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M635 cutting out

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nicklondon
Posts: 22
Joined: Mon Jan 26, 2015 11:51 am
Location: London, UK

M635 cutting out

Post by nicklondon » Mon Feb 04, 2019 10:25 am

Hi All - I have been battling with an issue that's been ridding my M635 for a while and I really need some help.

I put the car in the garage about a year ago as I just didn't have the time for it and now I would like to get it running 100%. Basically it just cats out or wont start at completely random intervals. Hot, cold, mid journey, parked.. it's completely random. I have changed the whole ignition system, from coil to plugs to dizzy, I've changed the position sensor, had the ECU refurbed, changed the relays..

I also got her running on the weekend, she fired up stayed on for about 5 mins and then cut out. A high pitched buzzing noise was coming from the engine compartment and the tach was bouncing around.. I couldn't work out where the bussing was coming from but I could feel some vibration coming through the fuel rail. Looks like the pump is feeding fuel correctly as well.

Any tips on what to look for next!? Thanks in advance!

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whiskeydry
Bigcoupe supporter
Posts: 116
Joined: Tue Oct 30, 2012 12:34 pm
Location: Midlands, UK

Re: M635 cutting out

Post by whiskeydry » Mon Feb 04, 2019 1:48 pm

Hi Nick
My M635 does get laid up regularly and sometimes for long periods. I have learnt over the years that, after disconnecting the battery, it is prudent to spray as many engine management system electrical plugs and sockets with contact cleaner as you can reasonably access before taking the car on the road. By doing this you are able to check all the connector pins and spades to see if they are corroding or damaged. I use fine wet & dry to clean spade contacts if they look grubby. I also remove and reseat the relays and fuses. By doing this I have eliminated some spurious problems and also discovered a couple of issues that needed attention. The symptoms you describe are similar to ones that I suffered from for a while and it turned out that there was a loose pin in the main fuse box plug that supplies 12v to the coil (thick green wire). Suggest that if it cuts out look for 12v on the coil to eliminate this as a potential issue. I have also had to replace the Crank Position and the Pulse generator sensors as the plugs were beginning to fall apart, again causing similar symptoms. Also worth checking ground wires for good contact. I know there are far more knowledgeable people on this board that may be able to offer you better advice than this but at least it might give you something else to look at.
Best of luck with it.
Phil
Current
1985 RHD M635csi #128
1999 E36 M3 Evo Convertible
2010 E91 320d Touring

Previous
E32 735i
E28 525E
E24 635csi
E28 525i

nicklondon
Posts: 22
Joined: Mon Jan 26, 2015 11:51 am
Location: London, UK

Re: M635 cutting out

Post by nicklondon » Fri Feb 08, 2019 11:26 am

Hi Phil,

Thanks for your response. I'm going to have another crack at it tomorrow. I think you've offered great advice.

nicklondon
Posts: 22
Joined: Mon Jan 26, 2015 11:51 am
Location: London, UK

Re: M635 cutting out

Post by nicklondon » Mon Feb 18, 2019 2:12 pm

All sorted! It was a dodgy DME Relay!

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sansouci
Bigcoupe supporter
Posts: 1636
Joined: Mon Jul 08, 2013 10:52 pm
Location: New York City

Re: M635 cutting out

Post by sansouci » Mon Feb 18, 2019 6:21 pm

That was mercifully quick. How'd you find it?
Sansouci
84 E24 633Csi Auto, Bronzit/PearlBeige 6997510
93 E32 740il M60 Auto, Alpenweis/Ultramarine
60 528i M30 5-speed Green/Beige (crushed)
71 240Z 4-speed White/Blue (rusty & sold)
65 396 Chevelle 4-speed, Marina Blue/Black (stolen)

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whiskeydry
Bigcoupe supporter
Posts: 116
Joined: Tue Oct 30, 2012 12:34 pm
Location: Midlands, UK

Re: M635 cutting out

Post by whiskeydry » Mon Feb 18, 2019 7:06 pm

Well done! Glad to hear your M6 is back on the road. :D
Current
1985 RHD M635csi #128
1999 E36 M3 Evo Convertible
2010 E91 320d Touring

Previous
E32 735i
E28 525E
E24 635csi
E28 525i

nicklondon
Posts: 22
Joined: Mon Jan 26, 2015 11:51 am
Location: London, UK

Re: M635 cutting out

Post by nicklondon » Sun Feb 24, 2019 6:03 pm

All I'll say is make sure you buy these major relays from BMW and NOT after market sellers (Euro Car Parts etc.).

I have an old Porsche which was doing the same and my Porsche mechanic took a quick look at my BMW - he noticed it was not an original BMW relay so I got one from my local dealer and the car runs like a dream now.

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