C32 AMG Cylinder 5 misfire help

[C32Steve]

Hi all,
My C32 is currently misfiring on cylinder 5. I have no real mechanical know how so it went straight to an indie Merc specialist in Norfolk I've used regularly shortly before Christmas when this started. Through their testing and replacing of things they've discounted, plugs, lead, coilpacks, fuel injector and ECU (after that was suspected and sent for testing but came back fine).

Its now had compression test and is is showing as low on cylinder 5. More specifically, when cold it initially doesn't misfire but I'm told the compression drops significantly when hot and the misfire starts.

I'm hoping to get an confirmation of the fault codes that Star showed when it was last tested on Monday to post for further detail.
I'm told the suspicion now is there could be damage to the piston or piston rings and potentially cylinder bore so I'm asking for some further investigation to clarify further.

There does seem to be a lot of threads from other owners and independents who've worked on C32's with misfires so despite knowing fairly little about the terms I've read plenty around Camlobe separation on 2002 models, water in fuel rails, broken value springs, bad cats and leaking IC pumps (which was the cause of a previous misfire it had about 3 years ago) but I haven't heard anything back to suggest one of these is the culprit.

Initially this misfire started a couple of times during very heavy rain whilst driving on roads with a lot of standing water, it happened twice where it started during these conditions and then would stop as soon once the rain eased off. A month or so later on a normal drive it became permanent.

Having started this post I'm not really sure if I've got a structured question but just wonder if anyone has any thoughts on next investigation steps or advice?

There is currently a reconditioned C32 engine for sale on ebay but given investigation costs are already mounting I feel I need to weigh up likely total costs of repair against the cars value. It would just feel such a shame to sell it as a non-runner given my attachment to it and that it's otherwise in well serviced good condition.

 

[Uncle Benz]

If the cylinder compression is significantly low, that is where the problem lies. A borescope may elicit further evidence without opening the engine. The number of misfires allowed before cylinder cut is active, is adjustable with Star, but if the compression is very low, this step may not get you anywhere.

("anywhere" being a position where it may be possible to escape from ownership without considerable financial loss, as if I'd suggest such a thing...)

 

[C32Steve]

Spoke to the garage again tonight.

The Fault codes are

P2049 Misfiring of cylinder five (P0305)
P2043 Misfiring (P0300)
P2056 Misfiring of cylinder five, damages three way catalyst (P0305)

Current choices being presented are a) sourcing and fitting a replacement engine, quoted approx £3k labour + engine cost or b) selling as non-runner to a Mercedes breaker.

Given list of things previously discounted in from first post can anyone thing of any other suggestions?

Given value of car seems to be around 5k max the replacement engine choice doesn't really feel viable. Would others draw a line under it and move on or continue repair investigations?

 

[V6Matty]

Doesn't sound good Steve but if the rest of the car is good and you could afford the replacement then keep the car the 32 is such a lovely thing it would be a shame to see it go to a breaker.

 

[Uncle Benz]

Whereabouts are you located??

 

[C32Steve]

Yes its a tough call, financially I think its going to make sense to move on and for my circumstances I really need a more reliable daily driver. But, its a C32 and for all its sins its hard falling out of love with it!

I'm based in Norfolk!

 

[Uncle Benz]

May I suggest you let Alex Crow take a look at it?

 

[C32Steve]

Thanks UB I've spoken to Alex briefly this morning and agreed to share all the details I've got over email to see what his opinion is.

 

[Steve@Avantgarde]

From my point of view, Ive never had to open up a 112 based AMG engine, they are quite bullet proof. I have never seen one hole a piston, wear cam shafts or any other degree of engine wear, thats not to say there hasnt been, its just incredibly rare.

Misfires on cylinders on these engines can be down to water or condensation in the fuel rail. This is relatively easy to sort out but you usally get a misfire on cylinder 4 where the rail sits lower on that bank than bank 1, and cylinder 5 can also trigger. So possibly something to visit.

If a compression test has been done and is found to be low then that is usually confirmation that there has been a failure of some description on that cylinder. I would like to think if its worn a cam lobe or dropped a valve it would rattle, tap or knock. Have you experienced this?

What I have seen twice, not on an AMG engine but on 240 and 320 petrol engines is catalyst break up. I believe there was a technical bulettin relased by MB some years ago (circa 2004-05) which related to a broken catalyst sucking swarf back up into the engine and hence destroying bores and piston rings etc. When I was manager of MB Bath I had to deal with 2 cases of this and remember thinking what a bizzare fault to occur. So this could be another avenue to look at.

Either way if you have it confirmed that the compression is low on that cylinder, it might pay to whip the head off. I imagine it would take about 4-6 hours.

I have to say, the cost of £3k Labour sounds incredibly steep to swap an engine. It would take about 2.5 days which I estimate would be about £1500 +VAT.

My advice would definately have Alex Crow look at it if you are in his neck of the woods. One of the most knowledagable techs you will ever likely to meet and will no doubt give you the absolute correct and best advice.

Best of luck with it and please post your future findings, I would find it of interest.

 

[C32Steve]

Thanks Steve, I'm going to drop Alex a note with the details and will see what the best course of action is following that and share.

From my searching the only guys I've found who've had major C32 engine issues in the past were on the US forum and had made performance mods (mine is stock) - like in this thread -

http://mbworld.org/forums/c32-amg-c55-amg-w203/391757-destroyed-c32-engines.html

 

[Alex Crow]

My thoughts so far, as above.

With blocked cats we expect missfire on eg 1,2 and 3 or 4,5 and 6.
Water in fuel rail would not normally be just no.5 missing.
Low compression, if confirmed, would lead to a cylinder leakage test, to see if top or bottom end losing pressure.
A worn cam lobe would have to be really bad to give low values during a compression test.
Ingested cat debris is possible, but I have never heard of this on the AMG M112.

What do we usually find? Failing HT leads, spark plugs or ignition coil, although I read that these have all been ruled out, and compression is low = cylinder leakage test as next step.