C240 Misfire
 

Hello all. I have read numerous posts with similar issues I am having but I figured I might as well post what's going on with my C240 before I go but parts to fix.

Current Mileage: 93k

About a week ago car was running great, I pulled into work shut off the car. About 3-4 hours later I go out start the car up and immediately after start it I get a CEL and the car is rough idling and it is 'missing' at all rpm ranges and it seems to get worse the longer the car is on after I start it. I take the car into a local shop here and hook it into the computer it is reporting a cylinder misfire on cylinder 5 and they want like 1000 dollars to do plugs and wires, naturally I say no thanks and pick up the car.

I am planning on buying some plugs first and installing them as it seems a likely cause and is fairly inexpensive to replace myself. First what plugs do you all recommend, should I get them at the dealer or can I just pick up some NGK iridium plugs and make sure they are properly gapped? If that doesn't work I was planning on doing either the wires or the coils next which do you all recommend I do first? Looks like the ignition coils are fairly expensive for this car and do I need to replace them all if I replace just one? Also how to reset the computer? I have heard turning the steering wheel left then right will reset it?


In any case just looking for some friendly advice from anyone out there that has more experience with this vehicle than I do. I appreciate and welcome anyones comments.

~cornic

First diagnose the problem, then we can answer appropriate questions. Number one. Go and swap the lead & coil pack on number five with another cylinder and see if the misfire code changes cylinder & replace all 12 plugs. Use Bosch originals. Then report back your findings and I will happily talk you further if necessary. Buy a 70 buck OBDII/CAN scanner from Kragens to read codes if necessary

BTW for Air filter removal see here
https://mbworld.org/forums/showthrea...88#post1227088

and for plug selection & replacement go here
https://mbworld.org/forums/c-class-w203/216940-diy-m112-spark-plug-r-r.html

BTW - where are you - complete your details please.

Sup Cornic,


Please read this post i had the same issue with my car.

And was quoted the same a little more 1300 dollars

For new plugs and wires so check it out

Like Glyn M Ruck Said Get a OBDII reader its your best friend

https://mbworld.org/forums/showthrea...198&highlight=

+1

wow
 

okay so i just read that whole thread it's almost shall I say, novel worthy, so many ups and downs, twists and turns etc. lol. After reading my problem is almost identical to yours. I think renting or buying one of the computers to reset and read codes is going to be the best approach. I honestly expect one of the following to happen however.

1. Bad plug(s)
2. Bad wire.
3. Bad gas (it did start happening fairly quickly after I filled the car up maybe 15 or 20 miles after a full tank of 91 from conoco phillips)
4. Potential MAF sensor is whack.

In any case I'm trying really hard to not let this stress me out and not go crazy and buy a bunch of stuff I don't need. I whole heartedly believe this can be fixed fairly easily and inexpensively.

Oh here's some more info I'm from KC MO, its a 02 c420 93k miles, my wife is the only one that drives it and that means it's my fault that it's broke. :D

Don't buy anything you don't need until we know what the problem is - you will need the code reader so get that & a set of plugs. Let's hope it is a coil, plugs, or lead. The MAF is an easy check. Just unplug it and drive on a default map - good luck :y

Just called auto zone I have them ordering 12 NGK plugs as speced in the Spark plug post NGK IFR 5 D 10. I've personally had better luck with NGK in the past. He also said they come gapped at exactly 1.0039mm or something so thats close enough to 1mm I'd say. :P They are going to let me put a deposit on a reader for 150 dollars which is full refundable so that's what I'll do. Then I can begin troubleshooting from there. Should I also go ahead and get some anti sieze and diecltric compound etc for tomorrow or just wait?

I guess my question is do I even need to buy the plugs at this point or can I just troubleshoot by moving the wires around etc? This also really pisses me off cause my mechanic charged me 100 dollars to hook into his computer when apparently I can do it for free ...... What a rip. But hey I guess I'm the real fool here not my mechanic.

Hey, listen - If you are happy with NGK that's fine - they make excellent plugs - I just know Bosch 100,000 Km plugs well - also pre gapped.

Get hold of that reader & start by swapping that coil pack & wires on no 5 with another cylinder & see if the code changes cylinder. The only reason I would get plugs is while you have everything off you may as well do them. What mileage have the plugs done?

I suppose you are right, and like you said I have nothing against bosch plugs it's just my experience with NGK plugs has been pleasant so far so no reason to change a good thing. In terms of when the plugs were changed I wish I knew. I personally have only owned the car for approx 10k miles and it did not come with service records :(. Like you said most around here seem to agree that plugs need to be done at 100k/miles anyhow so might as well do them. Will be picking up the plugs and computer reader tomorrow evening and then I have Monday off work so I'll begin working on the car. My dad let me bum his GLI jetta in the mean time so not all is lost :P.

Also I just have one of the 'standard' plug pulling sockets with the padding inside to grip the plug to pull it out and put it in and an extender for the wrench do you think this will suffice or should I do as the guide says and purchase a proper socket for the job? Just looking at the motor it doesn't appear to be 'that' difficult to get to the plugs. In any case thanks for the advice so far I feel better already.

Merc say plug change at max 100,000Kms or 4 years. I changed mine at 45,000 kms & 5 years after a few stuttering cold starts.
The proper plug socket makes life easier especially with the rear plugs. The plug change is not difficult but you will curse a few times - let's say I take mine to the dealer & watch but help friends with theirs - you go figure!!! The joys of a maintenance plan.

Don't become despondent, I'm sure that this is something simple - wires seem to become problematic at 100,000 miles & you are going to save a pocket full of money by doing it yourself - your dealers are not shy to charge. Let's just diagnose this sucker properly - we went around in a few circles with Kris's car. A case of too many very well meaning cooks spoiling the broth.

okay getting ready to go get plugs compound antisieze and reader now. gonna start working on it later tonight maybe or tomorrow. might need to figure out what cylinder is what cylinder im sure it's in the manual though.

They say it on top of the valve covers you can't miss it =D

Fair enough :D

Cornic, mark the coil packs & leads when you take them off so you don't mix them up. Kris had a neighbour disturb him & when he got back to the job could not identify which was which.

Okay I went to a few stores and got the following today:

1. 18mm open wrench
2. 12 NGK Plugs 1mm gapped
3. Swivel 5/8th socket adapter for plugs and an extender.
4. OBD II Reader
5. AntiSeize
6. Dielectric compound

Told myself I wasn't going to start working on the car until tomorrow, but I couldn't resist hooking up the reader to the computer. I received 8 total Error codes, some were duplicates. I listed all below:

P0306
P0303
P0305
P0302
PO304
P0300 -Multiple misfire detected.

I went ahead and cleared the codes and documented them. Going to take the car for a quick spin tomorrow and see what codes come back then go from there.

And good advice on marking where stuff is before taking it out :bow:

Please do, You have misfires on multiple cylinders - not just 5 - change the plugs - Unplug the MAF and drive on a default map & see what happens - We might have to check fuel filter. Do one thing at a time in logical order & check. I'm off to bed 3.10 am in the morning here.

Indeed I do have more than 1 misfire. So either the mechanic didn't give me the whole scoop or somethings have changed since they tested it. I will go ahead and do the plugs tomorrow, clear the errors and go from there. I will report my findings then. If there are no more issues I'll go with that if there are more issues I'll clear the codes again and unplug the MAF and test again. I just got done working a 14 hour day so I'm going to sit here with my TV and this beer and then maybe get another beer then bed.
:confused:

Okay good news the car is running as normal now not to say there weren't a few hardships along the way.

So as I stated before I reset codes. Only cylinder 5 came back as a misfire. So I tested the coil packs and the wires by swapping them. Side Note for n00bs like me. It's best to swap wires with the cylinder opposite the one you are working with on the block. The middle cylinders both have a longer wire where as the other 4 have a short and a long. So I went ahead and did the plugs on cylinder 5 hooked it all back up and wah lah. When I have more time this weekend I plan on replacing the remaining plugs. However cylinder 1 and 6 look like they are going be tough. I also accidently busted a plug wire in half pulling it out of the block so I had to go get a new one from the dealer. 50 bucks a wire at the dealer O_O. In any case thanks all for your help I just saved myself about 800 dollars. Thanks so much!

Oh man! but that is good news! - All plugs must be getting real old with all those other misfires recorded - Great - and now you know how to do it all yourself. If the plugs have not been done you should probably do a fuel filter sooner than later & make sure the car gets it's regular services. - Go well and let us know when you have finished - saved a bucket of boodle :y

On a side note, I recently had a CEL AFTER coming back from the dealership. They replaced the passenger side cats. They recommended that I get my MAF sensor replaced, spark plugs replaced, and the fuel filter replaced. MAF Sensor I think was around $636 and the plugs were $525. This past weekend I took out the MAF sensor and the throttle body to do some overdue cleaning to them. I took pictures and will be posting my experience on this job on the forum here with the pictures. I have a C320.

Thanks Pete - that would be great!

Multiple misfire on cylinder 1 and 3
 

Can any one give any ideas on how to fix this?First i have a bad MAF and stalls usually when my engine warms up and at stop signs when i try to take off.It drags for about 3secs and takes off.Now it's constantly vibrating and gave a multiple misfire on cylinders 1 and 3.I ordered the MAF.Any suggestions?

I would follow the same directions as stated above in this thread.

Thanks!:naughty: