Help! Any S52 gurus? M3 Evo injection problem

[Tahiti450]

Hi, my first post on the BMW forum, I'm an imposter from the TVR side please indulge me!

RE: my wifes 1998 E36 M3 Evo cab (c 70000 miles) FBMWSH etc.

Started running roughly at idle breifly after starting (and requiring more cranking to start) over last 6-8 months but otehrwsie running fine seemingly. Recently I went to move the car after shed been on a long run and noticed a persistent regular misfire and fuel fumes from exhaust. Started investigating this at home -
Findings:

No 6 plug wet with fuel and cylinder filling with large amounts of fuel.
No sign of any piston bore or valve damage on inspection with endoscope.
Compressions all ok,
Swapped plugs, no change, still No6
Injector removed and seems to seal fine with compressed air and opening with 12v feed, but replaced injector anyway - no change.
Coil packs swapped but still not firing on No6.
Checked coil secondary traces with oscilloscope, all appear ok
Checked injector signals with oscilloscope, again all ok and same as other cylinders.
Throttles all opening normally and linkage checked.

Note: when throttle opened sharply the misfire stops and if the ignition is switched off during the acceleration phase the No 6 plug is dry but sooty suggesting that the xs fuel is being burnt but the cylinder is still grossly rich.

At this point I took the car to the BMW agent thinking ECU problem or similar.

They confirm:
Fuel presure normal.
Coils normal,
No fault codes (well only oil level sensor, which has been on the blink)
Bank 2 lambda correction outside control range.
Changed plugs with no benefit.

They were then going to check the cams, valve clearances etc, so i had the car back to do this myself. So not really any the wiser after parting with £400!

Today, cam cover off:
Cams - no evidence of wear or damage.
Clearances adequate tho i am not sure of the actual spec (measured at 8-10 thou - 0.2 - 0.25mm)
Compressions ok
Cam timimg appears fine on eyeballing - with No1 piston at TDC between exhaust and induction stroke (overlap phase) cams are symetrical with exhaust valves near closed and inlets just opening.

So after all this I know what its not but it basically seems to be overfuelling on No 6 with no obvious explanation.

Any suggestions please!!

many thanks
Alan

[dan101smith]

I'm sorry I can't advise on this one, but might be worth also posting over on www.bmwowner.com.

[Cactussed]

Have you changed the HT leads?
Could be a hairline crack in number 6 lead core, leading to intermittent misfire.
Almost impossible to trace as it isnt constant.

If no joy, move back along the line and start on the distributor?

[Tahiti450]

Cactussed said:

Have you changed the HT leads?
Could be a hairline crack in number 6 lead core, leading to intermittent misfire.
Almost impossible to trace as it isnt constant.

If no joy, move back along the line and start on the distributor?

Hi thanks,

There are no HT leads (coil per cylinder) and the coils all check out ok and have been swapped over but same cylinder affected. There is no distributor as the M3 has mapped ignition driven directly from the ECU via signals from the crank / cam triggers and knock sensors.

Cheers
Alan.

[Cactussed]

Ah. Hmmm.

Replaced injector so rules that out.
Replaced coils so rules that out.
Replaced plugs so rules that out. Assuming gaps are Ok.
Timing and clearances are checked and OK.

Presume you have swapped between cylinders with items above that you know definitely work (as small but distinct posibility of a bad replacement item.

That only really leaves faulty signal going to the coil pack? Dodgy wire to #6 or faulty ECU? Revving the car could be causing sufficient movement in the engine for a poor wire to intermittently send signal?

[Boulder]

Might possibly be an exhaust valve sticking,once saw it on a 318i.

[Tahiti450]

Boulder said:

Might possibly be an exhaust valve sticking,once saw it on a 318i.

Good point - but compression test normal so not a valve problem.