No start issue

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528i-1981
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No start issue

Post by 528i-1981 » Tue Nov 26, 2019 3:51 pm

Body work done (passenger front wheelhouse).
Welder transferred the coil, the ignition control module and the ballast to the new wheelhouse.
AFM was removed during work as was the ECM from the glove box.

Car acts like it will start but dies. Fuel pressure to the rail is OK.

I guess I'll check the grounding and then swap out each of these with on-hand spares to see what's up, but if any one of them is especially suspect let me know and save me some time. I suspect it's a ground on either the ICM or the resistor.
(oo=00=oo) Eric
1981 528i Manual

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Lock
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Re: No start issue

Post by Lock » Wed Nov 27, 2019 2:55 am

Seeing as the work was done by the wheelhouse and I don't believe in coincidences, I would suspect the ignition system.
Is it the classic - starts for a second then dies? That means the cold start injector is spraying fuel, but once you stop cranking it stops too, for a second or so of running. Which should indicate the ignition system is firing. Can you get a timing light on a spark plug line and ensure spark is okay?
You can bypass the resistors for testing. The third wire is just a tap from the starter for cranking high voltage burst. I know it sounds obvious, but check that everything is plugged in - 3 ballast wires, ignition module seated firmly, the small signal cable from the distributor to ignition module, AFM, are the big ones.
The ECU gets timing signal from the coil. That black wire goes - coil, ignition module, wire back to fuse box, through firewall to tach, across dash to ECU. Make sure that lone black wire in the glovebox by the ECU is plugged back in too. If that doesn't get there, the ECU won't have timing and won't fire the injectors. I have experienced a weak coil that is out of spec, can spark but doesn't seem to send a workable signal to the ECU. Replaced the coil, started right up.
Hopefully nothing was zapped during the welding.
If all those basics are okay, and tapping the AFM flap runs the fuel pump, and the spark plug leads are in the right places, you should have something.
1979 528i 5-speed conversion G260/6, Motronic 1.3 179
1980 Honda CX-500

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528i-1981
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Re: No start issue

Post by 528i-1981 » Wed Nov 27, 2019 5:33 am

Gah! I forgot about the lone black wire to the ECU. I bet that's it - yes it seems to be starting normally and then dies, so no signal to the injector is entirely consistent. Body guy was careful not to get the welder close to anything, which was my concern as well. Thanks Lock. Happy Thanksgiving to all and God Bless First Fives!
(oo=00=oo) Eric
1981 528i Manual

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