1986 300E spark issue causing stalling when hot - PeachParts Mercedes-Benz Forum

mdg404 · #1 07-19-2007, 09:51 PM

My son just bought his first car a 1986 300E on Ebay. We picked the car up and 15 minutes later the car stalled out and would not restart. The owner did not reveal this issue. What we know is that the stalling issue is due to loss of spark when the hot. the following parts have been replaced REPLACED INNER/OUTER TIE RODS ON BOTH SIDES. NEW PLUGS, OIL CHANGE, FRONT FLEX DISK ( LIKE UJOINTS FOR DRIVE SHAFT ). THERMOSTAT, RADIATOR HOSES, COOLANT FLUSH, DRAIN & REPLACE POWER STEERING FLUIDS,(2) NEW TIRES, TEMPERATURE SENSOR SWITCH, FUEL INJECTOR SWITCH AND FAN CLUTCH, Fuel pump and filter. It is at a mechanic that specializes in Mercedes and he has determined it is a spark issue and that it is not coil, distributor, rotor, ignition module. Can someone help us out it is my son's first car and he has used up most of his money.

thanks

Benztech · #2 07-20-2007, 01:48 AM

Did you say you have no spark? I dont see any mention of the crankshaft position sensor in your comments. Its easy to check it. At ignition module connection check for a resistance reading of 680-1200 ohms at cable going to sensor.The other thing is the overvoltage protection relay mounted behind the battery it has a fuse on top of the relay. Also those plastic fuses in the fuse box cause all kinds of problems take a good look at them too!
good luck Tim

wscheffer · #3 07-20-2007, 06:11 AM

It sounds more like the Ignition Control Modual (EZL) is faulty. Check the crank shaft position sensor to be sure, but I think that the previous owner knew it was the EZL. Being that it is such a costly part they sold the car verses fixing it.

Try ebay for a good used one if you need it. A couple hundered verses a couple thousand. Just make sure who ever you buy it from will guarantee it to be in workable condition.

Hope This Helps!

gmercoleza · #4 07-20-2007, 10:36 AM

Agree - sounds like either the EZL heats up and cuts out ($$$$$$), or maybe the CPS.

mdg404 · #5 07-20-2007, 11:24 AM

Quote:

Originally Posted by Benztech

Did you say you have no spark? I dont see any mention of the crankshaft position sensor in your comments. Its easy to check it. At ignition module connection check for a resistance reading of 680-1200 ohms at cable going to sensor.The other thing is the overvoltage protection relay mounted behind the battery it has a fuse on top of the relay. Also those plastic fuses in the fuse box cause all kinds of problems take a good look at them too!
good luck Tim

The loss of spark happeneds when hot. Thanks for the help.

brewtoo · #6 07-20-2007, 11:24 AM

I know you said it's not the coil.

But are you SURE it's not the coil?

david s poole · #7 07-20-2007, 11:37 AM

unless you can verify that the crankshaft position sensor has been replaced it most likely is your culprit.this sensor tells the ignition module where top dead centre is and without this info no spark.and it works when cold and then dies when hot is classic symptom for this sensor.

ILUVMILS · #8 07-20-2007, 12:26 PM

Quote:

Originally Posted by david s poole

unless you can verify that the crankshaft position sensor has been replaced it most likely is your culprit.this sensor tells the ignition module where top dead centre is and without this info no spark.and it works when cold and then dies when hot is classic symptom for this sensor.

If we were talking about a newer MB I'd agree. The older MB's have a much more durable sensor, and because of the way it's mounted, isn't as susceptible to engine heat.

mdg404, try this. Use a heat gun on the ignition module to rapidly warm it up. See if it stalls out sooner than if it were to be left alone. If it does, you may try applying some dielectric grease to the mounting surface of the module. This is a simple, cheap, and definitive test, and it may buy you some time to shop around for a deal on a replacement unit.

saumil · #9 07-20-2007, 03:38 PM

Also check the wire from the coil to the distributor and the wire from the crankshaft position sensor to the ignition control unit. They pass thru areas that are subject to high heat.

One of the pins from the coolant temp sensor ends up at the ignition control unit. Make sure this signal is arriving at the ignition unit. Though I dont know how a loss or a wrong signal could completely take the spark away.