Another m42 misfire

[tehwickerman]

hey guys,

my engine has been quite a headache recently. it developed a misfire at WOT especially under 3k rpm and i have done the following trying to fix it.

coils
plugs
leads
cam/crank sensor
main relay
fuel pump
injectors
DME

pretty much everything you can do for a "simple" fix. i'm pretty stumped at this point but i don't want to give up and take it to a shop just yet. any help would be appreciated.

Thanks!

[cunninglinguist]

borrow an AFM, or clean yours.

[bmwm42]

Tps sensor

[tehwickerman]

already tried both of those too.

[VANOS714]

correct spark plugs and make sure theyre tight.

[vpilarrt]

Fpr?

[TobyB]

Check battery voltage (yup!) and fuel pressure at the rail. Plug wires again???

fwiw,

t

[vpilarrt]

Vacuum leak? Check the intake boot carefully (as in take it off and flex it all different ways while looking for cracks). All vacuum lines good?

[tehwickerman]

checked voltage, fuel pressure, FPR, everything good.

no vacuum leaks just did mess under the intake delete.

I put new plugs in it two days ago (NAPA didn't carry the twin electrode plugs so I just bought the best single electrode ones they have) and it cured the misfire completely.

However, i get in my car today and it's fucking back. this is starting to get extremely frustrating... what do you all think? if plugs solved it temporarily then could it possibly be the plug electrode spacing or something? I'm lost.

[tehwickerman]

It only happens after the engine is warmed up to its normal running temp.

I've replaced the coolant temp sensor but do you think it could possibly the be wiring to it?

[ISB E30]

Would you humor me and do a compression test? The HG may be slightly torn and car at temp could be pushing slight water vapor into the cylinder.

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[tehwickerman]

Compression is perfect got about 220 on all 4.

[ISB E30]

Also, pull back the rubber boot on your AFM plug and check the wire connections in there. I've seen them be really corroded and cause an issue like this.

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[tehwickerman]

done... everything looked normal.

this is making my brain hurt. i cannot think of any other possibilities.

[tehwickerman]

checked my AFM and found plugs 4 and 5 didn't ohm out correctly. put in one that worked well and the miss is still there.... i'm going to try replacing the o2 sensor and intake boot next. after that i'm out of ideas.

Also, I pulled off my intake mani and found a bunch of what appeared to be water vapor. it seems to be coming in through the pipe that goes from the valve cover to the throttle body (i've done mess under the intake delete). i'm not sure if this would have anything to do with this misfire but does anyone know where that could be coming from?