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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026  | Fuel Injection Troubleshooting Troubleshooting D Jetronic No start and fuel pump not working; 1)Test the fuse,relay,wiring and fuel pump. No start and fuel pump working; 1)Test the main relay and power from ECU.Ensure there is a good ground from ECU terminal #11 to ground. 2)If the ignition system has a good spark,good power supply,ground to the ECU and continuity at the trigger points(cover this later) and injectors fail to pulse, replace the ECU. Starts when cold and dies when the key is released; 1)Trigger points in distributor lack continuity.When the engine starts,it is starting off of the cold start injector and as you release the key,the cold start injector shuts off. Stalls when engine is cold; 1)Inspect the auxillary air valve.When the engine is cold,remove the hose on the intake side of auxillary air valve and let air to be drawn into it.If the engine speed increases greatly,replace the auxillary air valve. 2)Temperature sensor 2 is also critical to cold operation. Misfire or unstable idle; 1)Ensure that the ignition system is in good shape and also the intake is in good order.These need to be confirmed first as they are more likely to cause this problem. 2)Inspect the circuits and sensors of temperature sensor 1 and 2 and continuity through both sides of trigger points. 3)Inspect the vacumm hose that goes between the pressure sensor and the intake manifold.It should have no kinks and not collapse with vacumm present. 4)If all the above check out,do an injector flow test. Misfire while driving; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Do a fuel pressure and volume test. 3)If the fuel pressure is constant,test temperature sensor 2,pressure sensor and throttle switch circuits. Power is suffering; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Most likely this is due to low fuel pressure.Do a fuel pressure-volume test and pay close attention for loss of pressure. 3)If correct,test the circuits of the pressure sensor and temperature sensor 2.If these meet specs,do an injector flow test. 4)If everything checks out,repeat this test. Stalls when you decelerate; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Inspect the hoses and wiring for good contact. 3)Check your throttle stop adjustment and curb idle RPM's. Smokes and runs rough; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Do a fuel pressure and volume test. 3)Inspect the circuits of the temperature sensor 2,trigger points,pressure sensor and injectors.If they check out fine,do a injector flow test. Misfire under Load; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Do a fuel pressure-volume test. 3)Inspect the circuits of temperature sensor 2, pressure sensor,trigger points and injectors. 4)If the above are good,do an injector flow test. Trailer hitching; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Do a fuel pressure-volume test. 3)Inspect the circuits of temperature sensor 2, pressure sensor,trigger points and injectors. 4)If the above are good,do an injector flow test. 5)Check the throttle switch. Idle speed too high; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Check and adjust the throttle stop and curb idle speed. Idle speed too low; 1)Ensure that the ignition system is in good shape and also the intake is in good order. 2)Check and adjust the throttle stop and curb idle speed. | ||
| #47940 |
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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026 | Re: Fuel Injection Troubleshooting Testing the D Jetronic Components Main relay; 1)There should be 12 volts at pin # 24 of the ECU. 2)If not,check for 12 volts at pin # 24 of the relay. 3)If 12 volts is not present at the relay but it clicks,replace with a new relay. 4)If there is 12 volts at pin # 24 of the relay,repair # 24 wire between relay and ECU. 5)If the relay does not click,inspect the wire from the main relay pin # 45 to ground. 6)If the ground is good and 12 volts at relay pin # 38 when the engine is cranked,replace the main relay. Trigger points; 1)With the engine not running and ECU harness disconnected from the ECU,check the resistance between ECU harness 12 and 21,then from 12 to 22.One should show a low resistance and the other should show an open circuit. 2)Rotate the engine 360 degrees and check the resistance.They should have an opposite reading now. 3)If not,perform the same test at the trigger points themselves.This will tell you if it a component or wiring fault. Temperature sensor 1 1)With the engine not running and the ECU harness disconnected from the ECU,connect an ohmmeter between ECU harness pin # 1 and 13.At an ambient temperature the reading should be 200 ohms. 2)If the resistance is well above 200 ohms,check resistance at the sensor itself to determine if it is a component or wiring fault. 3)Check resistance of all the terminals to chassis ground.There should always be an open circuit. Temperature sensor 2 1)With the engine not running and the ECU harness disconnected from the ECU,check the resistance between harness terminal 23 and ground.The resistance should be 2000 ohms at ambient temperature. 2)If the engine is near operating temperature,the resistance should be below 1000 ohms. Throttle switch 1)Test the throttle switch with the key on,engine off. 2)Slowly open the throttle,and as it opens the injectors should alternately click.You should hear 20 evenly spaced clicks. 3)If this is not met,place a 0.016 in.(0.4mm)feeler gauge between the throttle stop and throttle stop screw.Connect a voltmeter to terminal 17 of the throttle switch.The voltmeter should show voltage while the ignition key is in the on position.Remove the feeler gauge and the voltmeter should show no voltage now. 4)If this fails,loosen the screws and rotate the switch until it meets these requirements. 5)If they can not be met and voltage is always present no matter where you position,replace the throttle switch. 6)If the voltmeter reads no voltage,ensure voltage is being supplied to the switch.If so,replace the throttle switch. 7)If no clicks are heard while performing test 1 and 2,check wire numbers 20,17,14 and 9 for continuity end for end from the ECU to throttle switch. Pressure sensor 1)With the engine not running and the ECU harness disconnected from ECU,check the resistance from ECU harness terminal # 7 to 15.Should be 90 ohms and then check the resistance between # 8 and 10.Should be 350 ohms.If this is not met,test the sensor itself. 2)on occasion,the sensor resistance will check out,but will not hold vacumm.Using a hand held vacumm pump perform this test again (step #1) Injector circuit 1)With the engine not running and the ECU harness disconnected from ECU,check resistance of ECU harness pins # 3,4,5,and 6.All should have less than 25 ohms. 2)If the resistance is greatly higher or lower than 25 ohms,test the injector itself. 3)If the injectors pass,repair the wiring harness. | ||
| #47941 - in reply to #47940 |
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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026 | Re: Fuel Injection Troubleshooting D Jetronic Components Function -------------------------------------------------------------------------------- Sensors Trigger Points The trigger points are located in the base of the distributor below the ignition point breaker plate.These points are used to produce the signal that synchronizes the injector to the crankshaft.They consist of two low voltage,low current contact points which are driven by a cam located on the distributor shaft.Each set of points initiates the opening of one or two groups of injectors. Unlike ignition points,the trigger points can last 100,000 miles or more.As the distributor rotates,a pulse is created by the opening and closing of the trigger points.This pulse is sent to the ECU.The ECU uses this signal to open the injectors and will use the inputs from the other sensors to determine when to close them. Temperature Sensor I Temperature Sensor I is an ambient air temperature sensor.As the ambient air temperature decreases,the density of the air increases.As a result,the ECU must inject more fuel on a cold day than on a warm day. Temperature Sensor I is a temperature sensitive resistor known as negative temperature coefficient thermistor (NTC). This sensor has a resistance of between 400 and 500 ohms at 50 degrees F. At 100 degrees F.,the resistance is between 150 to 200 ohms. Temperature Sensor I actually has little effect on the operation on most D Jetronic equipped vehicles.This is because most of these cars have tens of thousands of miles on the engine and are running very rich due to this wear.The troubleshooting consequence of this is that disconnecting the air temperature sensor during the diagnostic procedure may have little effect on the way the engine runs,and in some cases it may actually improve the way it runs. Temperature Sensor II Temperature Sensor II is the coolant temperature sensor on water cooled engines.Like temperature sensor I, it is a NTC thermistor.The temperature of the engine is important because the intake manifold design of fuel injected engine does not permit the use of an air restictive choke.Additionally,restricting the air to enrich the engine during warm up would cause inaccurate readings from the manifold pressure sensor.The warm up choke function is therefore performed by Temperature Sensor II. When the coolant temperature is about 50 degrees F.,the resistance of Temperature Sensor II is between 3000 and 4500 ohms.As the temperature increases to more that 120 degrees F.,the resistance drops to less than 1000 ohms.Thus the sensors work is done once the engine is warmed up.Also it must be continuously remind the ECU that the engine has warmed up.If damaged,Temperature Sensor II will not continue to partially function( such as the resistance values shifting). It will completely fail,creating an open short or ground. An open circuit in Temperature Sensor II or the wiring leading to it will cause the engine to run extremely rich once warmed up.Symptoms would be dark smoke from the tailpipe (most noticable at idle),rough idle and poor power.Keep in mind that these same symptoms could also be caused by engine compression problems and ignition. Should the sensor become shorted or the wiring harness grounded,the effects may not be noticable at all when the engine is warmed up.The symptoms would be more like a carburetor with the choke stuck open-rough or erratic idle,stalling or hesitation when the engine is cold and progressively running better as the engine warms up. Throttle Switch The throttle switch tells the ECU when the throttle is closed,when the throttle is wide open and when the throttle is moving toward the open position.The switch consist of twenty two contacts,with a set of wiping contacts that move across them as the throttle progresses from the closed position to the wide open position. One wiping contact is used to inform the ECU that the throttle is closed.Another makes contact only when the throttle is wide open and a third makes and breaks contact twenty times as the throttle opens.The electrical pulses created by the making and breaking of the contacts signals the ECU to open the injectors more frequently,thereby enriching the mixture for acceleration.This feature behaves much like an accelerator pump on a carburetor. Symptoms associated with a defective throttle switch include a rich(smoky)idle and hesitation.An intermittent condition at cruise-which feels like you shut off the engine and immediately turned the key back on,can also be caused by the throttle switch. To test the throttle switch,open the throttle with the key on but the engine not running.The injectors should open exactly twenty times,evidenced by twenty evenly spaced clicks. Pressure Sensor The D Jetronic pressure sensor is known as a linear variable displacement transducer (LVDT).It consist of a pair of coils,one with about 150 ohms of resistance and the other with about 85 ohms of resistance.An iron core attached to a diaphragm runs through the center of these coils.As changes in manifold pressure moves the diaphragm,the iron core moves inside the coils,causing ripples in the current flowing through these coils.This signal is used by the ECU to monitor the relationship between barometric pressure and manifold pressure. The most common symptom from a defective pressure sensor is a rich running condition.Of course rich running can be caused by several other defects as well. Of all the sensors used on D Jetronic,this one both the easiest and the most difficult to test.Usually a simple resistance test of the coils is enough to determine if the unit is good or bad.On the other hand,the only way to be sure is to replace it with a known good unit. Electronic Control Unit (ECU) The ECU receives input signals from the pressure sensor,Temp Sensor I,Temp Sensor II and the throttle switch to determine how long to leave the injectors open.It is only able to respond to air-fuel ratio request from one sensor ata time.As a result,whenever a sensor fails,the tendency will be for the ECU to send the injectors a full rich supply of fuel. The electronic unit has no servicable components.In the event of a failure,the ECU is replaced as a unit.Failures are extremely rare and usually result in a no start. D Jetronic that have an adjustable air fuel ratio have a detent potentiometer on the side of the ECU.This potentiometer can be used to fine tune the air-fuel ratio during a tune up. Pin # 19 and 25 of the ECU are connected to the fuel pump relay.When the ignition switch is turned to the on position,the ECU energizes the fuel pump to ensure that the fuel system is filled for ease of starting.If the engine is not cranked,the ECU will shut off the fuel pump after one or two seconds.If the engine is started,the fuel pump runs continuously until the engine is shut off. | ||
| #47942 - in reply to #47940 |
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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026 | Re: Fuel Injection Troubleshooting D Jetronic Fuel Components In Tank Filter Located inside the fuel tank is a screen or filter designed to protect the fuel pump from rust,dirt and debris.Although seldom the cause of a drivability problem,the in tank filter should be high on the list of items to check.In many cases these filters have been ignored,even on well maintained vehicles. Fuel Pump The fuel pump is a high speed roller vane pump.It is capable of pumping fuel at pressures and volumes much higher than the engine or injection system would ever require.This type of pump is very efficient at pushing fuel bur does not do a good job of pulling fuel.As a rsult,these pumps are located very close to the fuel tank or even inside the fuel tank to reduce the chance to vapor lock. The fuel pump can react adversely and even fail as a result of using some fuel additives.Use extreme when selecting them to ensure that they do not contain methanol or other corrosive substances. A defective fuel pump can cause low fuel pressure which would result in symptoms such as hesitation,stalling and poor power.Often a defective fuel pump bypasses the poor running stage and simply stops operating.This causes the engine to die or keeps the engine from starting. Fuel Filter The fuel filter is the only real protection the injection system has from internal contamination from dirty fuel.Therefore the filter should be changed every time the spark plugs are changed. Fuel Pressure Regulator The fuel pressure regulator used on D Jetronic systems consist of a valve connected to a spring loaded diaphragm.The regulator controls the fuel pressure at 28-32 psi and is adjustable so it can ensure the proper fuel pressure throughout the life of the vehicle.Incorrect fuel pressure can cause a lean running engine if the fuel pressure is too low and a rich running engine if the fuel pressure is too high. A defective fuel pressure regulator can result in high fuel consumption,rough or erratic idle and poor power. Injectors The injectors are solenoid operated,normally closed valves controlled by the ECU.Grounded to the engine block or chassis,each injector is opened by a 3 volt pulse from the ECU.The lenghth of the pulse is only a few milliseconds(2 to 5),and it takes time for the injector to close from the spring tension.Thus the injector is open for a total of about 3 to 6 milliseconds. Very little goes wrong with the D Jetronic injectors themselves.An occasional burned out solenoid winding or restriction from contamination is the most common problem.Another problem is leaking from the hoses that attach the injector to the fuel rail. Typical symptoms of injector problems include rough idle and poor power. Fuel Rail The injectors and the fuel pressure regulator are attached to steel tubing known as the fuel rail.The inbound fuel lines from the fuel pump and filter feeds fuel to the injectors and the fuel pressure regulator through the fuel rail. As a passive component of the system,very little can go wrong with it except for leaks and restrictions. Cold Start Injector Also attached to the fuel rail is a solenoid operated valve known as the cold start injector.Since the earliest applications of the D Jetronic system were four cylinders,the cold start valve picked up the moniker "fifth injector." It stuck in some circles,even for six and eight cylinder applications. The cold start injector receives battery voltage whenever the starter is engaged and is grounded through a device known as a thermo-time switch.The thermo-time switch is a temperature sensitive bimetal switch designed to provide a ground for the cold start injector when the temperature of the engine is less than 95 degrees F. A second circuit in the switch is an electric heating element intended to heat the bimetal as the engine is being cranked. Consequently,the cold start injector should operate only when the engine is being cranked,the temperature of the engine is less than 95 degrees F. and for a maximum of five to twelve seconds. Two of the most common symptoms of a cold start injector problem are hard starting when cold becuse the cold start valve is not operating and a leaking cold start injector which can cause an extremely rich running condition. | ||
| #47943 - in reply to #47940 |
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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026 | Re: Fuel Injection Troubleshooting Troubleshooting K Jetronic Engine turns but won't start 1)No fuel pressure; Test the fuel pump and pre-pump and do a fuel pressure and volume test. 2)Jammed and/or sticking airflow sensor; Remove the boot that goes to the intake and loosen the center line on fuel distributor.This will relieve the control pressure.Press down on the center bolt of the plate and you should feel no resistance or binding.Also check that the rest height and centering are correct. 3)Auxillary valve is sticking; 4)Defective cold start injector; If the injector does not function,the air-fuel ratio will be lean,preventing easy start up. 5)Shorted or defective thermo time switch; The cold start injector will not work if the thermo time switch is defective.Check this in the event that your cold start injector does not function before replacing. 6)Control plunger sticking; Remove the fuel distributor from the airflow sensor and check to see if it moves freely. 7)Restricted injectors; For this to be the cause,they would have to be severely restricted,which is why I listed it last.Do an injector flow test and ensure that the delivery is near equal. Hot starting difficulty 1)Loss of rest pressure; Do a pressure test and focus on the rest pressure.If it does not pass,check for a defective fuel pump check valve,defective fuel distributor,faulty system pressure regulator and leaking cold start injector. 2)Airflow sensor adjusted incorrectly; Check height,centering and for binding.Remove the boot and loosen the center line on fuel distributor to relieve control pressure. 3)Sticking or binding of the control plunger; Remove the fuel distributor and ensure that the control plunger moves freely. 4)Injectors leaking; Remove the injectors from the intake manifold and with the ignition key on/engine off,press on the center plate to pressurize the system.Inspect and replace any injector that is leaking. 5)Cold start injector leaking; Same test as above. 6)Shorted thermo time switch; Cold start injector is dependent of this component. 7)Incorrect control pressure; Do a pressure test and verify that the warm control pressure is within spec. Rough idle (cold) 1)Cold control pressure incorrect; The movement of the control plunger will be limited if the cold control pressure is too high.This in turn will limit the amount of fuel able to be delivered through the injectors.The result will be a lean ratio and will cause rough idle. 2)Auxillary air valve defective; If defective and not opening,idle cannot rise and results in rough idle. 3)Airflow sensor adjusted improperly or binding; If the movement is not smooth,it will result in air-fuel ratio errors. 4)Leaking cold start injector; If the cold start injector is leaking,the engine will be overfueled even if cold.If the cold start injector is leaking,the idle will get worse as the engine temperature increases. 5)Injectors have an unequal flow or spray pattern; Do an injector flow test and replace any that do not deliver the correct amount of fuel or have a poor spray pattern. Runs rough (warm) 1)Warm control pressure incorrect; Incorrect warm control pressure that is too high or low will cause an incorrect air-fuel ratio,thus resulting in a rough idle. 2)Airflow sensor adjusted improperly or binding; If the movement is not smooth,it will result in air-fuel ratio errors.Check for centering and correct rest height. 3)Leaking cold start valve; Again,will result in overfueling the engine,resulting in a rough idle. 4)Injectors have an unequal flow or spray pattern; Do an injector flow test and replace any that do not deliver the correct amount of fuel or have a poor spray pattern. Stalls after starting (warm) 1)Warm control pressure; If the warm control pressure is too high,the air-fuel ratio will be lean. 2)System pressure incorrect; If too high or low,the air-fuel ratio will be incorrect. Idle speed high 1)Check auxillary air valve; Ensure that it is closing. 2)Vacumm leaks; Self explainatory. 3)Check the minimum air; Self explainatory. Backfire in intake 1)Check that CO adjustment is correct; If incorrect,backfire will result if started and under a load. 2)Boot between airflow sensor and throttle defective; Will result in a lean mixture due to secondary air(false air) 3)Vacumm leaks; Self explainatory. Misfires 1)Ignition; Inspect the cap,rotors,wires and plugs. 2)Fuel delivery inadequate; Check for binding of airflow sensor,control plunger, incorrect control or system pressure and restricted injectors. 3)Injectors; Unequal delivery or poor spray pattern.Do a test and replace any that are defective. Poor power 1)Control pressure too high; If the control pressure is too high,the control plungers travel will be limited,resulting in a lean running engine. 2)Check ignition components; Verify that the spark plugs,wires,cap and rotor are not worn. 3)Injectors restricted; Do a test for delivery.If an injector is restricted,fuel delivery will be limited,thus power will suffer. Sag or stumble when accelerating 1)Airflow sensor plate binding or sticking; If binding or sticking,fuel flow will be limited. 2)Control plunger binding or sticking; If binding or sticking,fuel flow will be limited. 3)System pressure or warm control pressure incorrect; If too high,the travel of the plunger will be limited. 4)Injector flow unequal; Self explainatory. Diesels(run on after shut off) 1)Airflow sensor sticking or binding; The plate is not rising to position,continuing to deliver fuel. 2)Control plunger binding or sticking; Remove the fuel distributor and ensure that the control plunger moves freely. 3)Injectors leaking; Do an injector flow test and make sure that they seat correctly.Replace any that are defective. 4)Cold start injector leaking; Remove and pressurize the system and replace if it leaks. Fuel consumption high 1)Air-fuel ratio incorrect 2)Injectors leaking 3)Cold start injector leaking | ||
| #47944 - in reply to #47940 |
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| Nutz Expert Date registered: Apr 2006 Location: Vehicle(s): Posts: 2026 | Re: Fuel Injection Troubleshooting K Jetronic Specs Fuel pump relay Place an 8 amp fused jumper wire at fuel pump relay teminals # 30,51 and #87. Cold control pressure ( psi ) model_______50 degreeF. _75 degreeF._100degreeF._ 450 76-78 ----------19 24 34 450 79 ----------19 28 38 280 77(high-alt)---------17 25 33 280 (fed) ----------14 21 31 280 (Cali) ----------14 21 31 6.9 ----------16 25 34 System pressure ( psi ) 450 federal and california ---------- 75-84 450 1977 federal and high altitude---------- 75-84 280 1977 high altitude ---------- 75-84 280 california ---------- 75-84 280 federal ---------- 75-84 6.9 ---------- 75-84 Warm control pressure ( psi ) 450 federal and california ---------- 49-55 450 1977 federal and high altitude---------- 52-58 280 1977 high altitude ---------- 52-58 280 california ---------- 44-49 280 federal ---------- 49-55 6.9 ---------- 49-55 Rest pressure ( psi ) All ----------- 41 Return line (cc per 30 seconds) 450 federal and california -------------- 1100 450 1977 federal and high altitude-------------- 1100 280 1977 high altitude -------------- 930 280 california -------------- 930 280 federal -------------- 930 6.9 -------------- 1100 | ||
| #47945 - in reply to #47940 |
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