E21 Fuel pump relay repair and ignition modules

[David Mc]

Now that our cars are getting on a bit, things start to break down - a common problem seems to be fuel pump relays, which after doing some research I found can cost from about US$35 to 96 Euro to replace. The good news is that these things are repairable! Basically the relay contains a small electronic timer circuit, a few resistors, diodes, a couple of transistors, maybe a capacitor and a small integrated circuit along with the actual relay coil. I had a couple of dud relays laying around and since most of the components inside them are super-reliable, I just decided to test the coil and see if it would pull the contacts in, then troubleshoot the electronics. The small "555" integrated circuit which is the heart of the relay timing function can be bought for around AUD$1, as can the 2 other likely troublemakers in the circuit - the transistors, so I invested $6 and after about 20 minutes of soldering, now have 2 working fuel pump relays.

The relay itself looks like a completely sealed unit but it isn't - turn the thing upside down and carefully slide a little jeweller's screwdriver down the inside wall of the case and you will find it is clipped in position by a couple of little tabs that can be released by prying the sides of the case outwards. The complete relay circuit will then simply slide out of the bottom of the case. I will post a few pics as soon as I get around to it, but needless to say, once the repair has been done, you can simply clip the relay and attached board back into the case and no-one would ever know it had been apart.

After doing some troubleshooting on my car, I eventually diagnosed a faulty ignition control module - on the '82 323i this is BMW part number 12141266702. Since replacement Bosch modules can cost up to US$180 each, here are a list of reasonably priced alternative brands and part numbers:-
Bosch part number 0227 100 123
Alternative Bosch W0133-1614014
Hella 5DA 006 623-001
Fuelmiser CM413
Cambiare VE520221
Tridon TIM017
HÜCO 13 8001 (A German Ignition component manufacturer, owned by Hitachi Automotive -5 Year conditional Warranty!)

As far as attempting to repair the original Bosch ignition module goes, forget it - I opened my non-functional module up and could only recognise 3 diodes and one transistor, everything else was on microscopic integrated circuits bonded to the circuit board and the whole enclosure was filled with sticky silicone.

[Jeroen]

Useful info sir! I was hoping you were going to offer repaired relay assemblies here but sadly not

As for ignition control modules: there are some simple causes:
- getting wet causing short circuits
- overheating due to corrosion at the bottom
- circuit breaking due to a high current on the ground side, on its turn caused by a corroded ground connection

What I did two years ago to prevent this: remove ignition control module, remove heat sink. Clean up surfaces, refit with fresh heat dissipating paste, and place back with a fresh ground screw and make sure contacts are corrosion free on module and chassis. While at it, check the module connector and cable connector (both 9 pin or something) for corrosion as well.

[David Mc]

Thanks Jeroen, yes my ignition control module looked great - it even still had the rubber water-proofing boot in place, but when I measured the resistance to ground it was astronomical, sadly this caused the module to fail, so I replaced it and did the full screw thread cleanup and coat the base of the new module with heat sink paste. The car started better than it has started for the five years I have owned it - I had already rebuilt the Warm Up regulator, additional air slide, replaced both fuel pumps, calibrated the injection system and replaced the inductive coil in the bottom of the distributor, so it's no wonder it's going like a new car.

[Jeroen]

Great end result then!