Engine splutter at random intervals - advice please

[Sykopaf]

I've recently had to be brought home on the back of a low loader when my fuel pump just died.

So I've had the pump out of the tank, fitted a new one and the car runs again.

But occasionally it'll splutter like it wants to cut out, and at the same time the MPG gauge at the bottom of the dash shoots all the way up to max and then back down again.

It does this quite a lot on startup and even once it's calmed down it'll drive ok 70% of the time then have a splutter.

Also, and this may or may not be related, there's suddenly a whining noise from the engine bay, like a supercharger whine. Difficult to pinpoint where it's coming from with the bonnet up but it seems to be somewhere towards the front drivers side.

When investigating briefly with Doug, we found the fan belt had quite a bit of play in it, but I didn't think that would be the cause of the whine. Doug thought it could also be alternator?

Any advice appreciated.

Cheers.

P.S. it's an M30B35

[jimbom30cab]

my alternator whines, it's more like a gentle squeel

[Speedtouch]

Perhaps there's some crud in the fuel tank, or fuel hoses, causing an intermittent blockage.

Have you replaced the fuel filter recently?

Or is it perhaps a loose CPS sensor cable rubbing against the fan pulley?

[Sykopaf]

Perhaps there's some crud in the fuel tank, or fuel hoses, causing an intermittent blockage.

Have you replaced the fuel filter recently?

No but that was the same line of thinking that I had. My pickup did something similar not too long ago (minus the whine!) and it was as simple as a blocked fuel filter.

That's gonna be my first port of call.

[Brianmoooore]

For the stutter, open up and clean the contacts in the DME relay, or replace it.
The source of a whine is likely to be the alternator, but I can't tell you if it's a death whine or no from here. Check that the drive belt isn't too tight, and consider running the engine for a minute with the belt off to narrow things down to the water pump or alternator.
Check that the fan viscous coupling isn't locked solid.

[Sykopaf]

For the stutter, open up and clean the contacts in the DME relay, or replace it.
The source of a whine is likely to be the alternator, but I can't tell you if it's a death whine or no from here. Check that the drive belt isn't too tight, and consider running the engine for a minute with the belt off to narrow things down to the water pump or alternator.
Check that the fan viscous coupling isn't locked solid.

Cheers.

I've got a fuel filter coming tomorrow but will check out the DME relay after work tonight.

Will try and get some video/audio of the whine too.

[Brianmoooore]

MPG gauge uses a road speed signal from the speedometer and a fuel rate signal from the ECU. If the gauge goes to max. it's getting the speed signal but not the fuel rate signal (car is moving, but not using fuel = infinity MPG).
The fuel flow isn't actually measured - it's just assumed that for a certain length of injector pulse, a certain amount of fuel is used, so, if the gauge goes to max. it's losing the injector pulse.

[Sykopaf]

I have absolutely no idea where the DME relay is, I can't see anything in the engine bay that looks like what comes up on Google images for E30 DME relay.

But, I have had all the big fuses out of the fuse box on the n/s of the bay and reseated them. This may or may not be a coincidence but afterwards it fired up without any issues. I took it for a quick test drive but it is still spluttering.

I took this video of the whining noise, it's not great but you can hear it when the camera gets close:

[Brianmoooore]

DME relay will have five pins and will probably be white. On a M40 E30 it's one of three behind the bulkhead wiring cover, and on a M20 engined car it's again one of three, under a cover on the wing beside the air filter, but on a M30 converted car it could be anywhere, depending on what the engine loom came from.
None of the relays and fuses in the fusebox, except for fuse 11 (fuel pump), has anything to do with the running of the engine.
When you find it, you can check if its the culprit by removing it and using short wire links to join together pins 30 and both 87s of its socket, then driving the car like this.
Remove the links when you stop the engine.

[jimbom30cab]

on an M30 the relays are really close to the wiring harness plug to the ECU so I would look under the dash first. There should be an orange (fuel pp) and white (dme)

could have quite easily been knocked during some high speed diffin ...eeer I mean whilst being fitted

[Sykopaf]

Found it! Under the dash like you said. Took it out, looked like it had a little oil in there, I clean it up, reseated it but still has the splutter. Will try short wire later and let you know.

[jimbom30cab]

have you checked your battery connections are tight, i know it sounds a bit obvious but i had a totoya avensis i drove about in for years which occasionally wouldn't start, it was so occasionally i never bothered to do anything but after a year or so i realised when i fitted an amp i had forgot to tighten the -ve terminal.

is your engine earthing all good also ?

[Sykopaf]

Yeah, that's all good. I keep thinking back to the whine though, if the alternator is on it's way out could that cause the issue?

[Speedtouch]

I suppose it could, if it happens to be knocking out spurious electrical impulses that may upset the ECU.

The other possibility is that it is not charging enough to maintain sufficient power to the ECU, so it is 'dropping out' and not firing the injectors or ignition coil properly.

[jimbom30cab]

It could be and another m30 driver on here had similar issues iirc that we're sorted by fitting a replacement alternator

Mcbonio I think is the user name, have a look in the m30 build threads

[Sykopaf]

Forgive my caution, I'm a newbie to this.

Is this right for the short wiring?

[Sykopaf]

When you find it, you can check if its the culprit by removing it and using short wire links to join together pins 30 and both 87s of its socket, then driving the car like this.
Remove the links when you stop the engine.

You sir are a genius. This seems to have solved it.

It stuttered once or twice over the course of the test drive but smoothed out the longer I was driving.

So I guess I just need another relay then. I'll pop into my local BMW servicers, see if they have one in stock