M103 engine doesn't start
 

Hi

Yesterday, I drove about 3 miles and went shopping (no problems so far). When I returned, the engine didn't start. The starter turned. I then tried with half and full gas. Now, sometimes the engine stumbled for a few seconds below 500 revs. A few times the engine even fired correctly up to 700 revs, but only for 1-2 ignitions. Finally, after 30 min the engine coughed up to 1500 revs and then roared as it should.

I returned home. The idle was more or less stable but it would have stalled when starting up hill. Otherwise the car was running fine. At home I tried to restart the engine after another 30min: negative.

Does anyone have a test procedure? The fuel pump was buzzing and I smelled some fuel after starting for a while.

Cheers
Tom

Do a search on OVP on this site - sounds like yours may be on it's way out.

I already fixed a broken solder joint at the OVP some months ago. Besides, my ABS light is off (has also been off with the broken joint ;-) ). With a half broken joint (as I had last time) I would also assume to have a rougher idle.

Any other idea?

If you are most certain it is getting gasoline...

How about the coil?

Or a burnt ignition distributor cap/rotor...

What about jumped timing? Is it possible for the timing chain to have jumped a tooth?

Clogged catalytic converter?

Finaly a faulty fuel pump relay?

I assume it has to do with the cold start control. Today I tried to start the car at different temps.

It worked at 30°C (todays temp), a bit above 40, >90

It did not work at a bit above 80 and around 60°C.

Since the idle rev at a bit above 80 is at the warm idle ref, I assume it is not the temp sensor.


The ignition distributor is 1 yr old, the ignition cable and the fuel filter 6 months

Sounds like a coolant temp sensor problem. Check the resistance at different temperature.
Good luck,
Meza

No, it's not the temp sensor. I meanwhile checked the following

Start and kill the engine every 2 minutes until temp >80°C. No problems.

Drive a bit, park car, kill engine, restart: no problem

Restart after 15 min: doesn't start.

Replace temp sensor with 320 Ohm resistor (=80°C): doesn't start.

Wait a while until car starts, drive a bit, kill engine, switch on ignition every 15s to keep system fuel pressure up (fuel pump starts with ignition on for 2s) for 20min: doesn't start


Now, I have no idea left what to look for. It seems as if it would be a timing problem after the car ran for a while.

I thought to have solved the problem but it reoccured.

After my last thread, I bridged the pump relay to keep pressure up what didn't help. So finally I opened the ignition distributor and the 1 yr old Beru cap was crap. I cleaned it and drove for 1-2 weeks without further problems. Then I installed a new Bosch cap and only a few days later I had problems. Ok, so far I kept the 1 yr old rotor inside, since it still looked fine.

However, when I tried to start the car, I didn't smell fuel, although I pushed the throttle. And this time the car stalled during idle with the engine running (after a 2 miles drive). Before, I "only" couldn't restart the car between 10 and 90 minutes after switching it off but it never stalled in the first place. With ignition on, I heart the fuel pump running for 1-2 s and simultaneously I felt a vibration at the fuel distributor, as if the fuel pressure was built up. And again, after 90 minutes with the engine cooled down, I could start the car and was able to continue my trip without further trouble.

Since I don't have so much time currently and need the car for my vacation in 2 weeks, could anyone (STEVE?) give me test procedure?!

Thanks
Tom

maybe some ideas?
 

Well, ignition modules can be receptive to temperature. Everybody kept telling me they never die on benz engines of that era, but sure enough mine managed to and it did some similar stuff before it finally fried (cutting fuel at odd rev points). Although it's not cheap (about $300 used) I managed to find one at a local yard for $15. The first thing I would do, however, is set up a dummy spark plug on one of your wires and watch it while somebody cranks the engine, if it's regularly firing while you're have starting problems then you can at least set your sights on the fuel system/fuel distributor. If it's not firing, then you know your problem is ignition based and you can look toward the coil, crank sensor, cap/rotor, EZL mdule, and the relays that supply power to these parts. Checking the igniton system's spark could mean the difference between changing a cheap relay and putting out $$$ for a fuel distributor you don't even need.