22 replies to this topic

[victorludorum]

I'm trying to solve a starting/running problem with my 2000 mpi and I've removed the MEMs unit. One of the connectors is scorched, although the fuse is still intact. Is there a way of testing the connector block with a multimeter to see if it's still ok? I'm guessing that the associated relay is probably dead or damaged. Is it possible to open the unit to have a look, even though the whole thing will probably need replacing (as seems to be the case if I understand correctly)?

[FlyingScot]

Do you mean the MFU (multi function unit) next to the servo?
If so have a look at the pinned thread http://www.theminifo...-functionality/

It's an SPi one but the principle is the same. I have an MPi one kindly donated by a member which I haven't gotten around to photographing the innards of (sorry John!)

FS

[victorludorum]

Thanks so much for that I can confirm that it's the fuel pump lug that's cooked, so I'll have a go at opening it up tomorrow and getting my multimeter on it...

 

It worries me a bit that if I order a new unit, it may just get fried again if the problem is elsewhere, and they're 50 odd quid I believe. It's a bit odd that the fuse is intact, so maybe it is normal for the connector to cook when the relay itself goes.

[FlyingScot]

I think you find their a bit more than £50 if your talking new.

Trace the wiring once you have metered the coil and contacts would be my advice AND the fuel pump ( could have seized although should have blown the fuse as you wrote)

FS

[spiguy]

Most likely area for the wiring to have chafed through and caused this, is where the cables leave the MFU and pass next to the clutch master cylinder pipe. Have a good look at them here and anywhere else they pass metal parts and edges - I mean look closely, it could be a 1mm area where it's rubbed through (that happened to me and burned out tracks in the MFU).

[victorludorum]

I'll trace those wires later today. For the moment I'm struggling to get the MFU unit open to have a look inside!

[FlyingScot]

The last ones are very difficult to open (TRW ones) as they are glued and clipped.

FS

[victorludorum]

Ok, all done. I had to break the tabs, but that's ok. The coils are all intact, but the solder joint was blown for the fuel relay, so I put a bit of solder on there and bingo, it's running again and seemingly running well. There didn't seem to be any obvious rubbing of the cable sleeve, so I imagine it was related to something else. I still have an electrical problem somewhere as the battery is only putting out 12.8 volts when running at 3000 rpm with all the electrical loads turned on, but hopefully this fix will allow me to get to Dieppe from Paris so that I can get the car to Sussex Road and Race for a full check-up.

 

I'm wondering if in some way I have caused these electrical issues I'm having as I used to cut the battery just after shutting off the ignition. I don't use that car much at all and the battery was drained after a month like many MPIs I believe, so installed the circuit breaker. It may have been that I was pulling the power too soon while the ECU was still shutting down, and doing this consistantly has caused a fault.

[victorludorum]

And of course, thanks a lot for the input chaps. You've saved me a lot of arseache as always

[Guess-Works.com]

Check the current draw by the pump, and also the condition of the fuel filter on the rear subframe...

 

If the pump is tired it'll use more current to pump the necessary 3 bar pressure, and if the fuel filter is block/restricted it'll also use more current to provide necessary pressure..

[spiguy]

Glad you have got it working again. When you say the joint was blown, do you mean burned out? Just that when you say you got it fixed by putting a blob of solder on there, it could be just that the joint was a dry joint and so it cracked round the joint causing poor connections, and possibly higher current - that would most likely happen if the power feed was cutting on and off briefly due to bad connection, causing repeated high start up currents.

 

I would still spend some 'quality time' double checking the wiring for any chafing, and be inclined to put some external insulation around the cabling as it leaves the MFU in any case, I have found that the plastic coiled 'cable tidy' type products are quite good for this sort of thing, though don't have that too near to any hot engine parts of course. Also make sure you are getting good contact on the pin to connector connection on the affected pin on the MFU, as you said it was charred.

 

Have you by any chance tended to run the car very low on fuel? The pump is cooled by immersion in the petrol in the fuel tank. Due to the way it is installed in the tank, by the time you get to the red line on the gauge, the pump is borderline for being partially uncovered and so cooling is not so good. If you run the car in the red on the gauge it can actually burn the pump out. Before burning out, the pump will start to draw a high current - I have had this happen where it popped the fuse (I think it is a 20A fuse as standard, but could be 10, can't recall). I didn't know about this situation at the time, and assumed the fuse had just been weak as when I put a new fuse in, it ran again (stupidly of me I put a higher rated fuse in as that was all I had). The pump ran again for a few minutes then it burned out. I had been running the car (it was off the road) with only a little fuel in the tank just to warm it up every so often. Just thinking that if you have been running it low on fuel, then there could have been a higher current draw. I would check the fuse rating and see if it is correct, if you have a haynes manual it should show the correct value.

 

EDIT: Good tip from Guess Works  - if you don't know when the filter was last changed, or suspect it could be clogged up, change it.

Edited by spiguy, 24 June 2015 - 09:06 AM.

[victorludorum]

I've tried to change the fuel filter, but I can't get it undone, hence it's on my list of stuff for Kevin to do at Sussex Road and Race. I imagine it's in a pretty bad way as the car's done 45,000 now and has probably never been changed...

[victorludorum]

Access to the pump seems very limited. Is it possible to measure the draw without shifting the tank?

[FlyingScot]

You'll probably need to make up some flying leads if you don't want to move the tank a bit.

The MFU stays powered up for a short time after shutting down, but it's more the issue about the current draw from the pump as discussed above.

FS

[spiguy]

You could insert your current measurement at the inertia cutoff switch on the bulkhead under the bonnet. Most multimeters will have different inputs for different current ranges - often a 1A or 2A input and then a separate 10A measurement depending on the meter, you need to check what you can measure and remember it is an inline measurement so you want to break into the wire not measure across it (although that would actually still work *IF* you are measuring at the inertia switch end but not at the fuel pump end - see the next paragraph below for an explanation). I am guessing but I think a 10A range would be best, though I can't imagine the pump is 120W - that's a lot of heat to lose through the fuel as a coolant, but I would think it could be more than 1A. Really am guessing though. The meter should have fuses in it's current measurement line.

 

Another advantage of measuring the current draw up at the interia cutoff switch is that if you accidentally do put the meter across the two wires instead of inserting it in series in one of the wires (which is what you should do) then all you would do is bypass the inertia switch, since at the switch it is just the 12V feed in then back out and off down to the pump, whereas at the pump end you have one wire which is 12V and the other is ground). If you made that mistake at the pump end then you would short out the 12V feed and this would certainly blow the meter fuses and possibly do other damage, at least it could blow the pump fuse in the car.

Edited by spiguy, 24 June 2015 - 12:34 PM.