Starts but won't run.... - The Unofficial BMW M5 Messageboard (m5board.com)

Mfiver · 30th June 2009, 02:16

No sooner had I got the master cylinder sorted (earlier post refers) than the very occasional cutting-out problem has come back - this time with a vengeance.

Trundling back home along the M4 from doing the master cylinder I noticed a couple of high-speed hesistations when on a constant throttle. Many years ago with a Granada 2.8i Ghia X (showing my age now!) something more acute was the sign of a knackered fuel pump.....

The next weekend I was intending to take the car to Wales for a few days - I travelled all of 3 miles (it was a very hot day - the car had been driven in the morning and had been standing out for several hours) and the car just cut out at 30mph and wouldn't start again.

It cranked over rapidly but just wouldn't catch: no spark or fuel, I thought.

The AA man had a look at it: the sparks were good but there was no fuel (it caught with a whiff of carb cleaner). Eventually he decided that the likely cause was a short in the wiring loom to the injectors: his little LED test lamp showed he had two positives at an injector when he should have had a positive and a switched earth.

No way was it going to go: and his towbar would have wrecked the air dam so it was a case of waiting another hour for a ride home on a recovery truck.

Whilst waiting for the latter, the car had cooled: of course I had a go at starting it. It didn't run, but it did start momentarily before dying.

Rolled it onto the drive at home: by now I was very late. My garage is small and requires a reverse downhill approach - there is absolutely no spare space. However, I didn't want to leave the M5 on the drive for a few days.....so I tried starting it. And to my relief it started immediately and ran for a couple of minutes while I put the car away and then switched off.

That was at the end of May: last Friday (four weeks later) I finally thought I should have a look. Well, of course it doesn't go - whilst it cranks fine and catches, it won't run as the key is released to the run position.

BeforeI investigate the injection loom, I think it's much more likely to be a failed electrical component - a relay (main or fuel pump) or perhaps a crank position sensor. I suppose it might even be the ignition switch....the fuses are OK though.

So for starters, which kind person can tell me which relay does what? I have three mounted on the inside face of the fusebox and three mounted on the front face....

All constructive suggestions gratefully received!

Regards

Mfiver

batmobile · 30th June 2009, 09:52

I would check this:
take off all the covering of the electric plugs of the injectors, i think that could be a worn cable (as was on my 735i motronic).

Mfiver · 15th July 2009, 01:29

Batmobile,

Many thanks for the pointer. I had looked at the cost of a new engine bay loom on realoem and had frightened myself silly! Was your 735i afflicted on just one injector or on all?

The AA man seemed to think it was a loom fault: however, I still don't see why it will catch when cold and then not run - but not run at all when hot.

At least with the car reversed into the garage I can get at the wiring: all I need is time: perhaps I should book some annual leave!

Any/all additional constructive thoughts much appreciated!

Regards

Mfiver

davettf2 · 15th July 2009, 09:09

Hi Mfiver
Is it narrowed down to sparks or fuel, after it refuses to start have you tried the old trick of laying a spark plug against the head to check for sparks. I know it is not scientific but it may help.

best of luck
dave

batmobile · 15th July 2009, 09:20

Quote:

Originally Posted by Mfiver

Batmobile,

Many thanks for the pointer. I had looked at the cost of a new engine bay loom on realoem and had frightened myself silly! Was your 735i afflicted on just one injector or on all?

The AA man seemed to think it was a loom fault: however, I still don't see why it will catch when cold and then not run - but not run at all when hot.

At least with the car reversed into the garage I can get at the wiring: all I need is time: perhaps I should book some annual leave!

Any/all additional constructive thoughts much appreciated!

Regards

Mfiver

It was just one injector cable, dicectly before the plug, a 2 minutes repair time, check it out.. maybe..

Mfiver · 16th July 2009, 23:17

Davettf2,

It's definitely lack of fuel - AA man confirmed nice healthy sparks using the method you suggest - and it ran on a brief whiff of carb cleaner.

Something is nagging in my mind that the fuel pump is running when the engine is cranking but stops when the key is released to the run position. This seems like it might be a relay to me. Or even the ignition switch. I need to go and look at the Bentley manual again.....

This does not explain why the AA man got two lives at the injector connector when he should have had a live and a switched earth. That points towards Batmobile's thoughts.

Aaargh! Just need more time!

Many thanks

Mfiver

James (Jim) Knight · 17th July 2009, 06:39

Many years ago I had a similar problem on an '88 535i that turned out to be the ECU.

davettf2 · 17th July 2009, 09:23

Hi Mfiver

Another couple of quaint thoughts, can you remove a fuel pipe and verify pump running when it cannot build up a back pressure to the regulator, also when the AA man checked the injectors, did he check all. Also is the power to the injectors a switch to earth or a switch to power. If a switch to earth this may be the ECU as it would need to pull down the rail when operating, thus two lives at the injector.

best of luck
reagrds
dave

Mfiver · 3rd November 2009, 00:58

After a long pause....

Davett2,

The AA bloke checked only one injector. It appears it is a switched earth so I just hope it's not the ECU! I did wonder if the crank position (speed) sensor was faulty as if there is no signal, the pump will not run.

I have done nothing with the car for many weeks....too much family stuff getting in the way.

However....

My central heating boiler is in the garage and developed a fault. In order to get to the boiler to reset it, it was necessary to move the car....heck, I'll crank it on the starter if I have to, I thought.

Cranked the engine....same as before, it fired but stopped when the key went back to the 'run' position. Tried cranking again...and big no-no...put foot on throttle. Kept cranking and it eventually started.

Tried it again today when the gas engineer arrived to fix the boiler....and it started. Ran it till it was hot, then let it idle until the gauge needle rose just above normal and the electric fan kicked in. Then switched off to let it heat-soak, because I think it may be temperature-related. And it started. And then let it cool....and it still started.

So now it's back in the garage and I seem to have an intermittent fault. Very irritating. The car has now run out of MoT and was SORN'ed a couple of months ago, so I will try and book it in in the next few days and risk a trip to the test station....

Any more thoughts?

Regards

Mfiver

davettf2 · 4th November 2009, 09:21

Hi Steve

Oh bother!! Just what you don't need. I supose one question is did you need to floor the throttle on the second restart, another is when it started the first time, floored throttle, how much 'cr*p' came out of the exhaust. if no and lots respectively did you have a bloked injector or two?

Other than that I would just keep checking it starts on a regular basis, I assume you will keep the car off the road till spring, thus a quick run up and down the drive will be the order of the day.

regards
davettf2