Last week, I struggled trying to get my 1989 E30 BMW 325i to start. It didn’t have spark. Could it be a bad ignition coil? My tech analyzed the coil using the numbers in the best source I know: the BMW manual published by Bentley (no relation to the car company of the same name). Sure enough, the resistance for the ignition coil wasn’t ideal. But, it wasn’t bad either. So, I wasn’t sure.

Fortunately, I have five (yes, that’s a 5) other semi-dead, mostly-complete E30s around here. I figured that at least one of them should have a healthy ignition coil. So, my tech went around, measuring the coils’ resistance. None was to spec, yet they weren’t horribly bad either.

Puzzled, I swapped one ignition coil after another into my non-starting E30. The car still wouldn’t start. Logically this proved approximately nothing.

Finally, I discovered the fault to have been a loose wire at the battery … the small positive wire was loose, and so the main relay wasn’t getting power. Once I fixed that, the car started.

But, it would have saved me some time had I known that my stash of ignition coils was good.

So, now that my E30 is starting, running, driving etc. I’m using it to test used parts. For example, I have swapped in another E30 325i ECU and I have tested that. For a test like this, I try to go beyond the obvious, so that the car doesn’t just start and idle. I drive it at normal speeds, at wide open throttle and so on … cold engine, warm engine … After several hours of driving on the alternate ECU, I concluded it was good and I took it out (one cable, four screws) again. Now it’s in my parts inventory as a known good item. I’m SURE it’s good.

Why stop there? I didn’t. 🙂

Today, I also swapped in one of the ignition coils whose resistance values was not perfect. I drove the car with the engine at 5500 rpm, accelerating, and the coil kept up just fine. So, I’m categorizing this ignition coil as one more good part. I’m SURE it’s good.

Next, the instrument cluster. I removed the one that used to be in the car because it had issues anyway, and I put in another one. The replacement is working very nicely. But, I don’t want to put back all the trim, just yet. Instead I plan to also test the half-dozen or so other instrument clusters that I have, that are currently “condition unknown.”

Ever since I started 3seriesparts.com I’ve always wanted to have this sort of thing — a car that’s a rolling parts test bench.

And now, finally, I do. I’m happy.