Misfires # cyl 1

[JoepM5]

Hi all,

My M5 is in the shop for a misfire problem on cylinder #1.

Recently the car started misfiring, most noticeably in higher gears (4/5) under moderate load. However, also when idiling a misfire was noticeable every 20-30 sec or so.

The shop has already swapped coil packs and spark plugs (both are new anyway) and that didn't solve it. Next thing they are thinking about is the injector. However, car got new injectors (as well as high pressure fuel pumps) last year (< 15k kms ago).

Any suggestions here what can cause this issue? Car is a 2012 model and fully stock. Mileage around 200k kms.

Any input is greatly appreciated.

Best,
Joep

[M5Rick]

At 200k I'd have a compression test if not done already.

[JoepM5]

Hi,

Thanks for the input.

Compression test was also done 15k kms and 10k kms ago, no weird things showed up back then.

Best,
Joep

[M5Rick]

The only other thing I can suggest is an engine carbon cleanout, try Gumout which is claimed to remove light carbon deposits but it may need a dozen applications or so though it may not work on heavy ingrained deposits...if it is that, then the only answer is to remove the c/heads for inspection, cleaning and polishing of heads and possibly regrind valve facings.
Had a mate regrind the valves and polish the heads and pot tops in a classic TR5 PI that I used to own and it transformed the engine into a non-misfiring smooth rocket, it was straightforward removing the 6 pot head after the rocker cover was removed with the simple OHV design.
An M5 owner, I think it was Strip DJ had a top end rebuild on his M5 and the amount of s*it around the exhaust ports has to be seen in the pics, you'll have to look for it about 2 years back now.

[TinCanSailor]

If you can install a water/methanol injection system it too can help clean the intake valves. The oil that enters the intake system via the pcv is absurd.

I am considering adding a vent to air catch can setup on my new engine after it goes in. The oil burns and builds up on the intake and the oil / oil fumes reduce octane.

[JoepM5]

FYI - it turned out to be a faulty injector anyhow, although only ~15 months and ~15k kms old...bad luck I guess but happy its fixed

[TinCanSailor]

I have read where others have had new injectors and/or coils were bad right out of the box. Appreciate the follow up.