1994 C220 Petrol random misfire

[Brasso]

Hi Guys

sorry for the first post being a problem post, I am desperate for an answer and cant either think of the right keywords in search or I have an original problem that nobody seems to have.

I bought the merc about a month ago, all was well noticed it had a hunting at idle problem, so replaced the MAF, not a lot of difference but it was a cheap one so didn't think much of it, the next problem I got was misfire on cylinder 2 and 3 but random if I restarted the car a couple of times it would run on 4 cylinders, the problem got worse so I did some research to find the dreaded wiring harness, so I spent a weekend taking the harness off and rewiring the whole harness, refitted, started the engine, ran perfect even had more power, I was really pleased, next day I decide to start the car up connected to my laptop as a diagnostic cable I bought had turned up, plugged it all up started engine ran sweet, cleared the faults still runs well, turned off, restarted the engine....2 cylinders, restarted again 2 cylinders, ignored the car for a day started engine, 4 cylinders, ran it for 100 plus miles ran perfect next day 2 cylinders.

it seems really intermittent on running on 4 or 2 cylinders

any help will be very appreciated

Many thanks in taking the time to read this

[Vetruck]

Your coil packs run two cylinders each. pack #1 runs plugs 1 & 4, pack #2 runs plugs 2 & 3.

I am having a weird issue myself right now. Have had a misfire a few random times. I changed plugwires (basic 101) and the problem went away for a week, but has returned once again randomly 2 days ago. I have not had any codes but suspect mine is either a coil going bads or yes the dreaded wire harness going bad. Keeping my fingers crossed on either since the coils are a pain in the ass to get to. (My car also a 1994 C220). My problem seems like 1 cylinder dropping though, not two. I have a feeling I may have a bad plug that acts up . I replaced them with high end Iridium plugs about 3000 miles ago but if it happens again I will change those back to standard plugs to see if that is an issue.

[Brasso]

Sorry I forgot to mention I replaced the coil pack for cylinder 2 & 3 which is what lead me to the harness, I have a hunch it could be a dirty electrical connector or a blocked injector which the ecu sees and is killing the spark to the cylinders to prevent damage? Could this be possible?

[Vetruck]

As much as I know cars and engines, I have not a clue about ECU's. I am getting a random thing as well which leads me to believe it is my harness starting to show signs of failure. THis is not acting like normal engine problems- something more computer/wiring related. Mine comes and goes and has different levels of trouble like as if the car is missing- yet runs fine most of the time in between random showings.

[Vetruck]

I am going to change plugs in the car tomorrow (My #4 plug looked a little dirty compared to the other 3), and if that fixes any random act up for a week I will leave it be, otherwise I will be buying an engine harness just to nip that in the rear since I have no plans to ever sell this car.

[Vetruck]

Just to update you with my problem- since it sounds coincidentally very similar and the same time frame- Mine turned out to be a bad #4 spark plug. I put very high end Iridium plugs in the car less that 6 months ago and my first reaction was to change plug wires since that was never done in 3 years ownership. Turns out the wires did nothing and I still had the problem. For kicks I simply changed plugs to be safe and YES it turned out I had a crappy spark pug. I am back to good ol copper Autolites. people can take those fancy platinum and iridium plugs and shove 'em. Ill stick to my trusty autolite work horses for now on.