W124 M103 stalling engine
 

Please help, I need ideas.

Subject: 1987 300E, W124 chassis, M103 engine.
Problem: when cold, starts without issues, no misfire, runs smooth as can be, like it's brand new. Can rev the engine, drive it around the block, works beautifully...until it gets warm (>80 degrees C). As soon as it gets to running temperature (about 20 minutes), it chokes, stalls, and dies. Then while still warm/hot, it will not restart. Engine turns over (starter turns it over fine) but engine will not catch. Not until it's cool again. One hour later when cooled down, starts up and runs like new again.
Thinking it's a failing camshaft position sensor? But I reliably get 800-900 Ohms. Should I still just replace it and see what I get?
No fuel smell, no leak, I feel like I'm chasing an electrical gremlin.

Took it to a relatively young mechanic who couldn't figure it out and just gave me my car back.

Help! She's too nice to part out.

Thanks.
Cam

Get it to stall out. Dump some gas down the throat of the air intake and see if it starts. If it does, it's a fuel problem. If it doesn't, it's an ignition problem. There's a laundry-list of possibilities it "could be", but focusing on anything prior to doing some very basic troubleshooting is a waste of time.

Added ether down the intake after it stalled one day. No change, still wouldn't start until it cooled off.

Check for spark remove coil wire hold it 1/4 away from ground see if you got spark, check cap and rotor, check overvoltage protection relay, remove airfilter depress airflow meter with someone cranking , should feel resistance or and hear fuel flowing chirping, depending on these basics cause could be a lot more things, test to see if fuel pumps are getting voltage

Did it even try to fire? Burps or farts? If nothing at all, it's an ignition issue of some sort.


Start with the OVP relay as suggested above. They have a habit of going belly up in random ways and it's a good idea to replace with a new one if it's even suspect.


Next would be to check for spark from the coil wire going to the distributor. If you have spark there, but no spark at the cylinders, time for a new cap and rotor. If no spark at the coil wire, you could have a bad coil, bad crank sensor, or bad EZL.

OK, a couple simple things you need to do before replacing anything......

You’re probably referring to the crankshaft position sensor, your car doesn’t have a camshaft position sensor.

Since your issue is predictable, try this first.

Unbolt the EZL/Ignition Module and apply some dielectric paste to the contact surface between the inner fender and the bottom of the module. This acts as a heat-sink to prevent the module from over-heating. I know it sounds crazy but I’ve seen this work many times when addressing an issue like yours.


If this doesn’t fix the problem take a look inside the distributor cap. A toasted rotor contact may be the problem. Also check the routing of the coil wire. If it’s touching something on it’s way to the distributor cap it may be arcing. Again, it may sound silly but I’ve seen this happen countless times.....

Mine was acting in a similar fashion, great cold, loooong crank hot to start and then stalled.

X2 on what ILUVMILS said, it was the distributor rotor.

Good luck!!!

Could also be an issue with the coil when it gets warm. My M103 drove me nuts with stalling issues. I finally got it running decently well but it would still stall at complete random, so I ended up selling it. M103's seem to need every component in absolute tip top condition or they will torment you with weird issues. My 1 year older M116 was dead reliable in comparison.

When did you last replace your HT leads, spark plugs distributor cap and rotor .If the answer is dont know then start there first .If it is still the same then go on to fuel supply .

Thanks for your input! Let me start with some of those suggestions and get back to the group. Keep you posted.

Divide your problem into 2 ways is it a fuel problem, or ignition/electrical fault, if it still dosent restart even when adding a little fuel down the airflow meter concentrate on ignition fault report back

Cam, as far as I know it's thermal paste that you want to make sure is under the EZL so the inner fender functions as a heat sink. If the EZL fails a new one from your local MB dealer will cost in the neighborhood of $1,500 to $2,000. It's important to avoid that scenario by conscientiously maintaining the ignition system components (distributor cap, distributor rotor, ignition wires, coil and spark plugs).

Well...not the CPS. And not EZL overheating. Replaced the CPS and applied thermal heat compound under the EZL. No change. New symptoms though that may (or may not) help. Rough idle and dying occurs now when in gear. Can get it to idle in neutral or park, but put it in reverse or drive, starts to sound like it's not firing on all cyclinders. Maybe start with coil, plugs, and HT cables, huh. Unless anyone else has an idea?

Have you inspected the cap and rotor?

CPS and EZL are most unlikely with those symptoms.

Start simple and cheap. Spark plugs (non-resistor Bosch, Beru, NGK), distributor cap, leads and rotor - MB original is best, followed by Bosch or Beru - sadly, quality from Bosch and Beru is not improving. These engines love 100% HT systems.

When you're happy that HT is good, move on to the fuel system.

RayH