Another stalling m103. What could it possibly be?
 

Have read a lot of threads on similar issues.
Today my 1987 300E stalled several times. The following happens:
One small hick up (in lack of a better word, not native English) then another one 10 sec later. Then the rev counter goes bananas, up to 2000 then down to zero a few times and then the engine cuts. It will start again immediately as normal, but cuts at once.

This has happened a few times for the past 6 months but today it was worse and happened many times and I found out the following: letting the engine cool down it started and ran as normal until it reached normal temp between 80 and 90 (C). As soon as it was warm it stopped again with the above symptoms.

I have just replaced OVP and fuel pump relay. Distributor cap and rotor has run around 25000 km and does not look too bad.

I am pretty sure it has to do with ignition rather than fuel. Or maybe some electronic cutting the fuel.

So, probably the CPS, right? As I understand there's is one sensor in front, and this is probably the one giving signal to rev counter and ignition module? But then there is another one in the rear of the engine and I'm not sure what this one does.

Anyway, I will order distributor cap, rotor, spark plugs, plug cables, and maybe both of these sensors tomorrow. Genuine parts - will cost a small fortune but then at least I can rule those out if the problem returns... Could it be something else? Occurring when the engine is warm only, cutting the engine as if turning the ignition key. Coil? Something else?

Hints, tips and general support is appreciated :)

cps is in rear..... sounds like a cps issue... although when i had it... i never had the engine rev up... it just got progressively worse as it warmed up.

You can test the crank sensor. It is the important one. Memory is fleeting me a bit but it should ohm out somewhere between 700-1200 ohms. The front sensor does nothing except provide info when the MB tech hooks it up to a special machine.

Sounds to me like you need an ignition tune up.


Please let us know how it turns out

Thanks! To clarify: The engine didn't really rev up. Just the rev counter had its own life. When idling the rev counter shows 2000 and then zero before the engine cuts.

One more think. My Haynes Manual refers to the two sensors as Crank Speed Sensor, and Cam sensor.
The Crank Speed Sensor: "2. Unplug the crank speed sensor wiring from the harness at the connector, which is located in the engine bay behind the battery" 4. Unscrew the retaining bolt from the bell housing. Recover the spacer where fitted"
The Cam sensor: 6. "... Not that the sensor is located at the front of the engine, on the left hand side of the timing chain sprockeet"

Surely what you guys refer to as Crank posistion sensor is what Haynes refer to as "Crank Speed Sensor" right? And this is the one to test/replace. Is it possible to reach it from above? I dont have any garage facilities so I have to do it just parked in the street.

Pop your hood and look for your ignition control unit. It would be just behind your abs module, towards the driver cabin. The crank sensor is the plug that is coaxial. Unplug it and test the inside prong to the outside (continuity)

All this can be done in five minutes on the side of the road.

Sounds a lot like a crank position sensor issue to me. I had to replace it on my 300E when I had one....it caused stalling issues. Although later on it developed other stalling issues even with an ok CPS. I suspect most was due to a very degraded wiring harness on the engine.

Ok. Purchased a new cps today. Didn't sees to bad a job. And although it was riddiculously expensive it's another thing to rule out. But now it seems like I've ran into this problem m103 Crank Position sensor removal and replacement - Mercedes-Benz Forum
Got the bolt out, and the sensor seems to be moving, but it doesn't come up. As the sun was setting and it is cold (3-4 degrees) I quit for today. And then also either i teared another wire while jiggling around or at least I found a loose wire.
All in all a bad merc day here in Oslo. ...to be continued...

I have been experience exactly the same problems with my M102 engine.

One symptom that I also noticed is that sometimes when turning off engine but keeping key/ignition on the tachometer makes same jumps all the sudden and the fuel pump starts for a second. This is usually at operating tempature, about 80 degrees celsius

For all I can understand is that something is triggering the fuel pump relay briefly. Could a faulty CPS trigger this? I did measure it with a multimeter but it's within specs. Same goes for the coil.

My car is regularly maintained and plugs, distribution cap and rotor and wires have been changed. Well since I already drove the car my first 100 tkm perhaps it's time to change them again.

My car got worse. After standing still for a week it wouldn't start at all. 2 things I did: I had just replaced my fuel pump relay. Turned out it was wrong. I jumped two plugs on the relay and it almost started. Then - I was absolutely sure the distributor cap was fine. It only had some 30000 km. I replaced cap and rotor anyway and since then it has ran perfect. CPS? I gave up

Sorry I saw this too late. CPS unlikely on these cars but all HT must be in perfect state with highest quality parts.

I'm glad it's running well now.

RayH

My brain is not working- "HT" means what? I'm having similar issues with my 91 300TE. I replaced CPS but no change. Intermittent no start when cold, intermittent stall at operating temp, almost never restarts unless engines cools down somewhat. Thanks,

In my case, it was the distributor rotor. Again, make sure all distributor components are of the highest quality and clean.

HT=High Tension. Coil, Leads, Cap, Rotor, PLugs. Ensure that all are of the right quality and in fine condition.

RayH