Trigger contacts Mercedes 280CE (W114)

First of all, thank you for a fantastic website and a forum with lots of great advice.

I have previously found help in solving various problems, but now I have a challenge with my lovely Mercedes 280Ce (w114) from 1974 (engine type M110) with D-Jetronic.

When it was parked for the winter, it was driving (allmost) perfect. There were only some periodic "hiccups" when driving at constant speed - as if the ignition og/fuel supply was interrupted in a split second. This could indicate a problem with the throttle potentiometer. However, it was very periodic, so I learned to live with it.

After the winter I started the car without problems, and drove a short ride. When I started the car after a few minutes again, it could not run properly at all. It started fine, with stalled as soon as I put the car in gear and tried to drive. .

My mechanic found that the temperature sensor on the motorbook was not working properly, so it was changed. It didn't help, though, so he looked at the throttle potentiometer, which had caused problems before. It's a bit worn, so I bought one from ebay which should be "neuwertig". When it arrived, it seemed like new, but it didn't work. When you turned on the throttle you could not hear the clicking sounds that you should be able to. He soldered the old potentiometer, which after that seemed to work, but the car would not run at all.

In fact, it got so much gas that the oil ran over because of gasoline in the oil. He therefore looked at the trigger contacts, which looked somewhat worn (see attached pictures).

I have contacted the Bosch service center, but it is not possible to get repair kits for the 6-cylinder versions (M110 engine), so we would like to know how to test the contacts. Can this be done without Norbert Fischer's smart tool?

The cams on the contacts looks a little worn, but it is difficult to measure them because of the plastic covering the contacts.

It has to be said that we simply changed the MAP sensor on suspicion, as I previously got hold of a MAP sensor (tested by Bosch Classic parts in Germany). It is the correct type for the car, but it made no difference. I have now got hold of a NOS throttle potentiometer, which I could receive in a few days. My mechanic, however, does not believe that the potentiometer alone can cause the problems.

I really appreciate any advice on how to test the contacts (and possibly repair them). It anyone has a set that they will sell to me, please let me know

Thanks in advance from Denmark

pjj5171

Hi unknown, I guess your parents did not name you pjj5171 ?

we like to feel like a big family where we call each otherby first name.

Worn trigger contacts can make injectors stop working but not a too rich mixture. Too rich a mixture comes from wrong fuel pressure, disconneted or broken temperature sensors (esp. engine temp), MAP sensor, vacuum leakage or in seldom cases ECU. It is important to measure sensors on disconnected ECU connector so that you see wiring harness issues. And on MAP sensor you should also measure isolation to ground.

Having said that your trigger contacts do not look well. As far as I know I am the only one who has developed a repair method for 4-6 cyl. small trigger contacts. Trouble is that you cannot swap cams as easy as on 8-cly T.C. . But if your symptoms is really a very fat mixture that does not come from them.

Hi unknown,
as Volker wrote before: You have to measure resistances etc. at the plug towards the ECU.
Problems at the wiring harness are not detected when you test directly at the components.

The throttle 'thing' isn't a potentiometer - it's just a switch. One should read only zero or very high resistance.
It has to be clean - not greased or oiled because electrical current is very low and oil or grease prevent from giving contact.

But the throttle position switch won't be the reason for your problems.
And - as Volker wrote - the trigger unit doesn't look good <some corrosion of one lead, too>,
but will not be the reason for the engine running rich.

Yes, you can adjust it using my tool, repair it or install a new one. I have some spares. You could contact me by PM.

Another reason for the engine running rich could be the cold start valve. It could be leaking -
try to disconnect the fuel line and install a dummy-bolt instead.

But check the resistances etc. first. You could use this plan: DOWNLOAD M110

Regards
Norbert

Hello Volker

I apologize if I acted rude. In many of the forums that I otherwise visit, you usually use your username. My name is Per Jorgensen.

Thank you very much for quick and thorough response. We will make the measurements that you and Norbert have proposed. I'll report back with the result.

Many greetings from Denmark

Per

Hello Norbert

Thank you very much for your good advice and the table of measuring points.

I am also concerned about the condition of the trigger contacts and have now spent a small fortune and very long time to get the car to run properly, so I am very interested in buying one of your trigger contacts since I have had no luck in sourcing them anywhere.

Kind regards

Per

I just wanted to follow up on this thread.

I replaced the triggercontacts (the old ones were very worn), but the car still didn't run porperly. There were new symptoms, that indicated a malfunctioning ECU. After replecement of the ECU, the car now runs perfect.

Cheers from Denmark

Per