90 300SEL Keeps stalling, hard to start
 

OK, my 90 300SEL suddenly developed a problem, It starts when cold, runs perfect for awhile then stops. Very hard to start after that. I have changed the Overload Protection Relay, It is not plugs,wires or anything like that. (if it was it would work like crap all the time) It is getting fuel pressure, new filter, pump works fine. changed fuel pressure regulator, I am stumped. cold start valve? I just don't know what is up. Any idea's?

Check the Crankshaft Position Sensor.

I never thought of that! Can it be tested or just replaced?

CPs will ohm out good around 1100 ohms. Do a quick google search to verify the exact.

Problematic hard warm restarts can usually be traced back to a worn distributer cap and rotor. Do research and diagnose or just throw money at it.

When was the last time it had a tune up anyway?

It has been years since a tune up but it has not been driven hardly at all. The problem actually started suddenly. Most tune up problems are all gradule thing, I have looked at the cap and it looks good. I think it is something such as a sensor or of that nature.

I have a M103 in my 86 W124. I have had occasional bouts of that stalling and hard to start following the stall. I have found that by immediately, (or as soon as I could get a can) to put a can of fuel drier in the tank. Immediate relief. Mine seems to want to go through that stall/ no start about once a year. Outside of that problem, it is perfect. My choice is "STP" deicer or water remover.

Please do all us m103 owners a favor and please tell us what ended up being the culprit.

I will, I am going to change FP relay first

It won't cost you a dime to look at the distributer cap and rotor for burn marks. Just saying.

your right it won't and I will look at it.

Well, I took the cap off and cleaned it up until I get a new one, seems to be running fine. I can't hardly believe the cap would give so much trouble. I could believe poor performance or hard start but no start until cool down? whats that about?, just glad it's going tho.