Hello gurus,

I've spent quite a bit of time wrenching on older diesels, but I'm pretty new to the M104's.

I've searched the archives, and seen a lot of discussion about misfires on the M104 engined W124 E320's, but nothing that really seems to address my problem.

Car is a 1995 E320 with 155Kmiles. Car misses at idle when warm, and sometimes will hesitate on acceleration. Once things get above idle, or the hesitation stops, everything is good to go. Runs smooth at speed, and gas mileage seems to be OK.

Engine wiring harness is only about 25Kmiles/3 years old. All spark plug wires have been replaced. Plugs are the correct non-resistor BOSCH's, and I've double checked the gaps. I have built Arthur's code reader tool, and have pulled the codes several times. After replacing an obviously bad oxygen sensor, it looks like I'm left with only one recurring code. I'm still getting a code 11 on pin 14. Does this sound like the electronic throttle actuator wiring issue? Anyone know where in the FSM the holy gods of Mercedes have outlined R&R of said beast? I see lots of CIS stuff on the CD, but not much mention of the HFM system. Could it be a bad coil or two? Not sure how to test these short of throwing parts at it. I do have access to an oscilloscope, and could probably cobble up an inductive pickup, but I'm not sure if this would allow me to "see" the miss...

Any help would be greatly appreciated. Thanks.

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Gary Thompson
Georgetown, TX
1995 E320
1984 300D

The first thing I would try is the spark plug connectors under each of the three coils. They fail commonly and will cause a misfire or hesitation. I think they're about $5 each or something like that. I notice you said you replaced the spark plug wires, but as you didn't specify the connectors on those three cylinders, I thought I'd mention it. Some kits don't include the connectors.

Jonathan

Jonathan,

The plug wires, including the connectors under the coils, were the first thing I tried. Got a brand new set in there, but it made no difference.

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Gary Thompson
Georgetown, TX
1995 E320
1984 300D

I just wanted to make sure. I saw that you did the wires, but you didn't specify the connectors and the wire sets don't always come with the spark plug connectors. The Bosch kit has them, but with the other kits require you to buy them seperately. I was crossing my fingers that it was a cheap fix for you. I hope someone can point you in the right direction.

Car is a 1995 E320 with 155Kmiles. Car misses at idle when warm, and sometimes will hesitate on acceleration. Once things get above idle, or the hesitation stops, everything is good to go. Runs smooth at speed, and gas mileage seems to be OK.



Any help would be greatly appreciated. Thanks.[/QUOTE]

Hi -
Ignition coils are a common problem on these cars with higher mileage. They too, will cause a miss at idle or under a load.

Scope will show a misfire.
I would also tap the OVP while I had the scope on the primar..see if it drops power when tapped...

Thanks, Arthur. I'll take a look at the OVP and see if I can borrow a scope.

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Gary Thompson
Georgetown, TX
1995 E320
1984 300D

Had identically sounding symptoms and suffered for 2+ years while unsuccessfully trying out most things mentioned in various forums. Finally tracked it down to a very slight build up of oily cr@p inside the dizzy cap. Resolved it by a quick spray of a solvent called something like 'Electrical Contact Cleaner' and wiped round entire cap and rotor arm 'til squeaky clean. Problem immediately disappeared and hasn't returned (4+ months now!).

Someone once posted an explanation that the oily film coating the inside of my cap was probably vaporising at a certain temperature and somehow affecting the sparking. This was why my engine would idle perfectly from cold but with a kind of 'hiccup' as temp hit 60-70deg.

Hope your problem turns out to be something so simple, and you don't go through $$s (as I did) to find the answer.

Best of luck,
Neil

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Chassis in question has DIS ignition ... no distributor to be concerned with.