M635 no spark - so confused, help!

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

M635 no spark - so confused, help!

Post by nicklondon »

My M635 decided a few weeks ago after I left it for a week that it wanted to cause problems with starting - sometimes no problem and sometimes it just turns over (no spark - she's deffo getting fuel!)

Since then both crank sensors have been changed, the ecu went off to be rebuilt (worked a couple of days after this and then went back to how it was) and the dme relay changed and still no love from her. Sometimes (very rarely) starts on the button but usually just turns over and won't start, won't even give signs of spark.

Any help is seriously appreciated as I'm getting very stuck now. All the usual stuff has been checked as well, coil etc.

Thanks for all your time
wattsmonkey
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Re: M635 no spark - so confused, help!

Post by wattsmonkey »

The m30 no start guide on forum5 is good, along with the motronic guide linked on this site: the m88 isn't very different.

I know from much personal experience that it's very easy to miss the obvious! A mate had the most frustrating intermittent starting problem which was as simple to solve as the main earth strap from engine mount to chassis rail being loose.

The guides listed might help with a systematic check of each and every basic test.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
Reevo
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Location: Hampshire, UK

Re: M635 no spark - so confused, help!

Post by Reevo »

Hi there,
Just wondering if you had any success resolving this no start issue? - I've recently been having a very very similar issue with my '89 M635csi, which has now been of the road for a frustratingly long time with it:

To begin with it was an intermittent issue - it occasionally wouldn't start and even conked out while driving once, and took a while to re-start. Then it would only fire on occasion, mostly just turning over with no spark, and now it won't fire at all.

The garage has been working through all the electrical components - including struggling to understand the three different engine sensors and how they interact with the engine management system to provide a spark...

Just wondered if you'd solved this problem and had any ideas we could try...
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Stoffie
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Re: M635 no spark - so confused, help!

Post by Stoffie »

You can program a code in the obc to prevent the car from starting. I would imagine something wonky in that circuit could also cause some very erratic behavior.

Ignition switch can also cause some serious trouble.
The M88/3 was all about power, no cats. At idle the raw fuel from the exhaust will make your eyes water like an old V-8 powered muscle car's exhaust did.
wattsmonkey
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Re: M635 no spark - so confused, help!

Post by wattsmonkey »

Reevo: if it conked out whilst driving as well as the intermittent faults you're describing then the main relay would be the most likely culprit before checking everything else.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
Pod
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Re: M635 no spark - so confused, help!

Post by Pod »

+1 on that!
BenM635i
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Re: M635 no spark - so confused, help!

Post by BenM635i »

I had issues with my 6 related to the OBC stopping the main relay. On occassion would turn over but no spark...

Found the issue in the end after much pain. There is a 'relay' box in the passenger side dash which is linked to the OBC, its part of the security system. If the OBC code is set then the OBC stops the 'box relay' closing on start up.

However the little box likes to break, the relay fails to close so no spark.

I just removed this box, connected pins 3&4 together and no more issues.

Might help, worth eliminating anyway.
'85 M635 #160
Reevo
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Location: Hampshire, UK

Re: M635 no spark - so confused, help!

Post by Reevo »

Thank you very much all for the helpful suggestions.
Seems to have been fixed now, which is very good news, by a combination of replacing the main relay and one of the crank sensors.
Reevo
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Joined: Fri Sep 22, 2017 12:26 pm
Location: Hampshire, UK

Re: M635 no spark - so confused, help!

Post by Reevo »

Or, it would appear, not actually fixed after all.
Apparently it started a few times straight away, but now no longer. So all further ideas of things to try welcomed as it’s a real shame for the car to be sitting unused and unusable for so long,
baders
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Re: M635 no spark - so confused, help!

Post by baders »

The best idea we can give you is for you to download the ETM, grab a reliable multimeter, and get to fault finding. We can help you from there.
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
baders
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Re: M635 no spark - so confused, help!

Post by baders »

Oh, and put your car details in your signature. That also helps us help you :wink:
1986 635csi LOCUTUS / Arktis Blau Metallic / Pearl Beige / S38B36/ Close ratio dogleg 5sp
2002 E46 M3 / Topaz Blau Metallic / Black Nappa / 6 speed SMG software tuned / Bilstein PSS10 Coilovers / CMP RACP reinforcement
BenM635i
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Location: St Albans, UK

Re: M635 no spark - so confused, help!

Post by BenM635i »

Mine was intermittent no start too, did it for years before i fixed it - mechanic couldnt resolve it either.

Check the OBC relay box i described, one under your P2 dash.
'85 M635 #160
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