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.