Combo Relays?

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canada karl
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Combo Relays?

Post by canada karl »

Is there a simple way to test a combo relay? Are they even available for a 530i? Where is the best place to buy one. I've read the Faq in the Tech forum about soldering the contact points.
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
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Mike W.
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Re: Combo Relays?

Post by Mike W. »

Testing would be difficult as I've heard they often fail intermittently. So it might test good today, but not tomorrow.

Availability? Dunno, query Realoem for a P/N and search for it. At worst I would think they would pop up on ebay every so often.
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1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
garyinwestoz
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Re: Combo Relays?

Post by garyinwestoz »

can they be split into 2 different relays? or does the function depend on the symbiosis of the the parts together.
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Mike W.
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Re: Combo Relays?

Post by Mike W. »

I'm sure there's a way to make 2 or more separate relays do the job, but I think they do interact with each other. It's hard to say for sure as most diagrams just show them as a box with leads, and one, very fuzzy one I've got on the computer that does show what's inside is hard to read and missing part of where all the wires go. Simplistically, it runs the fuel pump via the AFM and the thermo time switch. Sounds easy enough to bypass. Anything else? It's got a lot of leads to just be doing that.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
Nanajoth
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Re: Combo Relays?

Post by Nanajoth »

I've been dealing with a combo relay issue that was just recently resolved. I ended up separating the case on mine and tried to start the car while looking at the internals to verify they were working. Not very scientific, but it's an option.
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Mike W.
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Re: Combo Relays?

Post by Mike W. »

Nanajoth wrote: Wed Mar 22, 2023 3:45 pm I've been dealing with a combo relay issue that was just recently resolved. I ended up separating the case on mine and tried to start the car while looking at the internals to verify they were working. Not very scientific, but it's an option.
The problem with that is if it's a bad contact, as apparently happens, you can't tell by a visual.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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Lock
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Re: Combo Relays?

Post by Lock »

Mike W. wrote: Wed Mar 22, 2023 12:26 pm I'm sure there's a way to make 2 or more separate relays do the job, but I think they do interact with each other. It's hard to say for sure as most diagrams just show them as a box with leads, and one, very fuzzy one I've got on the computer that does show what's inside is hard to read and missing part of where all the wires go. Simplistically, it runs the fuel pump via the AFM and the thermo time switch. Sounds easy enough to bypass. Anything else? It's got a lot of leads to just be doing that.
From what I've seen glacing at wiring diagrams you're right. It powers the fuel pump, thermo time switch and optionally idle air valve when the AFM flap is open, then the other relay is the main power for the ECU as well, so all of the L-Jet sensors and outputs (power to AFM, injectors, sensors).

I can say it doesn't interact with the ignition system (despite being on that loom), that is just ignition source power branching off from the combo relay base to the ignition.

What sucks is they decided to make the L-Jet wiring all white, but somewhere I've got documentation in L-Jet functioning and it is in essense really just an electric version of a carburettor. The O2 sensor is the main piece that sets it apart though.

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Mike W.
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Re: Combo Relays?

Post by Mike W. »

Yes, it emphatically does not interact with the ignition. I was having problems at one time with a bad FPR flooding the engine when cold. I mean flooding as in no start. I was able to unplug the ECU in the glove box, then hit the starter and it would start and run briefly as it burned off the excess fuel. Being a little bit warmer, probably mostly the plugs, once the ECU was back in the loop it would immediately start.

Now the ECU does get a signal from the ignition telling it when to pulse the injectors, but the ignition doesn't know what the FI is doing.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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