GA25331 has had a history of rough running since Taffy bought the M5 and here's what we've been through so far
1. Found intake temp sensor not connected, action : reconnected
2. Found K+N filter and lots of grit and GRAVEL in the intake box, action : replaced with a new OEM air filter
3. Dirty MAF , action : cleaned MAF and then replaced with a new MAF
4. Found sulphur like yellow deposits on plugs action : replaced plugs with new plugs
5. Valve shim clearances done generally shim clearances were good and we changed out 6 shims (compared to 17 on my engine)
6. ITBs balanced , these were out on 2 cyls
7. Checked compression, readings 1 to 6 were 180, 180, 180, 180, 180, 190 (an aircraft mechanic friend said these readings are WAY TOO CONSISTENT and suspected each of the cylinders had oil in them, we didn't do a dry and wet compression test at the time)
8. Replaced injectors with new injectors
Each change made good improvements (the big ones were the MAF , valve shims and injectors) and the engine runs smoothly and doesn't hunt at idle anymore but GA25331 has started to consume 1 litre of oil for 200kms so somethings not right.
A future M5 owner has joined our group (Glenn 21 yrs old and keen as hell) who has just completed his automotive engineering course in Australia and builds Nissans and other cars (Nissan GTR and other rice racers) for drifting
Glenn's further investigations found (and I'm reporting this remotely, Glenn will update later)
1. The cam cover wasn't square , 0.2mm from true
2. The head gasket showed some 'erosion'
3. Then looking further into the head gasket Glenn removed the head found that the cyl head studs around cyls 1, 5 and 6 (also the ones with the bad injectors we replaced) had lost tension due to thread damage
4. Valve guides worn
5. Reports that the oil pump drive sprocket is damaged / stripped (engine backfire at high speed ?) , waiting for photos, I can't picture in my mind what's happened here.
Speaking to my aircraft mechanic friend (who also used to build drag car engines) when he looked at a photo of the piston crown it appeared to him that cyls 1, 5 and 6 were running hot and the engine has detonated , backfired or done something nasty during a hard pull then sudden back off on the throttle. It's also possible GA25331 got a load of contaminated fuel (lower octane than advertised or cut with other chemicals)
We've decided to tap into the M5board and see what the M5 wizards (in blue coats) can come up with.
Taffy's decided to pull the engine and get Glenn to go right over it.
This all happened since a 220kmh run which Taffy did on his own a few months ago.
Other than high oil consumption the engine runs and idles smoothly and produces good power.
I'm doing this third person , the M5 is 150kms away at the moment.