5 replies to this topic

[K999TUL]

I have been having intermittent fuel issues with my Mpi over the last few weeks.

Originally I had thought that the fuel tank was contaminated because the first time it happened was after driving through cobbled streets... 5 minutes later popping and juddering and engine cuts out. Try turning over but no ignition. Left for 10 mins, try again, car starts. Drive for 500 meters and same happens again. I assume that the cobbled streets have loosened rust/shaken up some crud in the tank.

Get the car recovered.

Next morning go for start, no issues, running fine. I assume that anything that had been stirred up in the tank had settled overnight.

So I removed the tank, flushed it through, changed the fuel filter and ran through some Redex equivalent.

Took it for a drive yesterday ran fine all day. A good 50 miles covered. Went home, mini had a rest for 2-3 hours. Jump back in and head out on the road again. 2.5 miles later the same issue as before, erratic rpm, popping and banging in the exhaust until finally cutting out... again, I can leave it a while and go for start, it turns over and struggles to get ignition but eventually does after however many tries. When it fires up it is lumpy and the idle is hunting slightly. Drive 500 meters and the same again.

...

This morning I have a crack at it. Straight away go for start, it fires up but idle is a bit lumpy and is hunting slightly. Go for a bit of throttle action and it climbs nicely (kind of) to 2000rpm where it goes ape s**t once more - popping banging, misfiring all over the place and stinking of fuel, but doesn’t cut out (the popping actually set off the car alarm of a car parked nearby - it was pretty loud). Ease off the revs and it returns to idle. Do it a few times to make sure and it keeps doing the same thing. I knock it off for a while and go over some easy checks.

Earth bonding - no apparent issues
Spark plugs - no apparent issues - cyl1 slightly sooty but negligible, none are wet (didn’t do a visual check of spark)
Sensor wiring - no apparent issues
Air filter off to check throttle body operation etc - No apparent issues


Go for a start again, this time appears to be a bit less lumpy. Give it a bit of throttle action once more but this time I am limited at 3000rpm with only a few signs of misfiring. Keep trying and the same thing - limited to 3000rpm, kind of lumpy.

Knock it off, have a poke around for 5-10 mins and have another go. This time limited to 4000rpm and it’s idling a little smoother still. Keep trying but still always limited to 4000rpm...

Knock it off to pull sensors and fire up with them out one by one to see if I can replicate the original problem upon coming to the car first thing this morning (2000rpm and misfiring/popping).

No real change when starting up - each time with a different sensor removed (other than IAT as this made it idle much faster than usual, and ECT as this set the going from ignition on).

All back together again and go for start up aaaaaand....... running nice. No limit in place, idling pretty nice and revs up to 6400rpm as normal!

Now, I am new to Mpi models having never owned one prior picking this one up a few months ago. I have gone through the workshop manuals and taken as much information from them as I can... but aside of what I have already done what else is there I can do to get to the bottom of this?

It seems to keep cropping up out of nowhere. It will run fine with no issues for a couple of weeks then this happens. It’s clearly nota physical fuel issue as I first thought, so that points to either injectors or sensors I guess??

I know there are some real knowledgeable fellows on here and wondered if anyone could point me in the right direction (or a better direction than the path I have taken) as my next step is to begin swapping out sensors beginning with HO2S, MAP and so on... oh and try to pick up a code reader off of fleabay - suggestions as to which one I should be looking for are more than welcome!


By the way, it is my daily driver but work is walking distance luckily!

Thanks in advance!!

Ben

[Sprocket]

I've been looking at an SPi recently with similar problems.
 

I suspect your problem lies with the fuel pump and associated control system. It's not uncommon for the fuel pumps to die, and they do so in many ways. It could also be the fuel pump relay in the MFU (Multi Function Unit, or relay pack as most call it). It could also be, like the car I'm looking at, a fault with the ECU causing the fuel pump relay to drop out which exhibits almost identical symptoms you are experiencing.

 

When you experience the cutting out, and when it refuses to start, can you hear the fuel pump prime for a second or two when you turn the ignition off, and then back on again?

Be sure to check all wiring,from the relay pack (brown/grey), to the thirteen way connector on the bulkhead (brown/grey), to the fuse box (brown/grey), to the inertia switch (white/purple), to the thirteen way connector under the dash on the passenger side (white/purple), to the connector on the fuel tank (white/purple) and finally the fuel tank ground on the passenger side rear light cluster (black). In that order!

 

Trip and reset the inertia cut off switch to be sure its making good contact.

Swap out the MFU (relay pack) to eliminate this as a probable cause.

 

another fuel unrelated issue can be a faulty crankshaft or camshaft sensor which can prevent the engine starting, usually when the engine is warm.

[Chris M]

I had a very similar problem with my MPI &I found the multi earth block up in n/s of the engine bay corroded. I took it apart & cleaned it, took it for a drive & was unable to the replicate the fault on a short run. I wasn’t convinced this was the cause so
I then decided to replace the coil pack, crankshaft sensor & camshaft sensor.
When I went to replace the crankshaft sensor I gave it a very slight turn & it broke so easily. The body has coroded & seized in quite badly.
I’m convinced that this was the cause I drilled it out & renewed it & I’ve took it out loads since & been ok.

[K999TUL]

Sprocket, Chris,

Thank you for your replies. These are things I will certainly have a look into - probably this weekend.

The trouble with checking the fuel pump is that I have to wait until the particular issue of cutting out and not firing up again arises to be able to see if it is priming at the point of not firing up when cranking, might be tricky to confirm or deny this is the issue as it is really out of the blue when it starts to do this. Also, it seems a lot of the time the mini is running really rich which leads me more towards a sensor malfunction. However I will definitely have a good poke at it and see what I can come up with and report back.

Are there any sensors that if faulty they would cause the MEMS to limit revs to 3000 or 4000rpm?

Are the any complications that might arise from me removing sensors for a clean/inspection? Other than things possibly disintegrating like your CKS Chris.

[Bat]

Hi,

It does sound like a crank or cam sensor problem.

The rpm limited situations are a clue to this.

Of course changing the sensor may cure it but it could be a wiring problem.

Anything said in relation to your problem is guess work without any diagnostic information from the engine ECU.

Cheers 

[K999TUL]

Hi Gents,

Thanks for your responses. Big help in fault finding.

So, having had a poke around without many answers, I hadn’t had any problems since the last time I posted on here u TIL yesterday - Granted I haven’t been driving the mini much through fear of becoming stranded without knowing for sure what the issue is.

I took the mini out for a spin yesterday and managed to “reproduce the fault” on the autobahn, right in the middle of some roadworks where there wasn’t a hard shoulder in sight... cue lots of angry faces from bmw driving Germans...

Anyway, based on sprockets speculation about the fuel pump I started there. Fuel pump was definitely priming each time I turned the key to stage II. Engine was firing up and idling but going apeshit when revved up to 2k rpm. Knocked it off and gave it another go, same story.

Had a poke around at the CMP plug and wiring, fired up, same story.

Had a poke around and bit of a wiggle of the plug and wiring on the CKP, fired up, hey presto. Full rev range to 6400 rpm no bother. Drove home with my fingers crossed and did the 50 miles without a hiccup.

So, it seems it is definitely the CKP or parts there of.

First thing I’m going to do is get some contact cleaner (none on the shelf at the minute ?) and have a good clean of the plug and contacts.

I will also give the CMP plug and contacts a good clean too seeing as I had some Rev limiting issues...


if it rears it’s head again, I will dress back the wiring and make off the plug again, and if that doesn’t cut it I will replace the sensor altogether.

Thanks for the direction gentlemen.

Ta, Ben

Edited by K999TUL, 23 September 2018 - 06:20 PM.