M635CSI not starting

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

Post Reply
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

M635CSI not starting

Post by Bobo W »

First up my mechanical knowledge falls into the numpty category so please be gentle - I need to pass your information onto my friendly mechanic

Nov '86 M635
Car started no problem earlier in the week but now just turns over - doesn't catch at all
Battery is fully charged
Petrol in tank but no obvious smell of petrol in engine bay after turning over

I'm assuming that I'll need to:
- check if there's a spark - should be relatively easy
- check fuel pump is working - hoping my mechanic knows how to do this but at least I know where it is :lol:
- check fuel pump / main pump relays - again hoping my mechanic can do this - from reading other posts I believe these are under the dash, but where exactly / how do we get at them?

Is there anything else we should be looking at?
Steve
1987 M635CSi #388
daz635
Posts: 102
Joined: Sat Jul 20, 2013 7:26 am
Location: Brisbane, Australia

Re: M635CSI not starting

Post by daz635 »

Hi Bobo

Have a read thru this document explaining how to trouble shoot the different parts of the Motronic injection system it's clear and easy to follow

http://www.hiperformancestore.com/motronic.htm or https://drive.google.com/open?id=1X2hPj ... fDnugVsk9N

A no start problem can be caused by many issues including Sensors, relays, grounds, wiring, Fuel Pump, DME issues.

As you have said the first job is to check for fuel and spark. Can you hear the fuel pump prime when you turn the ignition on?

If not maybe start by checking fuse number 11

Let us know how you go. There is a wealth of knowledge here
'86 Euro 635 #1887204 Schwartz (086) Buffalo Schwartz Interior
Image
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

Re: M635CSI not starting

Post by Bobo W »

Thanks

In these links and various other images on line it shows the fuel pump relay attached to the fuse box yet from reading posts on here, I believe I should be looking under the dashboard (late 86 car) A cursory look doesn't reveal anything so where should I be looking?
Steve
1987 M635CSi #388
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

Re: M635CSI not starting

Post by Bobo W »

Ah so now it gets interesting 8)

So being the aforementioned mechanical numpty I adhere to the adage of self healing problems so if you leave it the problem will resolve itself.

Well not quite in this situation but the absence of any help has led me to consider ringing the RAC to come and fix. As my garage is somewhat inaccessible from the main road I thought it prudent to move it the car in preparededness should it need to be towed. Anyway, once moved, I tried to start one final time and lo and behold, after a bit coaxing, we had life, albeit lumpy to start, but then smooth running.

Does this indicate some dodgy electrical connection?
Steve
1987 M635CSi #388
wattsmonkey
Platinum Member
Platinum Member
Posts: 1649
Joined: Mon Jul 16, 2007 2:58 pm
Location: Cheltenham, U.K.

Re: M635CSI not starting

Post by wattsmonkey »

You need to remove the kick panel under the steering wheel: four Philips screws. Relays will be right in front of you, attached to ecu bracket. My opinion is that they should be changed as a matter of course. Not expensive from dealer.

The motronic document referred to above is superb, most of it applies directly to the m635.

The ignition switch is a likely culprit from my experience of intermittent no starts, but your mechanic will be able to rule this out easily by jumping the starter motor.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
nicklondon
Posts: 22
Joined: Mon Jan 26, 2015 11:51 am
Location: London, UK

Re: M635CSI not starting

Post by nicklondon »

I had this problem and it was resolved by a new DME relay which as whattsmonkey said is under the steering wheel. Make sure you buy a new one from BMW and not one of the usual culprits (Euro Car Parts etc.). I bought one a few weeks back from my local dealer and it was 50ish quid.
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

Re: M635CSI not starting

Post by Bobo W »

Thanks Gents, I'll let you know how I get on.
Steve
1987 M635CSi #388
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

Re: M635CSI not starting

Post by Bobo W »

Here's a quick update on where we are.

The car is still not fixed but it looks as though the problems have been identified.

So anyway I got the car started and took it to Classic Heroes - Initially the car was found to have a very weak spark which was down to a crack in the coil body and the distributor cap and rotor arm were very burnt on the internal contacts.

While the car would start fine almost every time, roughly every third start, the car would suddenly flood itself and belch unburnt fuel out the exhaust. The only way to start the car then was to remove the plugs, dry them out, replace and then restart.

CH removed the fuel rail with the fuel injectors to enable them to watch the fuel delivery from each injector. They found that on the third start attempt the fuel injectors just poured and dumped fuel which is what was causing the car to occasionally flood. By swapping over the ECU from another car the issue went away. So my ECU has been sent away to be repaired and then we'll see where we are.
Steve
1987 M635CSi #388
Bobo W
Posts: 46
Joined: Tue Sep 06, 2016 8:11 am
Location: Kent

Re: M635CSI not starting

Post by Bobo W »

And still we are no closer to a fix.

Classic Heroes sent ECU away for repair but no fault found. Fitted ECU back into car and same old problem. Next step is to put "my" ECU in other car to see if problem replicates itself. Suffice to say plenty of head scratching going on in Buxted
Steve
1987 M635CSi #388
Post Reply