666baddy

I have the engine check light on.
I am told it is a missfire on 4 & 8.
If I accelerate hard then the car missfires (almost stalling). If I switch the car off and back on again then it seems to reset until I accelerate hard again.

I have changed plugs, leads, coil packs & injectors and it hasn't changed.
I have also changed the MAF sensor and still no good.

Can anyone else help.

Many thanks

bkjr

Did replace both of the plug wires on 4 & 8.
I have seen this before and replacing the wires took care of that.

666baddy

I have replaced both spark plug leads on 4 & 8. (4 leads in total).

Moviela

There may be a bad engine wiring harness. I have not heard of this on a ML, but if the primary leads to the coil packs have hard, brittle, and/or cracking insulation, that might be the source of your misfire.

When you took out the old plug, were the deposits a nice toasty brown? That is a well working plug. If it was black, that might be fouling the plug causing the misfire. Sometimes this is caused by poor quality petrol (gasoline for the yanks.) This can be fixed by using a fuel system cleaner in the petrol tank. Look for a product with tolulene.

MBTech21

2 things to check for this issue-

First, has the sensor gear adaptation been reset? It needs to be, especially on the MLs after fixing a misfire.
Second, if #1 cylinder is actually misfiring, then the computer gets confused and starts flagging other cylinders- seen this on a couple MLs.

Hope this helps

BeNzTeK

Exactly MBTECH
self adaptation wit the mass air flow sensor I have found out that manually setting this sensor doents always work resetting it through DAS does

BenzForeman510

You might also want to check your O2 sensors...seen this cause it also...

TECHNICIAN

Fuel filter.

Pull off the black rubber hose. If fuel leaks out, or its wet at all, I'd bet money thats your problem.

Driver55er

Did you recently disconnect or drain your battery? My car ran perfectly until that happened and now I am having the same issue with my 4 and 7 cylinders. We tried replacing coils, wires, plugs and injectors but still no luck. My car runs fine until you take it over 4k rpm and then it misfires really badly. If you shut it down and restart it the car is fine. Let me know what you find out.

PS How do you manually reset the DAS?

Lordy76

Did you ever manage to sort out the misfire problem. I have a 2001 ML55 and have misfires in 4 out of 8 cylinders!! I was advised plugs/leads etc etc but before i do this the Merc dealer advised it might be water in the fuel range/gauge??!!

Did you ever sort the problem out.

Lordy

fizzle

techs...how do you reset the sensor gear adapation?? disconnect the battery for awhile?

Lordy76

Still got the misfires. General misfire and on cylinder 2 and 6. Ive changed plugs, leads and 3 coils and still have the huge misfire!!! Has anyone got any ideas? Its getting very expensive now.

Lordy

SMARTSSUCK

have you checked if the misfires are coming from the same cylinders that were missing before?

Lordy76

It seems to be just the same cylinders again and agin this time. I clear them then its 2 and 6 everytime withe the general misfire code too.

Prior to plugs, leads and Airflow meter it was ramdom....was misfiring on upto 4/5 of 8 cylinders.

Have tried using fuel cleaner over the weekend and using super unleaded as i it was suggested that the supermarket fuel i was using might not be helping.

The car is very jerky especially on the motorway at 80ish. It eventually gets to the stage that black smoke come out the exhaust until the cylinders all kick in then it goes.

Really stuck with this one!!!!!

LukeM

Run top tier gas always if possible.

http://www.toptiergas.com/retailers.html

Professor21

Did anyone ever figure this one out? I'm having the same issue with my 2001 ML55

THANKS...

Professor21

Got it fixed. Turned out to be the Catalytic Converters. Left front fell apart and the baffle went into the rear. Caused the rear to be backed up (plugged up) and created the misfire error. Not sure this will be the fix every time but before you replace your plugs/wires or start changing fuel components, take a few minutes and check the cats... Could save you a lot of time.

cortschrothNJ

I would just do a straight base diag first to make sure you have air/fuel/spark/compression, if those all check out which they most likely will, id say then monitor some pid data while its happening, check your fuel trims, o2, ckp,cmp,maf, and any others you'd want to look at and try to find some abnormality. If you havent checked the fuel filter lately id do a pump volume test at the rail. If you recently unplugged anything such as the throttle body or any other electronic motors they may need adaptation. Id also check for any leaks in the intake system. Were there any other codes present relating to the engine?(rich/lean banks, signal/circuit codes, communication, ect.) check engine steady on or flashing?

cortschrothNJ

AHH just saw the cat post, yes that too, misfires suck

Professor21

Just need to make sure to do the other side soon.