300E warm startup problem, quits...
 

Problem with 1989 300E, when restarting (engine hot-warm) engine fires up as normal with no problem, and quits within a second or two as if no more fuel.

Try restarting again and the same thing happens. However, wait an hour or more and will start and run OK. Starting when cold, and it fires up and runs OK.

-So, not a problem with starting, engine fires up OK.

-Keeps on running after startup, if cold.

-Quits after startup, if warm.

-Let it cool and it fires up and runs.

Will replace the fuel filter, check connections and lines.

Anyone have experience with this problem? Any troubleshooting suggestions? Any help would be appreciated.

Thanks.
Chuck

Chuck:

Check the vacuum lines, and the hoses on the idle control valve (under the air filter housing). You will also have to check for other vac leaks such as a bad brake booster.

What is happening is that you have a vac leak, most likely, and also a sticking idle control valve. Engine starts OK, but the idle valve closes and then doesn't open fast enough. Usually a result of dirt from a leaking hose -- I've seen several of them split recently along the seam.

It is also possible you have a bad fuel pump relay, causing the fuel pressure to drop off -- it may run OK while cranking, but go intermittant in the run posiition. Outside chance it's the keyswitch too -- if wriggling the key makes the problem go away, replace the switch.

My money would be on the vac system, most likely a split idle control valve hose -- I'm working on that on the TE right now!

Peter

Thanks for the reply, Peter. Will check the vac lines, leaks and the idle control valve. Sounds like a good place to start.

Specific to the cause of this problem... What controls fuel flow after startup, when engine is warm and/or what would cause the fuel flow to stop after the initial startup fuel delivery... and why only when warm? No hesitation or sputter, just a clean quit. < Like when Grandpa turns out the porchlight!! >

Wait a darn minute...could this be electrical?...ignition?

BTW..new plugs, ignition wires, rotor, cap, less than 5000 miles ago. Checked today and all are OK .

Chuck

Check the condition of the coil.

When the engine is first started, the mixture will be in open loop control mode (fixed) and the idle control valve will be wide open. Once the engine starts, when warm, the mixture control mode will go to closed loop (controlled by oxygen sensor input) and the idle control valve will close momentarily to slow the engine down.

If the mxiture is too lean, the engine will promptly stall -- hence suspicion of a vac leak -- and if the idle control valve is sticky, it won't open up again fast enough to prevent a stall, worse if there is also a vac leak.

Does it occasionally stall when coming to a stop, particularly a rapid one? If so, sticky idle control valve for sure.

Peter

If you want to rule out the o2 sensor unplug it (under passenger carpet) or the EHA (back of fuel distributor) to rule out all fuel computer electrics.

OK...Sorry for the delay. Here's an update. Installed new O2 Sensor this past weekend. Problem seems to be fixed! Warm engine starts and keeps running when warm.

Only issue now is that the idle is a little low at 500 RPM. Feels better at 700 or 800. Will try to correct this. Any suggestions on making this adjustment?

Thanks everyone for your helpful comments.

Chuck

Vac Leak
 

I thought for sure it was a vac leak, too as these cars are known for that usually right by the air cleaner.

Where is the O2 sensor located?

Under the front passenger carpet there's a black bullet connector.
O2 is on exhaust pipe directly under the shift lever position.

Wire to O2 passes through tunnel wall from black bullet connector under carpet.


..

Classic symptom of leaking fuel injectors.

They're not holding pressure when engine is off, and engine is then flooded.

Start with accelerator open to verify.

Throttle valve
 

My 300SE is in the garage with almost the same problem.It starts ok when engine is cold but cuts out and does not restart when warm,and rpm is not stable as it surges up and down.I was told only this morning that the throttle valve needs to be replaced and the whole thing cleaned.It is at mb dealer in my area and will cost £300 to replace. I gave them the go ahead and have to wait until wed 23d to find out.Hopefully this will solve my problems with the car for a whole year and after £850 paid for parts that the car didn't realy need.Stay tuned.Will post result same day or after:dizzy2:

Can someone specify exactly where the M103 is prone to vacuum leaks?

IT'S FLOODED.

INJECTORS ARE LEAKING.

Try starting with throttle half to full way down to verify. (obviously let off as revs rise).