I have a 91 325i with a m42 swapped in it. It has a cop conversion. This weekend I replaced the valve cover gasket. One of the studs would not make torque spec but it was only one and all the others torqued to spec. I waited a day before I tried to start it and it started to miss on #4 while I was warming it up in the garage. I held my and and ear by the suspect stud but didn't notice and vaccum , all of a sudden the #4 coil pack puked black goop out of the side and started to smoke like crazy. I thought it was just a bad coil pack so I found two extra at the local yard. I got home and tried swapping them around and managed to melt two more coil packs. I tried splicing in a different coil plug on number 4 and no change. I even tried swapping in a extra ecu and no change. The car has new plugs with the gasket change so I tried and old plug in #4 and still nothing. I know it's not firing because there is fuel on the plug. The coil is getting super hot so it has to be getting power right? I have no clue what to try next at this point please help!
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One of the melted coil packsAttached Files -
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Do the fried coils follow connector #4, or are they always on cylinder #4 regardless of which connector (1, 2 or 3) is hooked up? How quickly did the replacements fry after swapping them in?
Coils barf like that when the primary circuit is shorted. Get a multimeter and check the continuity between pin 1 (connector side, not the coil) and a ground point. The wire for pin 1 is black (pin 3 wire is green and show 12V when the key is in run mode, pin 2 wire is brown/orange and connected to ground). Pin 1 should be high impedance / no continuity to ground. If it is showing continuity to ground, then your harness is damaged/pinched somewhere. The wire for pin 1 has a shield around it, which is grounded, so it is also possible that the short is due to the wire being pinched and touching the shield, rather than a chassis ground. This is dangerous because the shield is not rated to deal with that sort of current.Comment
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Great info! I was thinking of unwrapping the harness and inspecting pinch points, does that sound like a start? Yes I tried swapping connectors and no change I could not tell if it was still #4 not firing, the car isn't throwing codes. What shield are you speaking of? Electrical is not one of my strengths
Not to get too much on a tangent, but recently after an autox I started getting this doing coming from the dash similar to the servo noise you get when you use your hvac controls. The noise is coninuose and sounds like a CD player changing discs over and over again. I know it's hvac related because I pulled the fuse and it stopped. I'm hoping this has not caused a short deep under the dash somewhereComment
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There is an electrically conductive shield around the black wire for pin 1 of the ignition coil connectors. This is to reduce electromagnetic interference emitted by this wire because it carries a large current for brief periods and...anyway, there is a powered wire surrounded by insulation, then a big bunch of copper wrapped around that which is grounded (the shield).
As for the dash noise, I can't really help you there. It might be the air recirculation flap/motor, but I am not sure. You might have to pull the dash, or at least the HVAC panel, to troubleshoot this.Comment
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Ohh, yeah I noticed that when I soldered a new wire... It was broken in one spot where the inner wire was mixing with th outter shield... But I trimmed back the shield when I soldiered on a new wire from an obdII car and now the last 3in has no shield. Did I fix the problem with another problem? Damn probably going to miss autox this weekend.Comment
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I know the wire you are talking about but what do you mean by "pin 1,connector side"? Do you mean the diagnostic port on the other side of the egine bay?Originally posted by bmwman91 View Post
Since i now see that the wires that plug into the coils are part of the main harness with no connectors on the other side, did I just screw my self by soldering a new plug on since the shielding is no covering the last few inches ? How can I fix this? If I locate a pinch with the multimeter how can I repair if I can't solder the shielded black wire?Attached FilesComment
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"Pin 1, connector side" just means pin/terminal 1 in side the 3-position plug that connects to the coil pack. There is the coil side, and the connector side.
I am not entirely following what all you did since it sounds like a bunch of splicing was performed. Anyway, it sounds like you know what to start looking for now that you know about the shield. In the OEM setup, the shield is trimmed back maybe 1cm from the end where it goes into the plastic connector inside the rubber boot. Trimming it back too far is not the reason for the melted coils though. While it is certainly not ideal, if you are only missing a few inches of shielding, you are probably OK (you might just get a little extra noise when listening to the radio).
If I had to guess, there is probably some sort of issue with the shield shorting out on one of your splices. Was the car running fine up until you removed/reinstalled the valve cover? If so, then chances are something either got pinched, or maybe the soldering job wasn't done super well and bending the wires caused a new short in the splices. Get a couple of well lit close-up/macro pics of the splices you did, and maybe consider trimming off the shrink tubing for a better inspection. You can always re-solder the connections and put on new tubing.Comment
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As a test I tried splicing in a new plug for #4 since I noticed the last cm of the shield was frayed before the plug, it has a softer covering material last cm before the plug. Other than splicing a new plug that's all that was done. Yes it ran fine before the vc job. I'll try to take apart my splices to make sure no shield it touching the inner wire and splice. Any other ideas? I'm wondering if a short occurred within the dash since I have that hvac solenoid sound tuning constant?Comment
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Hmm, yeah get in there and get get a good look at the engine harness. Does the noise change with RPM? This could be the high current connection arcing to a ground short, which is definitely a fire hazard.Comment
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No it sounds the same from idle, #4 not firing plug is wet with fuelOriginally posted by bmwman91 View PostComment
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I re soldered the power wire making sure to trim the shield to avoid interference. She running well. Thanks for the help man!!!!Comment
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Nope. What if I just pull the green 30amp fuse will I harm anything besides sweat from no ac?Comment
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