Issue after wiring harness replacement on a 94 C220 - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 02-22-2016, 12:18 PM Thread Starter
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Issue after wiring harness replacement on a 94 C220

Hello Everyone,

I hope someone might be able to lend some insight to my issue. Iíve also included some diagnostic info the might help in deriving to a solution.

Over the weekend I replaced the main wiring harness on my 1994 C220Ö The reason in doing so was two fold... #1 There was a short in the cable going to the MAF sensor, thus I originally replaced that, but in doing so I noticed that when I peeled back the fabric tape going into the main coupler that connects to the ECU, that those wires where becoming exposed due to the coating on the wires cracking and falling apart when touched. Despite my best efforts to apply heat shrink to the now newly exposed wires before putting everything back together, a few of these exposed wires must have still touched internally in the reassembly process. After reconnecting the coupler to the ECU, reconnecting the battery and starting the car, there was electrical arching coming from under the newly taped area going into the coupler. Thus reason #2 , a this point a new wiring harness was the obvious course of action.

Once I installed the new Mercedes Benz manufactured harness, (not a third party harness) and all of the fitments matched up perfectly. I cranked my car here are the symptoms that I am experiencing:

- The car starts hard.

- It idles very roughly almost like it's running on 3 cylinders and wonít hold an idle unless you manually keep your foot on the accelerator, once you let off it stalls.

- This car has never produced any real visible exhaust smoke, but it does now when I rev it to prevent it from stalling.

I replaced the MAF sensor a few years ago with an OEM Bosch, (I accidentally dropped it while cleaning it and it was damaged) so up until the detection of the short in the MAF cable, the MAF sensor worked perfectly.

I have double and triple checked all of my connections both electrical and vacuum, and everything looks in order. I do own a scanner, and it is not throwing any codes, plus the check engine light is not on yet, this might be because the battery was disconnected for an extend period of time and the ODB memory has not had a chance to fully propagate.

My gut tells me this is an MAF Sensor issue, that it possibly shorted out due to the electrical arching when I attempted to fix the old wiring harness, is this possible? Can you fry/short out an MAF sensor? Is there a way to bench test a MAF sensor?

Thank You!
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post #2 of 10 (permalink) Old 02-23-2016, 03:09 PM
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Now this is a real headache. You have a hundred variables to run down.

But I would first start with the MAF. How does the car run when the MAF is disconnected. It should run better when disconnected. starting hard and smking is not usually a maf issue.

There are ways to bench test the MAF but you need to know the voltage mapping.
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post #3 of 10 (permalink) Old 02-24-2016, 07:54 AM Thread Starter
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Thanks for you reply.... When I disconnect the MAF, this is little to no difference in the idle. Is it possible for an MAF sensor to short out? I have a new Bosch MAF on the way, is there anything else that initially comes to mind that could be causing this?
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post #4 of 10 (permalink) Old 02-24-2016, 08:52 AM
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Since this happened right after you replaced the harness, it is most likely an electrical/sensor issue. Sorry nothing comes to mind. These harness issues are truly a headache. Hopefully someone else can come up with a diagnosis.

MAF sensors don't short out. but since yours is a glow filament it is conceivable that somehow too much voltage was sent and it burned the filament. still an unlikely event.
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post #5 of 10 (permalink) Old 02-26-2016, 11:52 PM
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Doesn't sound related to the maf to me. Sounds like a vacuum leak maybe. Did you have the intake manifold off? What condition is the OVP relay in? Still, I would try to get the car running better with the maf disconnected for now, and wouldn't jump to replacing it right away.
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post #6 of 10 (permalink) Old 03-03-2016, 05:43 PM Thread Starter
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Hey Guys,

Thanks for the helpful replies. I have an update: I went ahead and ordered and installed a new MAF sensor, however that did not solve the issue. I will say my car does run better with the MAF sensor connected versus disconnected. (Disconnected I can barley get it rev past 2,000 RMPs) I did check each of the spark plugs and found that plug #3 was very wet while the others where just barley moist... so I'm thinking that I could have an electrical/coil issue with the 3rd plug slot. Does this sound like it could be the cause?
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post #7 of 10 (permalink) Old 03-03-2016, 05:47 PM Thread Starter
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BTW CooperDeer... I did not take the intake manifold off... the OVP seems okay on the outside (famous last words) the 15a fuse is not blown.
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post #8 of 10 (permalink) Old 03-06-2016, 06:20 AM
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There you go, hunt down the issue with cyl #3 . Either it's not getting spark or the injector is stuck open (or shorted open). Test for spark on that plug first, if you've got spark maybe the injector was shorted out. You could always try swapping parts around to see if you can get the issue to follow to a different cylinder.
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post #9 of 10 (permalink) Old 04-19-2016, 03:32 PM Thread Starter
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CopperDeer,

You were kind enough to reply to my wiring harness issues a few weeks ago for 94 C220. I did some initial trouble shooting since then and decided to replace the second coil the one that provides juice to plugs 2 and 3. I also installed a new coil wiring harness while I had everything disassembled
as the original one was really decomposing and frayed. Now I have encountered a new issue after I put everything back together. Only the inside port of each coil (the one closest to the engine block) sends a strong charge to the plug. The outside port sends a very weak charge. Before I installed the new coil and wire harness at least i got a strong charge out of both ports on the first coil the one that goes to plugs 1 and 4.

Are there any relays or amplifiers (so to speak) that I need to be looking at?.. I am at a real loss.

BTW I grew up in Sylva, NC and went to Western Carolina, (please don't hold that against me... LOL) I've been to Boone countless times.

Thanks,
John
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post #10 of 10 (permalink) Old 04-28-2016, 11:25 PM
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Did you touch the throttle body wiring too? It looks like some problems on the throttle body.
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