jjay911

OK Well I have put 25000 miles on my car over the last 2 years and I have really enjoyed the car. My only complaints are that the seats are not good for long trips.

I experienced a random miss fire about 6 months ago to find out I had the wrong spark plugs in the car. Replaced them and the problem went away. Then a month later one of the coils went out so I replaced it. IT was also causing a random miss fire.

So last week she starts miss firing again. No check engine light on at all. I bring it into the shop and they are scratching there heads now.

Coil works.
If flashes a miss fire code when it is miss firing. But once you restart the car it goes away. Then when the car goes over 2500rpm it starts miss firing again on number 3 cylinder. It will only do this over 2500 rpms or when the car is driving on the road with a load on it. NOt at idle.

Not sure what the wiring harness route is going to cost me but I have plenty of Time since I have a lot of cars. I am open to advice or comments.. Thanks gang...

Current mileage reads 197,000 and its a 95 model.

DRBC43AMG

Search around on here as there is someone who made/replaced the faulty harness on his C36. I can't remember his name....

Looked around and I believe it was jumph4x

jjay911

Thanks I will look around... Hopefully more folks come forward...I will need all the help I can get on this one I am afraid... Thanks...

Super B

Hey I just fought a misfire code on my 36. Pull the offending cylinder coil an look at the resistor boot between the coil and the plug. Mine had formed an invisable crack were the boot goes over the plug and was allowing spark to jump down the side of the plug to the head. The leaking spark left small carbon traces down the side of the porcilen and that's what made me look at the boot. When I squeezed the end of the boot the rubber opened up and then ithe crack could be seen. Not saying this is your problem but something to check.

jjay911

SuperB,

Thanks for the response. Yes we checked that exact malady. After replacing the ends and coils the computer says that the car is not missfiring but once we go over 2500 it missfires. And cant figure out why yet... I will update later with more info on what it may or may not be... Thanks... I just hope it aint the harness....

jjay911

Well the Shop cant figure it out. 9 hours of diagnostics and numbers 3 and 4 cylinder go dead after 23 to 2500 rpms...

I think maybe source a good used Fuel Injection Computer is the next test. I had a similar problem on my SL a few years ago and it turned out it was my secondary Fuel Pump...Any thoughts??? We replaced wires and coils just to make sure and they are fine...

Super B

Sounds like a solid plan if you can find another known good PCM. Have you opened up the PCM and TCM box and looked in there? Totally unrelated but good chance to check for oil on the transmission controller anyway if the o-ring on the lower connector has gone south. How does the engine harness look? Sucks your fighting "those" problems where nothing makes since. Have you tried a different coil? Some times new parts fail. it's really suspicious that two cylinders on a shared coil are acting up.


Edit* never mind about the oil on tcu just saw your car is a 95.

jjay911

Well The shop has checked everything know to man on this and are stumped. The only thing I can do now is start throwing parts at it. Anyone know of any good source for FI computers etc... I found this on eBay but not sure if there are more than one computer I should check.

http://www.ebay.com/itm/370462166176...84.m1438.l2649

Or does anyone have a c36 they are parting out? Good thing I have other cars but I do want to eventually get this back on the road..

My number if anyone has ideas.. JJ 949-910-1206

nd4spd13

Whatdya need buddy?

jjay911

That is the challenge I am not sure. I guess I need all of the fuel and spark related computers. But maybe I just buy the car from you. I dont know. You have a phone number?


I still owe you a photo of the Prototype. I will text it to you if you give me a number..

jjay911

OK I am ready to buy some computers.... 949-910-1206

Jeff

Super B

Any news on this? did you source another controller?

nd4spd13

On the truck there now

Super B

Nice, The whole ride or just the controller? Really interested in the fix. On a side note I was driving for a week or so with the coil covers off getting around to installing new plugs. You don't want to leave the cover off. The engine started devolving a miss and a some what strange rattle only while in gear. Looking into it, the coils had worked them selves loose from the ground post and from shaking back and forth had rubbed a low spot into the threads on the ground post. This made intermittent grounding issues and a miss. Ended up turning the ground post 90 degrees and buttoning everything back up. But made me think jays problem. Of a rpm specific misfire.

jjay911

Hopefully when computers arrive we will have an idea.. IT may fix it it may not. The only thing I can tell you with certainty is about 18 months ago is when I started noticing this type of thing.

It all started one day when I was moving something heavy in my trunk and it shifted and crushed the Fuel Pump relay (that little green one in the trunk) From that day on I have had these issues. I replaced it with a new one from mercedes even though the numbers on it didnt match. I am not sure if that mattered but lets see how things go...

jjay911

Computers did not fix the car.. So its back to the old Drawing board.........I have this old time mechanic looking at it. He is the best at diagnosing problems so lets see how he does... So far no one has been able to pinpoint why number 4 is misfiring. Funny thing is as long as I drive like 20 miles an hour or under 2200 rpms it never fails.. Once I go over these thresholds she starts bogging down.

Any ideas?

Super B

Strange jay.. Really strange. I can understand it being rpm specific but the 20 mph thing. Being a 95 do you dont have a ASR switch in the dash do you? . Would be interesting to lift the car, get it on jack stands/block real well, pull the rear wheels for safety and put it in gear where you could analyize what's going on at that rpm/speed point. You guys have probably already logged the running data, how did you guys determine it was no. 4? Bad injector maybe?? I have another whole set of known good injectors that you can borrow if you wanna try that route.

Controller codes? Just a p0304?

jjay911

Yes there is a Traction control button on the dash. I have not checked injectors yet. But does that explain why the car runs great and even revs out in neutral or park but only under a load does it fail. The computer sais number 4 failure. When I brought it out to my other Mechanic, I had to drive it about 15 miles. The first 3 miles were ok on 5 cylinders. By the time I got 9 miles down the road the car was barely going 50mph. And when I took the exit the car shut off. I put it in neutral and restarted it. Then it drove great all the way to the mechanics and didnt fail again until about 500 feet before I pulled in....

Super B

Hmmm.. Have you hooked a gauge on the fuel rail and verified fuel pressure when it's under the failing condition?

What's the chances you have a fueling issue and starving the engine?

jjay911

Great Idea. I will remove the hood and jump on top of the car while the mechanic takes off..lol... Or is there another way

Super B

No more of lifting and blocking up the rear, turn off traction control, use the brakes to apply load and watch the gauge.

jjay911

OK this I will try....and I am sure it will do a cool burn out too

Super B

Well, just one of many things to check. Most likely your tech will track it down with good ol fashion data logging and trouble shooting. Strange problem. Hopefully he has an engine analyzer and can check spark and fuel signals through out rpm sweep. good luck buddy.

jjay911

SHE RUNS.


Yea you would never guess in a million years the problem. And maybe a preventative thing to check. Somewhere along the service time it appears that the connector to the computer for the wiring harness was yanked out hard enough to dislodge some of the Wires inside the female end of the connector. These wires turn out to be for the Fuel injection rale. So my Mechanic carefully repaired this and put me back on the road. 14 hours of Diagnostics and only 380 dollars charged... I am glad its over....

aaronirvin67

I have a cls 550 and I just got my bumper replaced when I dropped the car off there was no service engine light on when get the car back today I get a service engine light with the po 302 code cylinder 2 misfire. Where is the fuel injector rail located is in the front near the bumper because I think the wires where knocked lose during the repairs to my car. Do you have any advice