trying to pinpoint which coil is going bad in a 07 BMW 328i

[engatwork]

I've got the listed car in with an issue that it is missing at idle just every now and then. It is not frequent enough to set the check engine light. Using the Autel unit I am trying to determine which cylinder is missing by compairing adjacent cylinders "true running" reading. Seems that #4 spikes out at the exact same time it happens. Also, it seems that #5 cyl and #3 cyl spikes down at the same time. Can this be used as an indication that it is for sure the #4 cylinder that is missing?

[spdrun]

Is this a CoP ignition without wires? Check the plug ceramics for any hairline cracks -- had a devil of a time troubleshooting an intermittent miss in my (late, great) Miata, which turned out to be a tiny crack in a plug.

Other than that, do you have an extra coil that you could swap in one cyl at a time?

[Diesel911]

If there is more than one Coil in the Old Days there used to be a resistance reading you took with an Ohm Meter. For the resistance value you need to have an Manual or someone who knows what it is.

I am looking at the coils at at Internet Part seller. I don't know if what I said above would work or not.

Apparently there is some sort of resistance test; this is not for your Engine but mayge you can find the info you need on the Manual site:
BMW Workshop Manuals - 3 Series E36 316i (M43) COMP Workshop Manual - 4 RA Checking Ignition Coil (primary Coil) (M43, M44)

I think Pelican Parts has a BMW tech section.

[spdrun]

Originally Posted by Diesel911

If there is only One Coil for the whole Engine it dones not sound likely the Coil is the Problem.
If there is more than one Coil in the Old Dayse ther used to be a resistance reading you took with an Ohm Meter. For the resistance value you need to have an Manual or someone who knows what it is.

Do any 2000s cars still use a distributor, contact arm, and single coil? An ohmmeter won't tell all problems with a coil, because they frequently arc out when generating high voltage for the plugs. Unless your ohmmeter can push 30kV, it won't detect that kind of fault.

I've had good luck misting coils/wires with water to cause them to arc if there's an insulation problem.

[Angel]

Did you try the - "run the engine and use a spray bottle to mist the engine bay down, then look for sparks or misses" -trick ?

Only time I saw intermittent spark on my old VW, the coil was visibly cracked and got worse when damp or wet (and then you could see the spark jumping across the coil)

-John

[The Clk Man]

Originally Posted by engatwork

I've got the listed car in with an issue that it is missing at idle just every now and then. It is not frequent enough to set the check engine light. Using the Autel unit I am trying to determine which cylinder is missing by compairing adjacent cylinders "true running" reading. Seems that #4 spikes out at the exact same time it happens. Also, it seems that #5 cyl and #3 cyl spikes down at the same time. Can this be used as an indication that it is for sure the #4 cylinder that is missing?

DUH!!!! it's the one that doesn't work anymore.

[engatwork]

Thanks
I'll be trying another coil in #4 later in the week.

In the meantime as time allows I'll test em as the link describes.

[Pooka]

As weird as it sounds you might just try parking the car somewhere where it is dark, lifting the hood, and looking for the electrical glow.

I have done this with older cars. You can actually see the pulses of voltage running down the ignition wires if they are worn out enough.

It has to be really dark, but at night you can just lift the hood and turn off the flashlight. The worst that can happen is nothing.

[p7fan]

Is that a Maxi Das your using to check the "cool runnings" mon? Your on the right path. Late model Bimmers will puke a coil in a second.....

[kmaysob]

what about pulling the plugs? if its pretty consistently missing, you should find an overly rich plug.

edit, i reread and see its only every once in a while

[engatwork]

It is a MaxiDas unit. I've watched all six cylinders (graphing two at a time) and the only cyl that spikes high when it happens is #4.

[p7fan]

The maxi das is a pretty cool unit. We have that, a launch, and a genesis (ugh) at work. Typically the launch is my go to on the BMW. One of these days I plan to play around with the misfire graphing on the maxi, but I haven't yet. Typically when I hook up to the bimmer's they have stored a cylinder specific misfire code.

For kicks you could swap the coil to another cylinder just to see how the graphing responds. Its possible its a plug, or a plug/coil saturated with oil.....

You've got it under control.............

John

[barry12345]

I wonder if clear tape where used to affix a neon bulb to the spark plug wire surface might show the miss. Very old technology but usually they pick up eough energy to glow until the excitation is gone.

You know the type as simular to those in some electrical testers. Used to be fifty cents a bulb. They could even be liberated out of old appliances at one time.

[engatwork]

or a plug/coil saturated with oil.....

#4 had oil down around the plug/connector. Time for a new valve cover gasket. I did not bother looking at the others but have scheduled to do it when it gets new plugs here in about 15k miles unless it gets alot worse.