My M635 is eating main relays

[DRPM635CSi]

Three drives and three dead main relays afterwards. I've now run out of sources for the old style 4/5 pin relays that go under the steering wheel valence. The one that powers the fuel pre-pump in the fuel tank.

Any ideas? I've got no idea what's going on, but my car is seemingly eating main relays. Weirdest thing I've ever seen on this car and no-one I've talked to so far has any clue where to start looking. Best recommendation so far is take it to an autoelectrician and let him rip it apart piece by piece until he finds something wrong. Naturally enough, I'm not keen on letting a rabid baboon with a multimeter go nuts ripping apart my car's interior on a wild goose chase.

Nothing else is going wrong. No fuses blown, the fuel pump works OK when it has power. The car runs fine when I install a new relay, but after one drive, that relay is dead and the car then won't restart again. No fuel = no fuel pump power = dead relay. Help.

[hornhospital]

I'm not keen on letting a rabid baboon with a multimeter go nuts ripping apart my car's interior on a wild goose chase.

Hey, I resemble that remark.

This won't find the problem, but I wonder if disconnecting the battery immediately after the run would save the relay? Or does it refuse to restart immediately after turning it off, as in something kills it WHEN YOU TURN IT OFF? I'm guessing the relay stays engaged after you shut the car down.

[Bhart]

It would be interesting to know which side of the relay dies? The control side or the load?

FYI; The control signal (low amperage) flows between terminal #85 and #86 on the relay. The load signal (higher amperage) flows between terminal #30 and #87 on the relay. Quite simply the low voltage side of the switch turns the high voltage switch on and off. When power is removed, both switches should switch off on the standard relay. Staying on for extended hours should not be outside the design parameters.

If I look at the schematic for my '87 (thanks to Prospero for the large typeface) I can see that the fuel pump relay is controlled by the DME computer on #85 and goes to ground via #86. The main power comes in on #30 directly from the battery. Power comes out on #87 and goes through a fuse #11 and on to the fuel pump. The power signal from #87 also goes directly to the O2 sensor relay low amperage circuit #86. The O2 circuit is not separately fused.

[L6inHouston]

Hi, guys, I'm struggling to reassemble the wiring under my L6's dashboard after "mechanics" removed panels and disconnected things without labelling anything. Anyway, I found a 5 prong relay on the floor and can't find a corresponding plug. From the electrical diagram, I suspect this is the main relay. If so, where does it plug in?

[Brucey]

Hi, guys, I'm struggling to reassemble the wiring under my L6's dashboard after "mechanics" removed panels and disconnected things without labelling anything. Anyway, I found a 5 prong relay on the floor and can't find a corresponding plug. From the electrical diagram, I suspect this is the main relay. If so, where does it plug in?

does the car run? If yes then you don't have a missing main relay. If 'no' then you might do.

cheers

[Brucey]

BTW if the contacts are burning out in the fuel pump relay then you could have an intermittent dead short in the power feed to the fuel pump and/or a fuel pump that is on the verge of stalling (eg through a bad FPR or a blocked filter), and is therefore drawing far more current than normal.

cheers

[RossDinan6]

It would be interesting to know which side of the relay dies? The control side or the load?

FYI; The control signal (low amperage) flows between terminal #85 and #86 on the relay. The load signal (higher amperage) flows between terminal #30 and #87 on the relay. Quite simply the low current side of the switch turns the high current switch on and off. When power is removed, both switches should switch off on the standard relay. Staying on for extended hours should not be outside the design parameters.

If I look at the schematic for my '87 (thanks to Prospero for the large typeface) I can see that the fuel pump relay is controlled by the DME computer on #85 and goes to ground via #86. The main power comes in on #30 directly from the battery. Power comes out on #87 and goes through a fuse #11 and on to the fuel pump. The power signal from #87 also goes directly to the O2 sensor relay low amperage circuit #86. The O2 circuit is not separately fused.

Bold is corrected to clarify.

[DRPM635CSi]

Update: Car has been to workshop for a week and of course didn't fault once while it was in there. See attached workshop invoice and scans of fuel pump relay current draws.
https://www.dropbox.com/s/cyilcp4zps3up ... .pdf?raw=1

So the problem does not appear to be the relay at all, but something else. I have just started the car again after a couple of weeks away for work and it did start, but reluctantly. Another problem might not be helping the situation. My engine appears to have lost its ability to step-up the throttle when cold. The engine idles very rough and very slow @ <500rpm, when stone cold. It is OK when warm, but cold starting is hard and I basically need to feather the throttle while cold to keep her running happily without misfires. What should I be looking for to cause this lack of throttle step-up when cold please?

I am travelling to South West Florida in November and was wondering if there are any board members living near Fort Myers who wouldn't mind taking delivery of whatever parts I need to fix my car that I could pick up from them for stuffing in my luggage as I'm coming home? I fly out of Fort Myers airport to Dallas-Sydney-Perth.

I'm looking at needing three sets of Wagner brake pads, a driver's door seal for an E32 plus whatever parts are needed to fix the issue described above. Can anybody in Flo-Rida help a guy out please?

[Brucey]

Idling slowly suggests 'not enough air getting into the engine' and/or a catastrophically weak mixture and if it won't take any throttle that also suggests a weak mixture.

It may be no single fault but several in combination. For example if the ICV isn't working properly this might lead to a small airflow through the engine, and this in turn might cause the AFM to operate in a range where it doesn't measure accurately for some reason.

Bad fuel pressure, air in the fuel lines, sticky injectors, poor feed from the main relay... all these things might cause the problems you see.

A good test is to (after the car has been standing a few days) to run the fuel pump by putting a jumper in the relay. If this immediately results in gurgling in the fuel line, it is pretty certain that you have at least one tiny leak in the fuel line, and that this will allow air to bleed into the fuel lines whilst the car is standing. NB the resultant fuel leak under pressure won't always be noticeable at first. Most of the air in the fuel lines will be swept out as soon as the fuel pump runs, but it will still leave bubbles in places and these will result in erratic fuelling for a while on a cold engine.

cheers

[DRPM635CSi]

This problem has turned out to be nothing at all to do with the relays but rather a dying fuel pump just ahead of the RR wheel. I took the car for a long drive the other day on arrival back from being away for work for 6 weeks. She started fine getting out of the garage. Started again straight away at a first stop along the way. Second stop to drop something off though and although the engine was only switched off for ~3 minutes or so, no start. All the cranking speed in the world, but not even a cough.

Removed the relay and shorted the pins with a paperclip listening carefully for what the fuel pump was doing. I could actually hear it under stress trying to spin, but not quite getting there. A few more tries and eventually it broke free of whatever resistance there was stopping it spinning and it started whirring away. Replaced the relay and started the car normally. I suspect the pump motor has a weak or dying brush or pole on it and whether it starts or not depends entirely on what position it stops in when I switch the car off.

[Brucey]

when you stop the car for a few minutes then odd things can happen; for example the fuel in the fuel rail can boil inside a hot engine bay and this can (if the check valve in the pump is bad) push the fuel back through the pickup lines. Remember that the pressure will get to 3bar before it opens the FPR.

Once you get vapour in the fuel lines/pump the car won't start until the pump is able to pump liquid fuel again. It is quite possible that what you heard is the sound of the pump trying to pump fuel vapour not liquid fuel. The change in sound could have been liquid fuel getting into the pump again. [FWIW you shouldn't run a fuel pump for more than a few seconds if it doesn't have fuel in it; it will be neither cooled nor lubricated in the normal way.]

In normal running the fuel rail/pipework is only kept cool by virtue of the fuel being pushed through it. This is one reason why fuel delivery is so important; not only does a healthy flow past the FPR mean that you will have more consistent fuel pressure, but it also means the fuel system will be kept that bit cooler in normal running.

There are a lot of minor faults that don't give big trouble by themselves but together they can cause big problems. For example a bad check valve in the pressure pump, and a tiny (smaller than a pinprick) leak in a fuel hose can lead to bad problems. The fuel in the fuel rail will try and boil whenever the (fully warmed up) engine is stopped. The bad check valve (and few are so perfect they will withstand boiling fuel in the fuel rail BTW) will let fuel get pushed out of the fuel system backwards. The pinprick leak allows air in to replace the fuel vapour and the result can be that the fuel system is mostly full of air when you go to start the car. Needless to say it won't start or run well until all the air is purged out.

If the car starts promptly first turn of the key ('zikka-brumm' or 'zikka-zikka-brumm') even after a period of non-use then almost certainly the fuel system is completely leak free where it matters. [NB even if the fuel boils in the rail following a hot run, it will later cool, condense and pull liquid back into the fuel rail.] However when you have even a tiny leak then even after a short run and a week of non-use the car might not start promptly because the fuel rail is full of air not fuel. After a hot run it can be a lot worse than that because of the effects of boiling. Note that the size of the leak can be so small as to be virtually undetectable; no real signs of wetness on the outside of the fuel hose, just a slightly worse petrol smell than you might be used to. I found a leak in my CSI hose this way.

From cold, try running the fuel pump only; if there is a gurgling sound from the fuel rail, then it is certain that air is getting into the fuel lines and you need to fix it.

cheers

[DRPM635CSi]

This problem has turned out to be nothing at all to do with the relays but rather a dying fuel pump just ahead of the RR wheel.

Can anyone please help to identify this fuel pump for me? I'm looking for the long sausage fuel pump just ahead of the RR wheel arch but RealOEM keeps telling me it doesn't exist and there are no parts like that for my car (VIN 0760188). Pretty certain this thing has not been messed with or had any aftermarket stuff added to it, so I'm trying to find this fuel pump so I can buy a new one, but the part number elludes me.

Cheers

[plip1953]

Looks to me like an error with OEM. If you select a later car (I looked at a 1988 one) it will come up with part no 16141179232. Then click on that part and you will see that it applies to loads of model including your own. Don't take that as gospel because I don't have first hand knowledge of fuel pump differences between model, but that's the way it looks to me.

https://www.realoem.com/bmw/enUS/part?i ... 6141179232

[DRPM635CSi]

Thanks Phil, you're a champ. Just ordered from Rock Auto. Cheers