are still experiencing problems now we can start to look for a possible fuel

injection problem

Check All The Connectors And Connections

The first step is to remove the air cleaner assembly and check all of the connectors and connections ofall sensors and injectors. Over time the rubber boots may have deteriorated and may have led to a

corrosion problem. Remember the connectors back then were not very weather resistant so you shouldremove each connector and check for corrosion and pull back the boot and check for broken wires and

corrosion. The wires sometimes get so brittle from being baked for two decades that they may havebroken. Also be sure to check the wiring for any broken insulation

Another cause for injection problems and driveability problems are bad grounds caused by corrosion.

These grounds are usually comprised of multiple wires bolted to the intake manifold or engine.

Test Fuel Pressure

The next step is to check your fuel pressure in the fuel rail. This can be checked using a fuel gauge

designed for testing fuel injection. The fuel pump is capable of delivering more fuel and pressure thanis required to run the vehicle at all operating conditions. As was mentioned earlier, the fuel pressure

regulator bypasses this excess fuel and pressure and returns it to the tank.

We are interested in checking the pressure in the fuel rail. This pressure must be constant since theelectronic control unit's calculation of the duration of injector opening is based on constant fuel

pressure. If the pressure were allowed to vary in this system there would be no way to control the

amount of fuel being injected. For example, if you had one fuel injector connected to a source of fuelat 20 pounds per square inch and opened the injector for 10 milliseconds less fuel would flow from thatinjector than if you had a similar injector connected to a source of fuel at 30 pounds per square inch.

More pressure more fuel.

To check the pressure in the fuel rail disconnect the fuel hose from the cold start valve and connect

your fuel pressure gauge to the hose to the hose. Cycle the ignition key a few times and check for anyfuel leaks. While you are cycling the key check the pressure. The pressure varies between vehicle

applications but a rule of thumb is 28 to 30 pounds per square inch. If your vehicle runs then start the


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engine and check the fuel pressure. If the pressure does not meet specification it may be adjusted by

loosening the lock nut on the fuel pressure regulator and rotate the adjusting screw in or out until youreach the proper pressure. Turning the screw in raises pressure and out lowers pressure. Be sure to

re-torque the lock nut after setting the pressure. If you do not have fuel pressure, read on and thistopic will be discussed under the topic no start.

If you cannot obtain high enough fuel pressure to meet the specification, then your fuel pump or fuelpressure regulator is defective. We already know your fuel filter is good since you did the maintenance

above before checking for an injection problem.

Shut the engine off and note the pressure. The pressure should not fall to 0 instantly. Pressure should

be maintained in the rail after shut off. This is called rest pressure. If the correct pressure ismaintained for the specified time you can now ignore any further text dealing with rest pressure since

you just tested it. For those of you who failed, we will discuss some of the drivability problemsassociated with loss of rest pressure.

Tech TipIf you are going to buy a gauge set; buy the gauge set that also adapts to check K and KECIS systems and L Jetronic systems. This way you can check the fuel systems of most European

vehicles.

The Basics Are Done

We have now done all the work that was necessary before we can start to look for problems with our D

Jetronic system. We have done all the maintenance, checked compression, checked all the vacuumand fuel lines, checked all of our connections, and we know we have the correct fuel pressure. We now

have the platform where the ECU can effectively run the vehicle.

Problem By Symptom

This section is only concerned with D Jetronic fuel injection and from this point on we have to assume

you have found and repaired any malfunctions in the primary and secondary ignition system.

No Start

In order for an engine to start we must have compression, the correct ratio of fuel and air, and sparkdelivered at the correct time. Compression and ignition systems will not be covered here but spark

must be present. In some systems if you do not have spark you will not have fuel. When you firstcycle, sometimes called tapping, the ignition key you should hear the fuel pump start, a slight buzz

from the rear, and then shut off after two seconds. We now determine that the buzz is not present and

we have no fuel pressure reading on our fuel pressure gauge. What do you do?

First is to check for voltage at the fuel pump. Using a voltmeter or an automotive test light check for

12 volts at the fuel pump when the key is cycled. We normally use a test light with the alligator clip


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connected to the negative feed to the fuel pump and the tip of the probe touching the positive feed to

the pump. This way you know you have a good ground and hot feed if the light lights up. If the lightlights up and the pump does not run the fuel pump is defective If the light does not light up you need

to check the ground and the hot separately. Connecting the test light to a known good ground tryagain. If the light lights up repair the ground wire circuit. If it does not light up the problem is probably

the fuel pump relay or fuse.

Engine Does Not Start ColdSpark Present

1. Incorrect or no fuel pressure2. Defective cold start valve

3. Defective thermal time switch4. Defective electronic control unitor wiring

5. Defective temperature sensor6. Defective pressure sensor

Engine Will Not Start HotOtherwise No Problems

1. No rest pressure caused by defective fuel pump check valve

2. Leaking fuel injectors after shut off3. Defective fuel pressure accumulator

4. Defective cold start valveleaking5. Defective thermal time switch

6. Engine overheated

Engine Runs Rich

1. Defective fuel pressure regulatorcheck fuel pressure and adjust.2. Defective cold start injectorcold start valve is leaking

3. Defective injectorinjector stuck open or leaking4. Defective pressure sensor

5. Defective temperature sensor

6. Defective electronic control unit

Engine Runs Lean

1. Clogged or dirty fuel injectors

2. Low fuel pressurecheck and adjust

3. Defective electronic control unit4. Defective pressure sensor

Engine Misfires

1. Defective trigger contacts2. Defective injector or injectors

3. Defective series resistor


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4. Defective pressure sensor

5. Defective electronic control unit

Idle Too High

1. Vacuum leak2. Auxiliary valve not closing3. Incorrect base throttle plate setting

4. Air by pass screw not adjusted properly

Idle Too Low

1. Coldauxiliary air valve defective

2. Hot Incorrect base throttle plate setting3. Air by pass screw not adjusted properly

4. Improper fuel mixture caused by a rich or lean condition.

Idle Hunts

1. Vacuum leak2. Defective throttle switch

3. Improper fuel mixture caused by a rich or lean condition.4. Defective trigger contacts

5. Defective or clogged injectors6. Defective pressure sensor

Full Throttle Output Poor

1. Defective throttle switchfull load enrichment switch is bad

2. Defective pressure sensor3. Improper fuel pressure and or fuel pump volume

Engine Hesitates

1. Defective throttle switch

2. Defective pressure sensor3. Improper fuel mixture caused by a rich or lean condition.

4. Defective electronic control unit5. Defective fuel pressure regulatorsome regulators have a vacuum line, which increases fuel

pressure as intake manifold drops.

Some Quick Tips To Check The System

Electronic Control Unit


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The electronic control unit is normally very reliable. Before you change the control unit make sure you

have gone to a wiring diagram and checked all the 12-volt inputs and the necessary grounds at thecontrol unit wiring connector. Although it may seem like the control unit works on magic it does not.

Wiring is the most common cause of the control unit not working. The electronic control unit shouldonly be changed after you have checked every sensor and all the wiring. Most control units have an

adjusting screw on the top of the unit, which is a fine tune for the fuel mixture. You can smooth outyour idle by turning the screw in or out until the engine idles smoothly.

Cold Start Valve And Thermal Time Switch

The cold start valve is another part that does not fail often. Usually the reason it does not fire is due toa defective thermal time switch or the wire fell off the starter. You can unbolt the cold start valve from

the intake and place it in a glass beacon. Ground the coil wire and tap the ignition key. The cold startvalve should fire a very fine atomized spray if the temperature is low enough and should not leak when

you turn the key off. Check your manual for the correct procedure for your car. The temperature at

which it will activate is usually marked on the casing of the thermal time switch.

If the cold start valve does not fire check the starter solenoid wiring. If the wires are in place, check to

see if you have current flow in and out of the thermal time switch. If you have current flow in but noneout and the temperature of the coolant is below the specified rating of the thermal time switch that

thermal time switch is defective.

Tech Tipif the engine starts then stalls after a few seconds the cold start valve is probably good. That

is why the engine started. The engine started and ran on the amount of fuel the cold start valveinjected and then stalled because something else is askew. The cold start valve has no effect on the

performance of the engine during warm up. Check the other conditions above and below.

Trigger Contacts

The trigger contacts are housed in the lower section of the ignition distributor underneath the

mechanical centrifugal advance plates. On a V-8 engine the trigger contacts have a set of four points.The trigger contacts signal the "start" of injection while the "duration" of injection, which is how long

the injectors remain open, is determined by the inputs of the pressure sensor, engine speed, and thevarious other engine sensors to the electronic time switch of the ECU.


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If your engine is misfiring badly, barring an ignition problem, the most common culprit is the trigger

contacts. Since the points do not have current flowing through them, unlike ignition points, the pointcontact surfaces last for quite a long time and are not subject to the pitting that occurs on ignition

points. However, the rubbing blocks wear out, just as ignition points, because of lack of lubrication andfrom normal wear. This will result in the failure of the ECU to receive the signal to fire a pair of

injectors, thus the bad miss. Another problem is the point contact surface corrodes causing the same

scenario.

We have mentioned that you must check the connectors before replacing the parts; this is one area

that we have seen frequent connection problems. There are two different types of trigger contacts. Thepigtail type has a short wiring harness that is connected to the trigger contacts and the other type has

no wiring attached just the male ends. Make sure you check the pigtail connector for any reason thatcould cause a poor connection. It does not take much to cause a really bad misfire making it seem that

the engine is running on four cylinders. The truth is, it probably is.

You can tell that injectors are not receiving the signal to fire it by testing with a 12-volt test light.

Connect the alligator clip to ground, pull back the connector boot and so you can touch each wireconnector of the injector with the probe. When the engine is running one wire will have a solid light

and the other wire will flash or pulse. When this is occurring the injectors have the proper electricalsignal to fire.

If both wires have a steady light the injector is not receiving the ground from the control unit. Youneed a hot and a ground to pulse the injector. Two positives don't make a negative in this case. The

most common cause of the above scenario is the failure of the ECU to receive a signal from the triggerpoints either due to a wiring problem or a mechanical failure. Other causes may be a series resistor,

extremely rare, or a control unit failure.

Removing the two screws and sliding the trigger contact set out of the distributor will easily remove

the trigger contacts. Make sure you grease the rubbing blocks of the points when you reinstall them.

One final note on trigger contacts; although you can test the trigger points with an analog meter tosee if each set of points is working, we have found that there is a big difference with the results by

bench testing versus driving conditions. We have seen many contact sets check out good on thebench, when they are only subject to very slow RPM, but fail miserably under driving conditions. My

personal rule of thumb is that if the car is an everyday driver and the contact points are decades old, I

am changing them for reliability sake.

Throttle Switch

The throttle switch is held on by two screws and is easy to test and adjust. Check your wiring diagram

to see which wires are for the full throttle enrichment contacts and for the idle contacts. With the

engine off, key off, and connector removed, you can check continuity with an ohmmeter at the idlecontacts and full throttle contacts. If you do not have continuity either the switch is bad or out of


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adjustment. If you do not have a wiring diagram, the black cover normally unclips from the switch and

then you can see the full throttle and idle contacts. They are the ones the sweep the non-zigzag path.Follow the yellow brick road to the appropriate connectors.

Tech TipHere is an easy way to check the adjustment of your throttle switch. This test is done withthe engine off, key on, air cleaner off. Slowly, very slowly advance the throttle switch to full throttle.

As you are moving the throttle forward you will hear audible clicks. Count the clicks as you continue tomove the throttle forward. You should hear twenty clicks from start to end and no clicks when you

release the throttle.

If you do not hear twenty clicks, loosen the screws on the throttle switch and adjust it. Repeat the test

above. If you hear clicking when you release the throttle the throttle switch is defective.

Temperature Sensors

The temperature sensor in the air filter housing measures the temp of the incoming. The sensor is avery fine tune and has very little affect on the engines performance. The resistance of this sensor is

about 400 - 500 ohms at 50 degrees F. and is about 150 - 200 ohms at 100 degrees F.

The coolant temperature sensor has the most affect on drivability. If the sensor is defective the ECU

may "think" it is minus 40 out and inject lots of fuel and run super rich. If the sensor is out of range,outside specified ohm reading versus temperature, the engine will experience drivability problems

during warm-up and normal operating conditions due to improper injector duration caused by an

incorrect resistance reading. Check your service manual for the specifications but the resistance shouldbe approximately 2,000 - 3,000 ohms when the engine is cold and less than 1,000 ohms whenoperating temperature is reached. Remember, the hollow threaded sensors contain a semiconductor

material whose resistance decreases as the temperature increases.

Some engines have an intake air temperature sensor in the intake manifold. This is actually the same

exact sensor as the coolant temperature sensor and this sensor can also affect the performance of theengine but not nearly as much as the coolant temperature sensor.

Tech TipOn engines equipped with both an intake air temperature sensor and coolant temperaturesensor you can compare the resistance readings after the engine sits overnight. Since the air will be

the same temperature as the coolant, the resistance values will be the same. If they are not one of thesensors is kaput. Check your resistance to temperature chart. If the coolant temperature sensor is bad

you can swap it with the air intake sensor for the time being to improve drivability.

Pressure Sensor

The pressure sensor is usually located on the left inner fender well. This sensor can affect performancemore than any other sensor in the fuel injection system.


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The sensor has two coils and a diaphragm inside. The coils can be tested using an ohmmeter. Check

your service manual for the proper pins and readings but the general rule if thumb is, 90 ohmsresistance for one coil and 350 ohms resistance for the other.

If the metal diaphragm inside develops a leak, the engine may not run or will run super rich. Any easy

test is to blow into the sensor, yuck, and see if the diaphragm leaks.

When the pressure sensor fails it is more common to have a rich running engine although it is possible

to have a pressure sensor fail where the engine runs very lean. The pressure sensor is not supposed tobe adjusted but if you are the type that has to mess with it even when you are told not to, make sure

you set it using a gas analyzer and not by ear. Turning the screw, located behind the epoxy, in willlean the mixture and turning it out will richen the mixture. Our theory on this is that you should

replace the pressure sensor if it is out of specification instead of trying to put a band-aid on theproblem.

Fuel Injectors

The three common problems are leaking fuel internally into the engine, leaking fuel externally from the

hose or from the plastic itself, and poor spray pattern due to clogging.

If the injectors are leaking fuel between the plastic housings they cannot be repaired. If they are

leaking fuel into the engine after you shut the engine off we recommend that you replace them sincewe never have achieved good results by cleaning them.

If the rubber hoses are cracked and beginning to leak you can buy a repair kit to fix that problem. The

kit consists of instructions, fuel injection hose and fuel injection clamps. Follow the manufacturer of thekits instructions and be sure to install new seals.

Tech Tip. cleaning injectors. D Jetronic injectors are one of the few injectors where we have seen

dramatic performance increases after cleaning.

If you suspect your injectors may need cleaning , remove the injectors and place each injector in agraduated tube. The ignition system must be disabled to prevent sparks. Follow the instructions in

your service manual. Crank the ignition with the throttle depressed for 15 seconds for most engines.Measure the quantity of fuel in each tube. There should be no more than ten percent variation but I

am always looking for equal


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If the injector does not spray an atomized conical spray you can try to clean them. There are many

injector-cleaning systems that work well for injection systems that utilize a fuel rail. If you do not haveone of these systems, I have witnessed people removing the injectors and installing each injector to a

pump sprayer filled with injector cleaner. You can pulse the injector by making a wiring harness up toconnect to the injector terminals. After you connect one wire to each injector terminal, connect one

wire to the negative side of a AA battery and begin to pulse the injector by touching the other wire to

the positive tip of the AA battery. Repeat the process until the injector fire a fine atomized spray. Bevery careful when working with flammables, no sparks near the flammable. It stands to reason that if

you cannot obtain a fine atomized spray the injector needs to be replaced.

Auxiliary Air Valve

These are very easy to test. When the engine is cold, remove the hoses from the auxiliary air

regulator. Peer inside the valve and observe that the part of the opening is uncovered. Use a mirror ifyou need to. The colder the temperature of the valve, the larger the uncovered opening will be. If the

valve is not open it should be replaced.

Install the hoses back on and start the engine. Allow the engine to reach normal operatingtemperature and shut off the engine. Remove the hoses and peer in the valve. There should be nouncovered opening when the engine is hot.

Tech Tipif you see a small-uncovered opening in the valve try tapping on the valve very lightly andsee if it shuts. Some valves also rely on engine vibration to assist in closing.

Hot Start Woes

We just touched upon the hot start subject above, but since it is such a common problem, it warrants

further elaboration.

We all know that water under pressure will boil at a higher temperature than water that is not under

pressure. Well the same goes for gasoline. If the gasoline is not under pressure when you shut off yourhot engine, the fuel will boil causing the injectors to shoot blanks when you try to start it. This is

commonly referred to as vapor lock and the pressure maintained in the fuel rail is called rest pressure.

Remember when we tested our fuel pressure way up at the top of this article we mentioned rest

pressure. In order to maintain rest pressure you must have fuel injectors, cold start injector, fuelpump check valve, and fuel pressure regulator that do not leak down.

As fuel flows from the high-pressure side of the pump, on the way to the fuel rail on the engine, it passes

through a fuel pump check valve located at the outlet of the pump and the fuel pressure accumulator. The

purpose of these parts is to prevent fuel from flowing back to the tank after shut off which would result inloss of rest pressure.

The fuel pump check valve is basically a small steel ball pushed against a seat by a spring. When fuel

pressure overcomes spring pressure and the fuel flows forward under pressure to the fuel rail. Whenthe pump shuts off the ball is firmly seated against the seat so fuel cannot return to the tank.

The fuel accumulator's job is to push approximately 6 ccs of fuel forward after shut off. This will

momentarily show a slight increase in the fuel pressure, and then the pressure will bleed off to


18/18

approximately 24lbs., check your specification, then finally fall to final rest pressure, say 18 lbs. after a

few minutes. When the pressure falls to the final rest pressure the accumulator's job is done. Thesystems maintains this pressure because the fuel pump check valve will not allow the fuel to return to

the tank on this side of the fuel rail.

Now we have incoming side of the fuel rail sealed up, we will discuss the fuel return side of the fuel

system. As fuel is pumped into the fuel rail at high pressure the spring pressure of the fuel pressureregulator is overcome and excess fuel returns to the tank unrestricted and constant pressure is

maintained in the fuel rail. Because of the fuel accumulator and the fuel pump check valve prevent thefuel from running backward when the engine shuts off we must now look at what seals the pressure on

the return side of the fuel rail.

When you turn off the engine you consequently turn off the fuel pump. The excess fuel pressure,

which the fuel pump delivers, is gone and the fuel pressure regulator closes since the fuel pump fuelpressure is lower than the fuel regulator's spring pressure. The closing of the fuel pressure regulator

seals the fuel from returning to the fuel tank via the fuel return hose. Now we have fuel underpressure trapped in the fuel rail. If the injectors and the cold start valve do not leak we have rest

pressure.

If the fuel pressure stills drops to zero after establishing the fuel pump regulator, the fuel accumulator,

and the fuel pump check valve are good, the problem now points to leaking injectors or cold startvalve.

Tech Tip. You can easily test, and narrow down, whether you have a condition that would cause youto lose rest pressure by using a pair of needle nose vise grips with rubber hoses installed over the

jaws. The hose on the jaws is to prevent damage to the fuel line.

Install a fuel pressure gauge in the fuel rail. Shut off the engine and see if rest pressure is lost. If so,

start the engine again and then shut the engine off. As the rest pressure is dropping pinch off beforethe inlet hose of the fuel rail with the vise grips. If the pressure ceases to drop you have either a bad

fuel accumulator or check valve or both. If it continues to drop after pinching the hose repeat the test

by pinching off the fuel return hose. If you pinch the return line off and the pressure stops droppingyou know you have a bad fuel pressure regulator. If the pressure still drops you have no narrowed itdown to the injectors or the cold start valve. Check each one at a time and replace as necessary.

After making the above repairs you will now be able to start your engine when it is hot. No more

sweating bullets when you go into the convenience store for the beverage of your choice.

Fuel Dampeners

One parting thought before we go. Some manufacturers installed pressure dampeners in the fuel line

before and in the fuel rail. These are simply little dashpots with an inlet and outlet. If these start toleak you can simply remove them and place in the circular file. You can't buy them anymore nor do

they serve much purpose other than to prevent a little noise.

We hope you have a better understanding of your D Jetronic system. Good luck and be sure you read

your manual for proper procedures pertaining to your car and follow every safety precaution whenworking with fuel.

BOSCH D JETRONIC Fuel Injection of Renault 17 TS

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