M42 No Start - Electrical Issue

[jolle21]

Hey folks - hoping I can get some advice on where to start with my electrical issue.

I have an M42 swapped E21 (1980 320i) and everything was running great, but then I let a friend drive the car.... lol bam problem number 1! Shouldn't have done that.

Anywho, there were no problems with driving the car, we got it back home, and when I went to go for my own drive, the car didn't start and there was a popping noise coming from the coil packs. Pics below show my setup, the coilpack 1 is closest to the firewall, then 2-3-4 going out to the front;



I popped the hood, tried to start again, and the popping noise + what appeared to be sparks coming from coilpack number 1. As for the car itself, the lights work and other electrical components expect the engine.

The starter doesn't click and engine doesn't turn over. I'm pretty sure I fried my harness, but can anyone let me know what happen and where I can start my repair?

Thanks!

[DesktopDave]

Are the sparks coming off the primary terminal (little connector) or the secondary (plug wire tower)? I'd think you have a hard short in that coil. Unplug the harness from that offending coil and try to start the car.

I'd think that your harness is OK. If you get the car running on three coils, I'd recommend taking the DME out to have a look at the coil driver transistor.

[keflaman]

And I have some spare coils laying around if you need 'em.

[jolle21]

Thanks guys....and it was a no go with unplugging the harness on coilpack #1. Still no start...there's only a click from my fuse box. No starter, no nothing.

Thinking the DME is fried? When you mention the driver transistor, would I have to open up the DME? The terminals on the DME look fine when I unplugged it, nothing looked burned.

Also, there are no more popping noises nor any sparks. Pretty sure I BBQ'd something....lol woooosah, wish I broke the car, it would be easier for me to intake the situation hahaha. I appreciate the help guys, enjoy the weekend!!!

[jolle21]

Do these relays look burned up to you guys?



One appears to be fuel pump and the other is dme...if I'm not mistaken.

The other is a green one which I think is for o2 sensor and that one had cleaner looking prongs, but these looked burned to me. Also, when I shake the white one, it has a small rattle...I'll start there and see if that had any issues. Probably should be safe and get a coil too huh?

[Tgoode318]

Yes you should replace those. I fixed the dme relay on my car by taking sand paper and cleaning the contacts tell they shown silver/gray recently and it fixed my instrument cluster about 98 percent which wasnt working. The only thing not working on my instrument cluster now is the mpg which some times works and sometimes dosn't. I just went ahead and ordered a new relay to see if it will fix every thing for good. For your no start problem it would be a good first cheap step to replace those.

[DesktopDave]

I've had ones that looked like that and still worked fine. It's best to replace them though; of course keep those two with the car as spares. I also carry jumpers meant to short the main and FP sockets. A rattle isn't cause for alarm - the internal return spring or contact arm can be a bit loose after years of work. I'd definitely clean up the contacts with a bit of contact cleaner and a pencil eraser, cellulose buffing sponge or brass bristle brush. I avoid using steel wool on smaller electrical contacts.

The orange Bosch 456 on the left is the FP, the white 5-pin one is the main relay. Be careful to match up the circuit on the main relay. Those sometimes require diodes and resistors; there is some confusion about the proper part number that I haven't yet resolved.

[jolle21]

No go with new relays. Still no crank, no start. Going to have the starter and alternator tested. Saving up for some new coil packs....but at this point I'm suspecting the ECU is done for....my fuel pump doesn't make any sounds or anything. Nothing engages....

The only  thing that works are the cars electrics. (Eg lights)

Definitly shorted something. I'm thinking there was a spike in voltage. This must of burned something out in the ECU. Does that sound probable?

No spark and no fuel make E21 a dull toy....

[DesktopDave]

Do you have a check engine light wired up? If so, does it turn on with the rest of the lights? That'd be a good sign your DME is good. You should be able to run a stomp test next, see if any codes are set.

How's the battery? Nice & healthy, above 12VDC? Did you get a load test run on it? If it's voltage is too low, the BMW undervoltage or unloader relays will prevent the car from starting to protect the alternator & starter. That could be the click you're hearing.

One more thing I forgot to mention. Do you still have the 20 pin diag port hooked up? There's a remote start function that can bypass the key switch and inhibitor relays (if installed). Get yourself a nice chunk of 12 or 14 gauge wire and short pins 11 to 14.

[Tgoode318]

Yah i didn't think that would fix it but like i said a good cheap/free place to start. Any time i'm inspecting a suspect system in these old cars i like to fix/repair any thing that is really showing age, especially when its free like cleaning the contacts! Following Dave's advice above is going to be your next step. If you Could get any codes out of her it might help us in diagnosing your problem.  Also Most automotive places (autozone napa etc..) will test your bat/ alternator for free in the hopes of you buying one from them.
GL!
-Tg

[jolle21]

Thanks guys!!

As for diagnostics and codes. I still have the diagnostic port, however, being a 1980 E21, they didn't have engine check lights, so I can't get any feed from the DME.

I did do my own version of a stomp test though....lots of vulgar language, don't recommend it 

In terms of wiring, I'm only connected by the following through the C101 to the E21s fuse box.

Oil Pressure Switch
Fuel Pump Power
Alternator Exciter
Switched Power to O2 sensor heater
ECU Power
Starter Signal
Coolant Temperature (Gauge)
Tachometer

Everything else is negated since the e21 is wired up differently.

Meh, no worries....I did refresh the internals of the m42, but the electronic related stuff is fairly old, plus I'm using a duralast battery that dura-don't-last, I'm sure the spike originated from there, killed a coil, sending a failure to the DME's ignition module. The battery had to be charged every few days, I'm gonna say that's where my culprit lies....on that day when my first attempt to start failed, I immediately thought it was the battery, i got it charged and still no start. My first attempt after my friend drove the car had to have shorted the coil.

So I'm going to start with a coil pack....thinking about just going COP to eliminate the spark plug wires...might as well get a spare DME. If both work, I can MarkD chip one of them....

But again, thank you for all the help. I'll keep you guys posted on what happens.

[Tgoode318]

Jolle21 i would definitely run some test on your battery first before you do anything else if you are strapped for cash!  Other wise buy away because the COP is awesome (and so is mark d ) IMHO though this is the next step for you because as you said its dura crap lol.