Isolating a miss

[upallnight]

How can you tell which cylinder is missing if you have coil packs? In the past I would just pull a spark plug wire off the plug to see if that cylinder is firing, but with coil packs how can you perform this test to determine which cylinder is causing the miss?

[mtg729]

Spark plug test tool.

[muckRunner]

a free way is to pull each plug wire one at a time (carefully, you stand a good chance of turning your car into a tazer, lol)

the good ones will cause the engine to drop rpms or bog, the one thats missing will have a slight or no change in idle and how it runs.

[Mr Project]

Or you can unplug the coil connectors one by one. The signal from the ECU is a 0-5v signal, so it's low voltage. Did this on my M60B30 when trying to chase down a miss.

[upallnight]

Or you can unplug the coil connectors one by one. The signal from the ECU is a 0-5v signal, so it's low voltage. Did this on my M30B30 when trying to chase down a miss.

Can you unplug the connector with the engine running? I'm going to use an infared thermometer and see if their is any difference in the exhaust manifold runner temperature. I'm hoping that the missing cylinder will have a cooler temperature compare with the good cylinder. Thanks for the insight.

[dansgt]

its alot easier and safer with coil over plugs, you're not unplugging the spark, your unplugging the signal. same concept cept you wont get the spark through you if you're not carefull lol. but if you're unsure you can swap packs, if the miss moves with the pack, you've got a bad coil pack.

[M Quick]

Or you can unplug the coil connectors one by one. The signal from the ECU is a 0-5v signal, so it's low voltage. Did this on my M30B30 when trying to chase down a miss.


M30B30 with coil packs? Hmm, is that something you have self made at home?
Just curious. But i might think that you meant m60b30, but if you didn't how did you convert it to coil packs on an m30?

[Mr Project]

Oops, sorry, I meant M60B30, sorry for the typo. Yeah, a euro M30B30 would not have had coil-on-plug.

I did pull them with the engine running, though it would be better to move the coil packs around as dansgt mentions, I was lazy and having trouble narrowing it down, so I pulled the connectors one at a time while running.

In my case I found that the coil drivers in the DME were bad, so don't discount that as a possibility. If you find the bad cylinders I'd check the DME output before spending $40-50 a pop on coils.

[paanta]

Stethoscope. One of the ones with a long, pointy metal tip sold at any decent auto parts store.

[Mr Project]

Check out my M60 misfire thread here for more info:

http://forums.bimmerforums.com/forum/showthread.php?t=1189254&highlight=DME

[upallnight]

Check out my M60 misfire thread here for more info:

http://forums.bimmerforums.com/forum/showthread.php?t=1189254&highlight=DME


Thanks for the info. This engine miss did start after I changed the DME. My other DME has a Turner Motorsport Chip in it and I wanted to use a stock chip for the winter season. The Turner chip did have a slight miss that went away as the engine got hot, but with the stock chip the miss remained even after the engine got hot.

Well, I was able to identify the miss firing cylinder. Started the engine and let it warm for a minute to get the exhaust runners hot. Took out the infared thermometer and took a shot at all the runners. All the cylinder were at 170 degree F whereas cylinder no.5 only showed 70 degree F.

Will replace the DME and see if that might be the cause of the problems.

[muckRunner]

wow, infrared i have to admit is the best way. my old (not old, i just dont have it anymore) truck had a distributor, didnt even think about pulling the signal wired to the packs.

[upallnight]

The touring is running good again. Switch back to my old DME. Replace a coil pack and spark plug. Switching back to the old DME got rid of most of the miss problems, but there was still a miss. Used the infared thermometer to identify the cylinder that was missing. Replace the spark plug with a new plug that I brought at Pep Girl on "Black Friday" and replace the coil pack with a spare that I had lying around. Started the engine and check the exhaust runner temp with the infared thermometer. All cylinders were pretty close in term of temp reading. Miss is gone and I don't miss it. LOL

[dansgt]

I did pull them with the engine running, though it would be better to move the coil packs around as dansgt mentions, I was lazy and having trouble narrowing it down, so I pulled the connectors one at a time while running.

In my case I found that the coil drivers in the DME were bad, so don't discount that as a possibility. If you find the bad cylinders I'd check the DME output before spending $40-50 a pop on coils.
thats why i recommend moving them around, you almost instantly rule out the possibility of it being a bad pack or if its something else. i like how you used the infared thermometer to find where the miss was, thats a great trick, those things are so useful with diagnostics.