Fuel System M535 - The Unofficial BMW M5 Messageboard (m5board.com)

blountation · 21st July 2009, 09:21

Hi Guys,
(This is my first post, so bear with me!). My '86 M535 is having issues and i'm pretty sure they're fuel related. The car had been sitting for about 4 weeks the other day and it started as normal after the rest. I drove it down to the local shops for it's first drive after the rest and it started and ran fine. I went and did my shopping and came back (the engine still had heat in it) and turned the key and it sounded like it was running on about 2 cylinders. I instinctively turned it off again before having another go at starting it, but it wouldn't fire at all. With no other option i rang roadside assistance and organized them to come. After waiting about 40 mins, i tried starting it again and it started as normal and ran fine. I let it idle up to temp and gave it a rev and it was normal, so i drove it home (about a 5 min trip). It started running rough not far from home. I got it into the garage and it was missing a bit, but still running. I had a go at starting it while it was still hot but it wouldn't start, however i've tried it since and it started when cold. I thought it might have just been a bad batch of fuel and was going to test drive it this morning, but it wouldnt start or fire at all. I'm thinking of checking the filters and pumps. Can you tell me where these are? Any other ideas?
Thanks guys.

Sebring NL · 21st July 2009, 11:46

The problem probably lies in the fuel system relais .

Many people tell me they never have electronic trouble with E28's, but I maintain quite a few professionally and they frequently have trouble with the relais surrounding the fuse box under the hood. A strange fact is that , even on M535i's of the same exact age, the relais setup all look different. I have an Alpina B7 and two M535i's standing next to eachother, and had an E28 M5 and E28 535i in the shop two days ago. On all cars, the relais were in different places next to the fuse box.

Solution : Get all the relais surrounding the fuse box new. Some of them are not fuel related, but also for instance the lights relais fail frequently. This is the cheapest , first step. If things don't work out, check the fuelpump for operation. Its located underneath the back of the car and is cylindrical shaped , covered in a thick rubber sleeve. The pump looks shiny with plastic blue/greenish finish. Simply put a battery on the + and - and you'll soon see if it works. It can pump both ways so make sure you put the cables on correctly!!!

If the relais are new, pump works and still no result, check if the ECU makes the pump kick in. I once had to make a new wire from the ECU to the wiring harness ( check elec scheme, I think its pin #21) because it had failed somewhere for some reason.

good luck!

Wout

blountation · 28th July 2009, 04:09

Thanks for the comprehensive reply Sebring! I will explore all those avenues, but i was just wondering if you could tell me where the fuel filters are located on the car? I just have a niggling feeling that that's where the problem lies (because the car was sitting idle long enough for some rubbish to settle in the fuel). I think the filters would also be a cheap fix?

davidoli · 28th July 2009, 10:55

The main fuel filter is situated just to the right of the fuel tank when looking from underneath the car from the rear and looks about the size of a bean can with a petrol pipe connected to both ends .

There may also be a micro mesh type filter at the base of the fuel pump inside the tank itself .

D

blountation · 28th July 2009, 16:50

Thanks David, i'm really impressed with the quality of responses in this forum. i'll check the filter and see if i get any love. If not, then it's onto the relays....
Angus

blountation · 12th August 2009, 09:02

Ok guys, ive got a further question: What is the fuel pump(s) layout on the m535? i had an e30 325e and it had 2. one as a primer inside the tank and another pressure one under the car infront of the left back wheel. Is it the same with this charriot?
Also, if it does have the two pump layout, which do you think could be the problem? The car will start and run. i've had it idling for about 10 minutes before the problems start to arise, where it starts missing and hesitating under any throttle. Eventually it won't run at all unless it is left to cool. Ideas? Thanks all.

Sebring NL · 13th August 2009, 12:14

stabbing in the dark won't help

have you already replaced the relays?

you have to narrow things down here