New Engine Suddenly Running on 3 Cylinders

[bmwman91]

OK, so just after I fixed my lousy idle on my new motor (big vacuum leak), the car decides to run on 3 cylinders. I managed to limp home with it sounding like a Harley motorcycle to take a look at things. Prior to that, it was running great and I got a good ~80 miles on it.

Spark plug #2 was covered in carbon and wet with fuel. Plugging/unplugging the coil pack didn't seem to make much difference, whereas unplugging any of the other 3 seemed to cause a stall (with throttle held open, can't idle otherwise). Just to be sure, I swapped coils 2 & 3, and it seemed like it followed the coil, sort of. Anyway, I ran all over town and found a replacement coil (I am using a COP conversion) and replaced the suspected bad one. No improvement. I swapped spark plug #2 with a known good one from my old motor. No improvement.

So, I sort of have no idea what it could be. It seemed to be an obvious spark issue since the plug was fouled and wet with fuel. That rules out a plugged injector I think. How about a stuck one? MM provided cleaned/rebuilt ones, so it seems unlikely. The failure seemed to follow one coil, although it was running so poorly that it was hard to tell, and a new one didn't help. Maybe a wire broke in the connector or something, or maybe the DME coil driver died. I am going to try picking up a spare DME and ignition parts from a local member tomorrow morning to swap that stuff on and see if it helps.

Any other ideas? This is really really getting old. At this point, I think that I need a boring, reliable daily driver of some sort, either in addition to, or as a replacement for this car. I have sunk far too much time and money into it, and I am tired of screwing with it only to have it frequently fail me at random times.

[AndrewBird]

Pull the ECU out and take a look at the transistors that fire the coils. They are known to fry. I had one smoke on me.

[bmwman91]

Interesting. When it went, did the car run at all? I forgot to mention that after [whatever] broke, the exhaust got very LOUD. Did this happen to you too? I need to do a compression test to see if a valve crapped out (unlikely since the motor is new and professionally assembled). I am not sure if a non-firing cylinder would cause excessive exhaust noise by sending a full air/fuel charge down that way.

In the years before the driver went, did you find that ignition coils were failing frequently (every couple of years)?

It looks like you added some thermal gap pads between the ICs and the heat sinks. Or is that a stock thermal pad?

[bmwman91]

Well, I found the problem. For now I am going to keep the details to myself since I have a lot of phone calls to make over the next couple of days. Thanks for the help!

[AndrewBird]

I bought the car with it like that, knowing there was a coil/driver problem. It will be one of those tings though that will just go one day, not on and off.

The thermal pads were there stock.

From your last post, I'm guessing plugged cat came loose?

[bmwman91]

I bought the car with it like that, knowing there was a coil/driver problem. It will be one of those tings though that will just go one day, not on and off.

The thermal pads were there stock.

From your last post, I'm guessing plugged cat came loose?

Sadly, it isn't a bolt-on fix. An exhaust valve seems to not be closing fully. A compression test on cylinder 2 shows zero; the needle does not even bounce. The other cylinders all show good compression. There is a lot of soot and oil in the port so it is hard to tell what the real deal is with the engine in the car, so I'll get a better look on Saturday. Now that the disappointment has settled and I am thinking clearly, I am working on having it all addressed with the engine builder. I'll pull it this weekend and ship it out on Monday.

I assume that this is a one-in-a-million fluke. The builder is the most respected BMW engine builder in the country, as far as I can tell. They are 100% behind me on this and are basically offering to rebuild the whole head for me at no charge, and have the whole engine shipped back and forth. I don't want to put too many details out in public because I know that their reputation is very important to them, and they are definitely behind me on this. I will be very curious to see what caused this...usually stuff like this happens at first-start or maybe months later after running it at redline for extended periods. 75 miles of gentle driving under 5000RPM...weird.

[bmwman91]

Also, according to the BMW service manual for the 318iS, it says that coil packs that look like the epoxy filler has melted/oozed out indicate a bad ECU. It seems most likely that the driver ICs are crapped out, although I am not sure what other biasing circuitry there might be behind the drivers. I wonder if there are any transistors currently in production that would be viable substitutes for these ones? It would be awesome if there were so that we could all replace our aging ECU components without having to deal with a stand-alone installation.

Regarding the TSM's comment about melted coil packs, I have noticed that every year or two a coil seems to get wonky and they all have a little bit of oozed plastic/filler. I am not sure if that is because of the ECU, or because the M54 coils are not designed to use the same dwell period as the M42 ones (I invented the M42 coil on plug conversion back in 2006 & have been running it ever since).