combo relay part number superceeded?

[woody6]

I'm new to this forum, but not to older BMWs. I'm helping out my brother-in-law with his 78 model 633. I have had a good bit of experience with the E28 based 6ers, but this is the first E12-based car I've had in my garage. As you might have guessed, the car starts, but dies soon thereafter. With my fuel pressure gauge attached, one can see why. The fuel pump runs when cranking, but not when the engine is running. I have verified continuity through the AFM switch, and ground at the ECU. The problem appears to be the relay (not surprisingly).

I've opened up the relay and do not see any bad solder connections. According to all the relay diagrams, it looks like pins 85 and 86b on the relay should close the points to power the pump when running. Testing the relay on the bench using a 9v battery, the problem appears to be the resistor that is mounted on the board between the relays (labeled R1).

I'd be happy to replace either the resistor or the whole relay, so here are my questions:

1. Does anyone know what value resistor should be there? (the colors are not so easy to read after 3 decades). Anyone ever done a resistor replacement on the combo relay?


2. The Bosch combo relay on this car is '0 332 514 105', it has 12 pins on it. No one lists that number anymore. The website for a parts vendor I use recognizes that number in the product search however, and recommends Bosh '0 332 514 121'. The picture and text for that relay show/describe the relay with 13 pins. Can anyone confirm that the 13 pin replacement will work for the old 12-pin relay? The part is about $60 and I don't mind paying if it fixes the car, but I really don't want a $60 relay in my toolbox for the rest of my life if it doesn't.

Thanks for the help, I'd already have been lost without the information on this forum.

[tschultz]

I ordered a new relay from ebay for about $50 a coupel years ago.

But when mine went bad, the car just did not run at all. Jumping the leading, and it started right up.

From your issue, it almost sounds more like you might have a bad fuel pump that is just on it's last legs.

[woody6]

From your issue, it almost sounds more like you might have a bad fuel pump that is just on it's last legs.

Thanks TSchultz, indeed I wish that was it. The start-but-not-run problem was the original problem my brother in law had with the car a year ago or more. The car has sat since then, and I only started working on it a couple of weeks ago. There was no fuel pressure at all, so a new pump was the first order of business to get it going. Now with that replaced, I'm apparently back to the original problem.

The only part of the combo relay that doesn't work is the part that keeps the pump going when the engine is running. I can manually close the relay and keep the car going. I've checked connections to the ECU and through the AFM door, and all are good. Bench testing the relay, I can see and trace the path that *should* complete the circuit, but the resistor appears to be bad.

It had occurred to me to bypass the resistor with a jumpered connection, as I just don't see the need for it (the resister). The diodes keep the fuel pump from engaging the starter, so I understand why they are required, but the resistor seems unnecessary.

If the $60 relay really is a Bosch service replacement for the OEM one, I don't mind the expense to fix it right. I just can't find confirmation of that anywhere.

[woody6]

The diodes keep the fuel pump from engaging the starter, so I understand why they are required, but the resistor seems unnecessary.

I found the (non-BMW) reference to Bosch combo relays in the link below. The author explains that the resistor I questioned is there to limit current flow through the AFM switch, so eliminating it might hasten the demise of the AFM, which of course I don't want to do.

http://www.ratwell.com/technical/DoubleRelay.html

[woody6]

Okay, for the *next* person that has this same concern, the 13-pin combo relay '0 332 514 121' (0332514121) DOES WORK in place of the 12-pin combo relay '0 332 514 105' (0332514105).

It was necessary to remove from the relay plugs on the car, a plastic piece that blocked the location where the extra relay pin would push into. Obviously, there is no wire from the harness to that slot in the plug.

The car started right up and fuel pressure was maintained after start.

[tschultz]

Great that you got it sorted! Always good to know which others work when this happens again.

Have you attempted to repair the old combo-relay? Been curious if anybody had luck with that repair, I haven't broken my old one open to try it yet.

[woody6]

Have you attempted to repair the old combo-relay? Been curious if anybody had luck with that repair, I haven't broken my old one open to try it yet.

In my old relay, the circuit that closes the relay when the AFM door is opened includes a resistor, and on mine that resistor appears to be bad based on testing with the old multimeter. I considered buying a resistor and attempting the repair, but even having read numerous BMW and non-BMW sites about the Bosch combo relay, none ever mentioned the proper relay resistance value (the stripes on the old resistor were not clear).

I suppose I could test the new relay and buy a resistor to match. I might do that to have a spare.

[Jeff Dennis]

Thanks Woody for your post I have to buy one.....glad to know what works.

[LandShark]

Dont know if anyone recalls, I bought a '0 332 514 121' relay for a Fiat Spider on eBay. It seems to just crank, no start. Im trying to locate a good spare for my current functional '0 332 514 103' metal can one.

Does anyone know a modern equivalent? Is the pre-Sept '77 that much different?