no spark on #2,swap coils around still #2!

[Fillbilly]

Can anybody give me some guidance here? I can't figure out why I have no spark on #2. If it sits for a while it will run fine for about 2 miles, then it runs on 3 cylinders after that. It happened once so I replaced the coil with a cheap one and it fixed the problem. The same thing started happening again so I ordered 4 bav auto coils and noticed I had a loose plug wire.. oh well I put them on anyway.  Car ran great for a few hundred miles now it has a cylinder with no spark again. So I swapped coils around and still #2 is dead. Swapped wires, still #2. Any ideas I how to troubleshoot or resolve this would be a huge help.  Thanks

[Fillbilly]

Sorry, I forgot the details...it is a '91 318is

[1998ccc]

Have a know good DME to try?

Longshot.  Clean all grounds / connections and check #2 coil wiring.

Goodluck

[Fillbilly]

My buddy has an e36 with an m42, can I use an e36 dme in my e30?

[1998ccc]

Sorry, not sure.  e36 had knock sensors and EWS @ some point.

[DesktopDave]

You could probably use an early E36 DME to test. It's more or less the same part up until '92 IIRC when BMW added the DISA intake manifold, except with EWS on some models.

You might have a bad coil driver transistor inside the DME. I have a few DMEs with that problem, usually #2 or #3 goes bad. It's easy to find once you crack open the DME. I'll post some pics if I dig them up.

[Fillbilly]

So... I am still dealing with this problem. The car sat for a while as I was too busy to deal with it but I want it back on the road! I replaced all the grounds, battery and coils, plugs and plug wires. No change.
I got out the volt meter and found only 6-8volts on the "bad" coil plug. Tested for continuity from dme harness to coil plug-good, tested for resistance from theharness to coil plug-good(same as other 3 wires to dme) tested  voltage at dme (pin 52) and voltage is only 6-8 volts!? Other coil pins are normal 14ish. Oddly I tried another dme off the shelf from an e36 m42 (still a 175 dme) and the same thing. Is there a probable chance that they both have the same problem and I need to repair mine? Or is there something else to look at? This problem is Killin me! If I move the coils around the problem stays with pin 52 power so the coils should be fine as well.( Along with being new bav auto coils)

[DesktopDave]

Our DMEs occasionally develop problems with the coil drivers internally. Sometimes you can fix this problem by re-flowing the transistor leads with fresh solder. If the driver is damaged internally, it'll tend to stop firing once it warms up. You might have to replace one of the coil drivers if they're bad. I suspect that most of the M50 & M60 DMEs used the same Bosch transistor, but it's proprietary and out of production now.

[Fillbilly]

Thanks for that description Dave! It sounds spot on. You don't by chance have a schematic or a picture of which driver or transistor lead or for Coil #2 (pin 52 I believe) I have another 175 DME from an e36 M42 that I could salvage from I think. Maybe its not a surprise to those with experience, but both DME's I have are putting out low voltage on Pin 52. Not sure if that is a coincidence or if I am chasing the wrong gremlin.

[Fillbilly]

By the way, I am not exactly sure what I am looking for but, I did open up both DME's and nothing jumped out at me looking overheated or fried.

[DesktopDave]

If I can find the pic I took it definitely noticeable. They definitely look cooked if they overheated. Yours might still be good...did you re-flow the solder? Usually that'll fix low voltage issues.

[Fillbilly]

No, I have not tried to reflow the solder yet. I am not sure what to reflow. I will try to post a picture tomorrow when I'm home. Perhaps you could point it out to me so I can try it. That would be awesome if that fixed it.

[DesktopDave]

I couldn't find my pics, they probably got lost back when Photobucket broke the internet...

Just hit the driver transistor joints on the bottom of the board. There are four ignition drivers, all mounted under a clip-on heat sink on the right side. There are also two fuel injector drivers and a big voltage regulator on the left. Here's a good tutorial from Wayne at Pelican Parts:
https://www.pelicanparts.com/BMW/techarticles/E36-DME-Repair/E36-DME-Repair.htm

Just look for the bigger joints and flow a little more rosin-core solder into them with a low-wattage pencil-point iron. I've found it's best to tin the soldering iron first, since it's much easier to transfer heat with a tinned tip. Try not to put too much heat into the transistor leads, focus on melting the solder instead. It should only need a few seconds with a hot iron to fix a cold solder joint.

You shouldn't see many surface-mount components, but don't hit them with a hot iron...they're easy to break.

[Fillbilly]

Thanks for all the advice!  Here are some pictures of the 2 different dme's I have. The one with the square of tape is the original to the car (91) the one with the paint marker is from a 92 e36 m42. (With the same problem of low voltage on the same pin) does anybody see anything wrong or can you point out where I should reflow the solder for coil 2.
Thanks again!
The pictures are too large to upload so hopefully you'll be able to open the link. Let me know if you can't.

https://photos.app.goo.gl/xyMgUubMChUHyXPe8

[DesktopDave]

The coil drivers are under those metal spring clips, on the lower side of your first picture. I'm not sure if you'd already removed the clips, there's also a plastic spacer underneath. Once you've pulled them off, you can inspect the coil drivers for damage. A burned out transistor will be very noticeable, usually has a scorch mark in the center of the plastic casing. I pulled my spares out, took some pics & put up a blog post about it here.

The solder joints are marked on your board with D501, D502, D503, D504. They're each three separate leads. Just warm them up with a pencil-point iron and add enough solder for a nice little cone. No breaks, etc.. Wayne put up an excellent article about this at PelicanParts. Great pics too.