M20B25 wont start, no spark

[Daan]

Hi there.

Recently drove our e30 into the garage for some weight stripping. Removed the dash and went through a lot of the interior wiring removing what we thought was unnecessary, and also done some welding in the passenger footwell, near the fusebox and where the loom comes through into the cabin.

Im pretty sure the fusebox is alright because I was keeping an eye out while my dad was welding and nothing caught fire etc.

And the interior wiring we removed was mostly just speakers/headunit/interior lights/trip computer etc. so dont think any of that will have affected engine wiring.

The ECU was unbolted but not unplugged, and the first time we tried to start the car it was just cable tied in place. I have since tried earthing the ECU case but that made no difference.

The car turns over great but has no spark. Follwing that back to the power cap, the positive terminal on that has something like 0.54v when cranking, so presumably that is the problem, however the power cap positive feeds straight from the ECU, which is where im confused.

Does the ECU have a power supply which I could have inadvertently knocked out in the engine bay or a feed through something else which may have been unplugged?

All fuses in the engine bay fuse box are fine.

Any help is much appreciated, thanks!

[Grrrmachine]

And the interior wiring we removed was mostly just speakers/headunit/interior lights/trip computer etc. so dont think any of that will have affected engine wiring.

This is almost definitely where the issue is. The "trip computer" (13-button OBC) is connected to the start circuits and sometimes acts as an immobiliser. If you rip it out, you need to bridge the connection you removed.

Have a read of this:

http://www.e30zone.net/e30zonewiki/inde ... Green_Wire

[Daan]

Thanks for the reply. Been out in the garage since I posted earlier and decided to investigate the DME Relay. Turns out it wasnt switching 12v to the ECU when then ignition was turned on. Checked the 2 smaller activation pins, one was supplying 12v as it should, the other (ground, obviously) was connected to ground but had 45k Ohms of resistance! Replaced the earth wire to a good earth spot and tried again, still no luck. Then tried bridging the 2 larger terminals (pin 30 and 87) to bypass the relay, and still no joy. However, I have just realized there are 2 pin 87's, and I only bridged to the larger one. First thing to try after dinner is bridge all 3...

Thanks again, Dan.

[Daan]

Okay, so bridging all 3 pins did not do anything. Still no power at the Coil and obviously no spark.

Next thing im thinking is to check the ECU is getting power, after reading the Wiki it seems pin 26 gets 12v and grounds through pin 36 which activates this relay and then sends a signal back to pin 37.

I pulled the ecu plug before I came in to check the terminals and familarise myself, but accidentally done it with the battery still connected, hopefully thats not done any harm...

More quality time with my multimeter tomorrow morning!

[Daan]

To conclude the thread, it was to do with removing the OBC and associated loom. Just found the 2 green wires into a single white plug up near the glovebox, and bridged the two wires together. 12v at the coil and therefore a spark and running car

Only problem now is the ICV is buzzing constantly, unless you disconnect the battery. Probably due to me bridging/disconnecting/playing around with loads of other wires and relays, hopefully get that sorted tomorrow evening!

Cheers.

[jimbom30cab]

thanks for the conclusion Dean, i learnt something interesting there.

[goosiegander]

Despite having a break from M20 ownership i still have 2 pf the little loop plugs...

Glad you solved it