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Old 08-04-2004, 12:42 AM
Registered User
Join Date: Aug 2004
Location: Patterson, CA
Posts: 1
Unhappy misfiring, rough idle, poor mpg, undriveable!

Hello everyone, my first time here and I wonder if you can help!
I have a 1994 E320 that belongs to a friend of my wife. It is almost undriveable due to erratic idle, misfiring, occasional stalling. The car does drive smoothly on a very light throttle, but as soon as you try to give it more it starts to miss and drive very poor indeed.
Since I have had the car here I have replaced...
Engine wiring harness due to cracks,
Spark plugs,
Plug wires,
The three coil to spark plug connectors.
All of this to no avail! The CEL was on when I first got the car, giving codes 6 and 7, after clearing these and initially fitting only the new wiring harness I took the car for a ride into the hills using the "drive it like its stolen" method. It still drives very poor with poor idle and is now giving me the codes 22 and 23.
Any help would be greatly appreciated!

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Old 10-20-2004, 02:43 PM
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Join Date: Nov 2001
Posts: 1
Thumbs up Misfiring

22 cam position sensor signal defective.
23 Intake manifold pressure w/ engine running too low.
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Old 10-20-2004, 07:33 PM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Bad airflow sensor will give you fits on those cars, too -- idles rough, misfires terribly at large throttle position, but runs well at speed.

Check all the connections, particularly the manifold pressure sensor and the cam position sensor, they may be loose or incorrectly installed.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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Old 10-20-2004, 08:45 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,804
Clear the codes and retry.
Also check for false air anywhere from cross-over pipe.

Would be cool if you had codes from HFM module { pin 8 ]
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Old 10-21-2004, 12:47 AM
benzdude's Avatar
Registered User
Join Date: Sep 2004
Location: Denver, Colorado
Posts: 20
ECU Fried

I recently changed the engine wiring harness on my '93 300E due to problems similar to yours, but worse (car ran rough, lost power, and then eventually died and wouldn't even start). After putting in the new harness the problem was fixed, except that cylinder no. 4 would not fire because the fuel injector was not getting a signal through the harness (cylinder had spark and fuel injector works fine in other cylinders; I swapped the no. 4 and no. 1 injectors). After exhausting all other possibilities, I finally took it to an independent Mercedes shop and about $200 later they said the short circuiting from the old harness had probably fried the ECU since no signal was coming out of the ECU for the cylinder 4 fuel injector. They called the ECU "HFM control module" (it's the same box behind the battery that the engine wiring harness connects to). I've ordered a remanufactured ECU which I'll get this friday. I'll keep you posted on whether or not it solves the problem.

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