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'88 Mercedes 300E 3.0, '92 Mercedes 300D 2.5 N/A, '02 Volvo S60 2.4
20 Posts
Discussion Starter #1
Hello all. I am the new owner of two 124 Mercedes. I have an '88 300E and a '92 300D with a '87 190D engine dropped in her.
For the moment, my concern is with the '88. I'm having too many issues with the diesel and I need a reliable car ASAP. It seems more cost affective and less aggravating right now to fix the 300E. The trouble I am having is she's running like crap. A year ago I looked at this car and wanted to buy it but couldn't come up with the funds. She ran like a champ when I saw her then. A year later, she had sat up in "storage" and when I saw her again, there was a constant misfire and she would only run for about 15 minutes at a time until you simply could not crank her. Also, the exhaust is black and smells extremely rich.

I have done all that the extent of my knowledge and budget will allow me to do for now. Here is my list for short...

Compression test 170-175 each cylinder.
Drained the old fuel and replaced with new premium and added a double dose of injector cleaner.
Checked the fuel lines post fuel distributor.
Checked and ruled out any faulty plugs or wires.
New distributor cap and distributor rotor.
Changed the OVP relay.
Checked all the vacuum hoses for leaks.

The next thing I plan to do is to replace the 02 sensor.

Now, since I've done all of this, the misfire has gone from constant, to every couple of seconds but only at a cold start. Once I run it and let it warm up just a little bit, it almost smooths out. But after it's at running temperature, the idle drops from it's normal 600ish to 300 and starts to die.
The throttle also seems very unresponsive at all times.

I am at a loss.
I had noticed one thing, however and this is my primary question, other than asking for advice on what else I could try. I thought the ECU may have gone bad because despite the fact that I have all of my fluids and the battery is charging, all of my warning lights on the left of the cluster are on. Battery, coolant, oil, etc. On my search for a new ECU, I noticed the one I have seems to be from a 260E. A 2.6 (103.940) engine and mine is a 3.0 (103.983). The part number is "005 545 72 32". Would this ECU be installed originally, or has it been replaced with an incorrect one? And if so, might replacing this with the proper ECU fix my issue?
I've called my local Mercedes dealership and I've given them the vin, but they have yet to get back in touch with me.

Thank you in advance, everyone. I do apologize for the long post. Please be gentle. :bowdown:

'04 W211 E240, MY10 W204 C300
825 Posts
A 2.6L ECU will work quite well with a 3.0L engine. The main difference being the fuel injection mapping at high rev's i.e. should not be an issue. The ECU's and EZL's were different between the 2.6's and 3.0's but not really so such.

Misfires are 99% electrical. Make sure your plugs are non resistive types.
Put the car in a garage at night. Turn off all the lights and start the engine, Check out the leads, plug ends and distributor ends and make sure there are no leakages anywhere.
Make sure your distributor has no cracks in it.
Check all engine rubber hoses for cracks or leakages. (your vacuum gauge should be near enough fully to the left at idle in park).

If you haven't done it yet change the fuel filter where the pumps are and at the inlet to the fuel distributor.

I would be checking your CPS resistance at the EZL end. This is the green wire with the CO-AX connector. It should measure between 850 and 1100 ohms cold and hot.
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