qjumpr

Hi,

New code P0401, see below for updates and progress.


I've had the P0304 code come up on my CLK63 BS (Misfire Cylinder 4). The car itself drove home just fine as I noticed the CEL about 5 miles from my house.

Once home the idle was horrible, so I shut it down, ran the code, tried to restart to see how bad it was and run some diagnostics, but it wouldn't fire up.

I've done a bunch of searching and am going to start with the Plugs, wires, coils etc and look at all them, but after GIS and searching on here I'm lost trying to find a diagram of the cylinder layout for the M156 engine. Anyone have one?

Also any advice, or thoughts on other issues?

Car has 74k miles
Plugs changed at 65k miles
MAF's cleaned at 65k miles
New in tank fuel filter at 65k miles
New OEM air filters at 65k miles
New PCV at 65k miles
Very strong smell of fuel once I tried to restart it

I'll post up once I have looked over everything I can see in the morning.

Thanks!

rentzington

I think that's the code I got when my belt slipped and cut the wiring loom which threw tons of codes on the passenger side banks.
Might be worth checking for any slipped belts or sheared wires

mb techman

hmmm.... im hoping this isnt the problem, but i encountered this on an E63 not too long ago.

They injector on cylinder #8 ending up sticking open, causing the cylinder to flood with fuel and bend the rod. The cylinder #4 spark plug will be much cleaner than the others, since the fuel will have "washed" the spark plug.

Thats your worst case scenario. A much better but still not great scenario is a broken headbolt around the cylinder #3, cylinder #4 area.

A compression test or cylinder leak down test will give you more answers.

But as a tech with limited info, thats what I would be leaning towards.

qjumpr

^^ thanks for the info, any way I can do compression test at home?

I was always told that the BS engines were not effected by the head bolt issue??

Merc63

Pull the plugs and number them, check them and see how it's running. Could need new primary o2 sensors.

qjumpr

I will do that first thing in the morning, however wouldn't it show a misfire on more than one cylinder on that bank though if the O2 sensor was out??

qjumpr

Update:

I've pulled the plugs and the number 4 cylinder has fuel on the plug (all the others look good). So I'm guessing next on the list is swapping coils to see if that is bad. Then if needed pulling the fuel injector?

Merc63

Yep both have known to be a problem at some point.

qjumpr

Update 2:

I cleaned off the plug, swapped the coil with the number 3 cylinder, cleared the code and decided to see if she would start.

It was a little hard to fire, but once it did, she started up, idled rough, blew some white condensation smoke out the exhaust (its 40 degrees here today) and that was it.

After a couple of minutes, I turned it off then restarted it. On the second start it fired up like nothing was wrong, idled 95% perfect, so I took it for a short 1 mile drive through my neighborhood and it ran great. The white smoke stopped once it was up to temp.

Once parked in the garage I ran any pending codes as the CEL was not on, and P0401 came up as pending, no other codes.

So thats were I'm at. A visual inspection of the gaskets/injector seals etc all seem good.

As a result I'm out of ideas, something is obviously not right, and I figure P0401 will set off the CEL soon so any new ideas??

Thanks for all the advice so far!

akmatic63

having a weird similar issue. CEL, hooked it up to SDS the codes were cylinder 6 misfire and upstream O2 error. Not sure what is causing what to go, I'm thinking I probably filled up bad gas. I topped up gas and currently working on finishing the tank.

Its weird sometimes the car will run like nothing is wrong, when i had the car hooked up the O2 code was stored and all the values were perfectly normal. Cleared the code, then the misfire started again. then the misfire went away completely, cel still on, car is driving normal. real strange I have yet to pull plugs and do a physical examination.

Merc63

Gjumpr, that code is for the egr.

Almatic, the o2 sensor if it's not reading right could cause mixture
Problems. Headers usually cause the o2 sensors to fail after install for some reason.

qjumpr

Yeah, I figured that would need to be cleaned, everything I've read online says the valve itself is rarely at fault, but I'll clean everything out and see if that helps.

I also scrape my exhaust on that side every time I come in and out of my garage and there is no way around it, I've tried, including raising the exhaust. I figure something might have pulled loose from the headers as well.