Author Topic: M42 misfire HELP (Read 3368 times)

Stringer · « **on:** May 27, 2012, 08:44:34 PM »

Hey guys,

I'm having some serious issues diagnosing a misfire with my 318is.

I've replaced/checked the following

DME
Plugs
Wires
Coil pack
Crank/cam sensor
coolant temp switch
AFM
TPS
FPR
Fuel pressure

The car used to be really bad until I replaced the plugs. Now it ONLY happens when it's warmed up to running temperature and under 2k RPM at WOT under heavy load (like 2nd gear/5th gear pulls). It is minor but still happens and is irritating me very much I feel like I've done everything.

Could it possibly be the wiring to the coolant temp switch? It only happening at running temperature is a major clue I just don't really know where to go from here.

Any help is much appreciated, thanks!

DesktopDave · « **Reply #1 on:** May 27, 2012, 10:43:50 PM »

Sounds like you've done everything I did. Might be a wiring issue, check what the DME thinks...did you do a stomp test?

Stringer · « **Reply #2 on:** May 28, 2012, 12:23:41 AM »

already did stomp test yields 1444... no code.

this issue is extremely frustrating because it only happens under those specific conditions so it's being a real pain to pinpoint.

DesktopDave · « **Reply #3 on:** May 28, 2012, 08:51:50 AM »

The temp sensors are pretty easy to test, it's on here somewhere...

The air temp sensor is pins 4&5 on the AFM connector.

I'd be tempted to pull the plugs again. You might see one that's different than the others. This is a far more useful technique for carbs, but it might help out with something like a weak coil/low compression/weak valve seals.

Once you're running warmed up & closed-loop the O2 sensor enters into the mix as well. Might just be getting lazy.

Stringer · « **Reply #4 on:** May 29, 2012, 08:15:49 PM »

checked 4&5 on the AFM and they weren't within spec so I swapped it out with another good AFM.

Misfire is still there.

Do I need to allow a few start ups for the DME to recognize the new part or what?

Stringer · « **Reply #5 on:** May 29, 2012, 10:27:05 PM »

also, i pulled off my throttle body the other day and there is a lot of what appears 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). not sure if this could be causing the miss.... anyone have any idea where it could be coming from?

Stringer · « **Reply #6 on:** June 03, 2012, 09:33:28 PM »

fixed it today! ended up being a crack in the intake boot and faulty wires.... ahhh that was so annoying! glad she's back on the road and running as she should be at last.

keflaman · « **Reply #7 on:** June 04, 2012, 06:36:54 AM »

What wires were faulty?