The Case Of A Blowing 30amp Fuse!!

I recently experienced a problem with FUSE 6 (30 AMP - Engine Management System) blowing on my 2000 1.8 Mpi. In fact another forum member was experiencing the same problem.

Like me the Engine Bay Overheat - RED light glowed momentary (less than 1 second) , the engine would die, blow a fuse or it would suddenly start up again, and all would be OK for a while. Sometimes it would blow a fuse, I'd replace it, switch on the ignition and the 30amp fuse would blow straight away.

Thinking it might be water in the ECM, Main Relay or connectors I would strip them down spray them reassemble and all would be fine. I even drove nearly 400 miles without any hiccups. The following day as I came to set off, I let out the clutch..POP blown fuse. Anyway in discussion with Rob Bell (F Register) I eventually this evening, found the culprit and you might want to just check your vehicles.

We touched on something in one of the threads, that it must be electrical, possibly linked to the starter circuit. And it was, but perhaps not where you'd think it might be. Over the weekend I'd checked the wiring to the ECM and all the connectors and the main relay again. I'd cleaned and sprayed, I'd jiggled, pulled, tugged and twisted all the cabling and connectors with no adverse effects. I then drove off the drive all was well, and then all of a sudden I'd slow down for a junction, accelerate away and there it was, it would suddenly cut out and start up again.!!! It id this a few times over a 20 mile round trip. It wa sdifficult to replicate, that wa sthe annoying thing.

Buit one thing was certain it was all related to engine movement, because underneath the air intake pipe to the throttle body, there are a couple of metal coolant pipes. One has the additional bleed screw on it, know the ones?

Well ,in close proximity to these pipes is a major wiring loom that goes to the starter, throttle body etc etc. It was only as it was getting dark tonight, that with a little bit of feeling around and pulling and tugging with the engine running, that I happened to touch this loom and lo and behold the engine suddenly spluttered and there was a brief spark. If it hadn't been going dark I doubt if I would have seen it.

Switching off the engine and disconnecting the earth to the battery I un-ravelled said loom and found to my horrow that it had been resting on the hot coolant pipes and had melted thro' a couple of wires and as the engine moved, as when changing gear, starting off or even going over a bump, it was enough to short out on the coolant pipe either blowing a fuse or cutting out altogether.

Out came the soldering iron, small lengths of cable shrink wrap etc. It wa sa pig to do but do it we did.

I wonder if the original forum member who started this thread has the same issue. In fact, I wonder how many MGF's out there have perhaps not noted that a cable clip or tie is missing, allowing said loom to rest on the hot coolant pipes!!!


Tone

Great detective work, Tone. :broon: :clap:

I'm sure this will have a lot of people checking said loom! :dry: :yesnod:

I thought I'd share a few photo's with you of the offending loom in question.

In the light of day it appears that a cable tie may have become broken /removed for whatever reason allowing said loom to sit on top of the coolant pipes and had melted the outer plastic conduit and eventually had melted thro the cables within.

The photo's show the position of the cable and where I believe the cable tie should be as now shown.

Cable under Pipe from air filter


Easily seen without intake pipe


Cable tie fixed to bracket on coolant pipe.


There are two fixing points this is the second one ensuring loom is kept off coolant pipes


This is where the loom was resting on the pipe and eventually melted thro'. How long this had been going on I've no idea. I never noticed it.


This is the fuse it kept blowing (30 amp) in my case No6, but I believe in later models this maybe No2





It might be worthwhile you checking your loom as it is quite a tight stretch and is a little awkward to reach. At the weekend I will remove the engine cover again and disconnect the loom from the various sensors allowing me to redo the loom and add more of the protective covering and tidy it up a little more in daylight to ensure I don't have any further issues.

Like I say I don't know how long it's been going on like this. The only time the loom may have been moved was when the head gasket was done along with the cam belts and pump 12 months ago.

Guys just check yours when you can the clip/tie could have been missed broke I don't know but it caused me enough headaches.