Too rich fuel from fuel injectors

My car is 1972 Mercedes Benz M116 3.5 V8 D-jetronic. I noticed my spark plug are burned to dark and floated with rich fuel, and my car is dead.
I have checked my ignition spark that is very good. And, the resistance of air temperature sensor coolant temperature sensor are of standard. The wiring has not short to ground.
Also, I have checked MAP sensor, when I put 0.5 bar pressure in it, it can hold over 1 minute to 0.45 bar.

I have no clue what to start with? Any comment will be greatly appreciated.

Thanks a lot.

Hi, Danny
did you check the resistance of the sensors directly or at the ECU?
Maybe there is no contact, this would enrich the mixture extremely.

The behavior of your MAP sensor reads good.

What about the trigger contacts? Might be when they are totally worn they flutter and produce extra pulses.

What about the fuel pressure? Does the system hold the pressure or does it get lost quickly? Injectors could be leaking.

Did you check the function of the cold start valve? Misfunction could be it stays open on normal engine run or is leaking.

That's all for the moment.

Regards
Norbert

Thank you for you prompt reply.

I will go ahead the testing you suggested and post it here as soon as possible.

Thank you again.

Hi, I am back with few latest update.

First, the direct resistance of engine temperature sensor when the engine temperature is 20°C is 2.78KΩ. And, the resistance of engine temperature sensor at ECU when the engine temperature is 20°C is 2.77KΩ.

Second, he direct resistance of air temperature sensor is 0.25KΩ, and the resistance of air temperature sensor at ECU is 0.28KΩ

Third, this morning I have check the fuel pressure as you suggested. I turn on and off the ignition serveral times to make the fuel pump start working until it build up 2.1bar. Then I turn off the ignition and watch the gauge for 30mins, the fuel pressure did not drop to or less than 1.9 bar. That means it can maintain the 1.9 bar fuel pressure throughout the rail.

Forth, I start cranking the engine, and the engine is capabale for running for 5mins before the car died. Then, I try cranking the second time, the engine did not run this time. Therefore, I dismantle all 8 injectors and the rail, and place the 8 injectors into the containers for checking. When I start the ignition, only 4 injectors with cylinder No. 2,4,7,8 sprayed the fuel, no fuel from other injectors, and the fuel pressure guage showed a significant drop from 1.9bar. Then, I further cranking the engine, the 4 injectors with cylinder No. 2,4,7,8 sprayed even more fuel out of it, still no fuel from other injectors.

Fifth, I think the trigger may be the problem for not sending signal to the other 4 injectors with cylinder No. 1,3,5,6. So, I dismantled the trigger and rotated it . I noticed that each 4 contact point of the trigger, only open and close for one time every 360° turnaround. Is it normal or a problem?

Thank you again for your time and feedback.

Hi, Danny
it is correct the trigger points open only once on any distributor-revolution. But all four close / open at different times, the distributor-camshaft is divided into two different cams.

I must tell you it's time to test the ECU. I don't know where you are situated and what is the best way get another ECU for testing or a repair..

Don't give the ECU to a service that can't handle this special device.
This is an analog device - not a digital one. 'Modern' technicians can't handle this any more.
Replacing parts will result in having to replace other components, the unit has to be re-adjusted for retaining a real proper function.
Please read the information provided here: jetronic.org/en/d-jetronic/ecu#Reparatur

Regards
Norbert

Thanks for your comment.
I have read the information you provided. That is very useful. As the article suggested, two third of all ECU he tested are correctly working. I am quite support this statement. But, in case of ECU failure occurred, can you teach me the basic troubleshooting for the ECU?

Also, I noticed that the adapter of coolant temperature sensor is broken, and there is one brown wire and one white-blue wire out of it. Are they interchangeable?

For my curiosity,if the trigger points open only once for all 4 contact points, there should be only 4 signal sending to the ECU. How is the 4 signals going to give 8 fuel injection for 8 cylinders in a correct time intervals? It does not seems matched.

Thank you again for your time and responses.

Hi,

sorry to jump in now as I was on vacation

It is correct that each trigger contact opens only once per ignition distributor rotation or every 2nd engine rotation. So you should check that each trigger contact is correctly seen by the ECU. Either via oscilloscope or via multimeter measuring average voltage in operaton.

If that works well, check contact 3,4,5,6 output to injectors. If all show the same average voltage, then it is the ECU.

dnadanny1 schrieb: Thanks for your comment.
...
Also, I noticed that the adapter of coolant temperature sensor is broken, and there is one brown wire and one white-blue wire out of it. Are they interchangeable?

For my curiosity,if the trigger points open only once for all 4 contact points, there should be only 4 signal sending to the ECU. How is the 4 signals going to give 8 fuel injection for 8 cylinders in a correct time intervals? It does not seems matched.
...

Hi,
the wires of the temperature sensors are interchangeable.

It is correct you have only 4 injection signals. The injectors are paired - two 'fire' at the same time. At Jaguar V12 even 6(!) injectors fire at the same time.

Regards
Norbert

Thank you for your information.
BTW, the wires in the injectors can also be interchangeable?

Yes the injector cables can be changed, no problem.

Thank you for your help.
I had checked ECU and electronic injector plugs as you suggested. The result is that:
1) 24 pin and 16 pin in the ECU have above 11.5 volt which is normal.
2) I had checked all 23 pins adapter wires in ECU (2, 25 are empty). And there is no break and no ground.
3) I had unplug all electronic injectors plugs from injectors, and tested its voltage. When I cranked the engine,
1 cylinder (4 volt)
2 cylinder (9 volt)
3 cylinder (4 volt)
4 cylinder (9 volt)
5 cylinder (4 volt)
6 cylinder (4 volt)
7 cylinder (9 volt)
8 cylinder (9 volt)
it is weird that as far as I know, the voltage to injectors should be under 3 volt. I have no idea why this happened.
Thank you again.

Hi Danny,

dont worry, what you measure is haevily dependent on your measuring equipments integration function. An oscillosope would show better results.

So I understand you measure on the connectors of injectors. Can you also please measure pins 21, 22, 13 and 14 for the incoming signals from trigger contacts. With ECU connected and while cranking. Afterwards we should know whether the fault is on T.C. or on ECU.

Thank you Volker.
I had tested as you suggested. I measure the voltage in ECU using multi-meter, when they are all connected.

When cranking, the trigger contact output to ECU are as follows,
1) pin 13 against pin 12 = 1~3volts
2) pin 14 against pin 12 = 1~3volts
3) pin 21 against pin 12 = 1~3volts
4) pin 22 against pin 12 = 1~3volts

When cranking, the ECU output to injectors
1) pin 3 against pin 11 = 0.1volt
2) pin 4 against pin 11 = 0.1volt
3) pin 5 against pin 11 = 0.1volt
4) pin 6 against pin 11 = 0.1volt

I had plug some LED test light bub specialized for testing the signal from ECU to injectors into the injectors adapters. Yesterday, 2,4,7,8 cylinder light bub is on and with very strong light. But, today, none of the light bub is on.

What should I do next? Volker.

Thank you very much.

Hi Danny,

sorry I somehow misunderstood that you have a Mercedes-Benz 350. Now I read in parallel thread that it is a BMW. Which one is true? If it is a BMW you only have 2 trippger contacts on pins 21 and 22 .

However, 0,1 V on pins 3 to 6 is wrong. And it seems to be a new error as you had only partial failure before.

Sorry Volker.
I have 2 car (BMW and Mercedes Benz). This thread is open for my Mercedes Benz
Another thread you saw is about leakage on my BMW.

Volker schrieb:
However, 0,1 V on pins 3 to 6 is wrong. And it seems to be a new error as you had only partial failure before.

I am confused and have no clue that it had started before, and it does not work intermittently. These days, it seems it is getting worser.

BTW, I am using multi meter for testing now. You suggested me to have an oscilloscope for better result. Can you recommend one oscilloscope for me?

Hi Danny,

I use RIgol DS1074Z. You need an analogue 4 channel oscilloscope. Bandwidth is not that important.

Thank you. I am looking it on my country's stores right now.

HI, Volker. I tried the Spray test as you suggested on the Chapter 5: Injection valve. I noticed when I turn my key to ignition position (not cranking or start the engine), some of the injectors have sprayed fuel. Is it normal?

Thank you

Hi Danny,

no injectors shall only open when cranking or when pushing down gas pedal. Looks like they need an ASNU treatment I do not know whether that is available in HK. If not, send to asnu.de (Prickartz Consult).