1971 Mercedes 250 CE with D Jetronic.

Hi everyone, my name is Steve, i am helping a friend restore a 1971 Merc 250 CE. We have rebuilt the engine and are now trying to get the D Jetronic to work.
We have checked continuity from the ECU to all components and all good. We have no power to the injectors, trigger points are ok and returning around 5V to ECU.
We have 12v to ECU pin 16 and 12v to pin 24 injectors. Suspected fault in ECU. We have purchased a used unit that we were assured was ok but same fault prevails. Can anyone give us a direction to go or could the replacement ECU be faulty also. Any help appreciated, Steve.

Hi Steve,
Welcome to the forum!

We need more information.
Does the fuel pump work? Do you have fuel pressure? Did you check the injectors?

I don't think you have two faulty ECUs, but you have to do some more testing.
It is not sufficient to check the wiring without the components installed.
In some cases the ECU won't work if electrical connections to components are missing or the components are faulty..
And - I think, you didn't check correctly. The trigger points don't 'return a voltage to the ECU' but 'shortcut' the lines to ground.
It makes no sense reading a voltage there.

Here is a link for instructions and a plan you can test the wiring harness and most of the components with:   jetronic.org/de/forum/jetronic/19-messpl...ents-by-car-model#68

Read the instructions and do all the checks and measurements. Then we can go further on.

Regards
Norbert
 

I will go through all the checks at the weekend. When you say remove poled 25 and test I don't see any checks involving pin 25?

Hi Steve,
the harness isn't connected to Pin 25.
This is the diagnosis-contact of the ECU, have a look at 3.7: jetronic.org/en/d-jetronic/ecu

Regards
Norbert

Ok, thanks. Is the wire just tucked away. Can this only be measured with an oscilloscope?

Yes, Steve - you need an oscilloscope to see the signal.

Regards
Norbert

Hi Thanks for all this fabulous info. All rests within spec apart from pins 9 and 20. Only have 9 reactions instead of 10. Removed throttle switch and cleaned it with electrical spray. Still only 9 but engine now running. Will this make much difference,S.

Hi Steve,
the TPS has to send this signals while you are opening the throttle to enrich the mixture in acceleration. 
One will not notice in real operation the signals near the end-position of the throttle are missing.
You will have the first version of the TPS installed in the car.
I think, the signals are missing because you had to adjust the switch in a position outside of the normal range because the contact-feelers for the idle-signals have bent <weakened> during the years.



You can see this switch had been adjusted to the end position... and in this position the last signals are missing.
Re-bend the marked idle-contact to the original position and you will have the 10 contacts re-activated after re-adjusting the position of the switch.

It's always a good idea to clean the TPS - but it's no good idea to grease it inside, even contact-spray can isolate, because there is extremely low electrical current there. Clean it - but don't grease the feelers or the board.

Regards
Norbert



 
 

Thanks again, Steve.