Fuel Injectors ???? 92 500SEL
 

1992 500 SEL - Starts fine..idles fine..revs fine in neutral initially...until warming up or driving about three miles...then starts missing and sometimes stalls. If stalled, often won't restart until it cools down ....30-60 minutes. Did not drive in winter but started periodically. Local "general" mechanic says injectors are problem. HELP...he wants to pull and clean for $600....Go for it??? Or are there other culprits...fuel pump, relays etc.???

I can't point you in a direction, but if it cold starts and runs okay for a few minutes, I don't think you need to spend $600 for "injector cleaning".

If you store your car during the winter, change the oil just prior to storage and charge the battery monthly or leave a battery tender on it. Starting a car to "warm it up" during winter storage is harmful. Many studies have documented that about 80 percent of engine wear over the life of a typical automobile engine occurs during cold start and warmup, so don't start it unless you want to drive it. The engine will have more than enough oil in the bearings and elsewhere to provide normal boundary lubrication during cranking and until the pressure comes up.

The clock does not run on fresh oil in the crankcase during winter, so you can drive it the full time or mileage interval after it's been returned to service, and doing this pre-storage oil change is very important as dirty oil during storage can cause corrosion damage.

Duke

Thanks, Duke, for the advice. I did drive on good days and didn't let just idle. Any ideas on the problem...I didn't like the injector analysis since it starts and idles fine after a long rest...or anytime.Only after running a while does the missing and stalling occur.

Like I said, I can't steer you in a firm direction, but thought the injector cleaning was a crock. An injector problem would likely cause symptoms both cold and hot.

I'm still trying to figure out the mysteries of the KE fuel injection system - probably one of the most complex fuel systems ever built for an automobile engine. It's essentially a complete mechanical AND elecronic fuel injection system in one. The Germans leave no stone unturned!

Based on experience I have with some EFI systems I'd recommend you look at the KE engine temperature sensor. I don't have any specs for it, but maybe someone else does. I recall reading that it's an inverse coefficient thermistor - resistance decreases with increasing temperature, so you could check its behavior hot and cold, and if it's either open or shorted, it's probaby defective.

I have some experience with a rather esoteric Bendix EFI system where an engine temperature sensor failure will keep telling the ECU that the engine is cold, so it never goes off cold enrichment. Operation degrades as the engine warms, and hot restarts are difficult/impossible due to flooding.

Duke

Since the problem occurs only when the car is warm I would first look at coolant temp sensor. It is VERY capable of creating problems youre describing.

Thank you both very much...it does seem that it is a sensor problem since it runs FINE when cold...I assume that engine and coolant sensor are same thing???? I'll get it checked and keep you posted. Looked it up on net and found for $26...goes in intake manifold with 4 pin plug...hope thats it.

hang on a minute....

you have a 92 500 SEL right? To my believe its a W140 early model.

Your temperature sensor should not be the 4 pin plug as that is the one for the later models.

There are 2 sensors that go into the thermostat. One of them is a single pin sensor while the other is a 2 pins sensor with blue color on the base of the pin.

The single pin feeds to the cluster to tell you what temp is your engine.

The dual pins feed to the A/C module to tell the car what temperature it is and when to turn on the aux. fans. It also tell the A/C if emergency shut off is required.

Which one you need to worry about? I think there is a 3rd or even 4th sensor which geeds to the car main computer which adjust fuel mixture etc etc etc.... That is the sensor you should be worried and not the CT and ECT sensor I just described. (they are cheap and if you are worring, go for it too)

hope this helps. I am sure others here can tell you more.

I have posted pic of the sensor before. Even better, look for Jimf homepages and he have a whole series of information regarding ECT / CT sensor

cheers

I would replace the fuel filter 1st.

How does FF affect running conditions when the car warms up?

Filter not allowing the correct amount of pressure into fuel system

Seems to me that if during the cold conditions (enrichment) the car runs OK - that proves that there is sufficient fuel flow. When the car warms up it uses less fuel.