Starter Motor Circuit Disaster
Discussion
Hi Guys,
Thought I was just putting the finishing touches to my rebuild and I went for the first start and I've had a bit of a disaster.
Everything electric was working (fuel pump priming fine etc). When I cranked the engine over it sounded very lazy like it had a flat(ish) battery. It would only crank for about 5 seconds before stopping. I thought it might still catch so I carried on (for rather too long it turns out). Smoke started coming from the passenger footwell and I've melted some wires.
The melted wires come from the negative battery terminal and are spliced into two black wires of the loom immediately after the ECU. The loom looks like it might be ok but I guess the spliced in section was an inferior grade of wire. I assume this will be wiring for the alarm since it looks like an after-thought. I'll post some pictures later as I'm at work right now.
I've now checked the battery and it was reasonably fully charged.
I'm not sure what the cause is but I would guess it's an earth that isn't working properly (maybe the new chassis powdercoat is insulating it).
If the engine was too stiff for the starter to turn over; could that cause this effect or would the starter just not turn it over? Not sure why this would be but this was my first full engine rebuild.
Anyone any thoughts of the likely cause? What should be the normal path for electricity to return from the starter to the negative battery terminal?
Cheers,
Simon (feeling somewhat deflated)
Thought I was just putting the finishing touches to my rebuild and I went for the first start and I've had a bit of a disaster.
Everything electric was working (fuel pump priming fine etc). When I cranked the engine over it sounded very lazy like it had a flat(ish) battery. It would only crank for about 5 seconds before stopping. I thought it might still catch so I carried on (for rather too long it turns out). Smoke started coming from the passenger footwell and I've melted some wires.
The melted wires come from the negative battery terminal and are spliced into two black wires of the loom immediately after the ECU. The loom looks like it might be ok but I guess the spliced in section was an inferior grade of wire. I assume this will be wiring for the alarm since it looks like an after-thought. I'll post some pictures later as I'm at work right now.
I've now checked the battery and it was reasonably fully charged.
I'm not sure what the cause is but I would guess it's an earth that isn't working properly (maybe the new chassis powdercoat is insulating it).
If the engine was too stiff for the starter to turn over; could that cause this effect or would the starter just not turn it over? Not sure why this would be but this was my first full engine rebuild.
Anyone any thoughts of the likely cause? What should be the normal path for electricity to return from the starter to the negative battery terminal?
Cheers,
Simon (feeling somewhat deflated)
Hedgehopper said:
Have you got a battery master switch? If you have and its turned off then your starter will try to use the two black wires you mention as an earth path....and will get very hot.
I don't think I have a battery master switch - at least I don't have one of the big obvious aftermarket ones sat on the terminal or in the footwell anywhere. I presume there isn't a factory switch hidden somewhere...Now I've more calmly assessed the damage things don't look as terrible as I thought.
This is the starter motor wiring which I'm assuming is correct. The thick red cable (hidden by the chassis) is attached to the same terminal as the many brown wires.
This is the start of the disaster zone where the two black wires are attached to the negative battery terminal.
Thankfully all the melted wire is in the footwell and doesn't continue far into the main body of the loom. In this shot the ECU is just out of frame to the left. Two thin black (undamaged) wires come out of the ECU and have the two melted wires from the negative terminal spliced into them. Then there's a short melted section before the two wires join into one thicker (undamaged) cable that disappears off into the loom.
Does this shed any more light on the cause? I don't know what this wiring is for but it looks like an amateur addition.
Am I still looking at the engine earth strap as the cause? I can't really see anything to suggest it wouldn't be fine.
spend - what fuse should go into these cables?
This is the starter motor wiring which I'm assuming is correct. The thick red cable (hidden by the chassis) is attached to the same terminal as the many brown wires.
This is the start of the disaster zone where the two black wires are attached to the negative battery terminal.
Thankfully all the melted wire is in the footwell and doesn't continue far into the main body of the loom. In this shot the ECU is just out of frame to the left. Two thin black (undamaged) wires come out of the ECU and have the two melted wires from the negative terminal spliced into them. Then there's a short melted section before the two wires join into one thicker (undamaged) cable that disappears off into the loom.
Does this shed any more light on the cause? I don't know what this wiring is for but it looks like an amateur addition.
Am I still looking at the engine earth strap as the cause? I can't really see anything to suggest it wouldn't be fine.
spend - what fuse should go into these cables?
Just to provide a happy update; the car is now electrically fine and started first time (for the first time in nine months).
Massive thanks to Shane Cooper at Motosparkz for coming over to replace the wiring and run some diagnostics.
It seems it was the new powdercoat on the chassis which had coated the insides of the engine mounts as well as the outsides. On a pre-cat, the OS engine mount is where the main engine earth goes to. Having cleaned that up and replaced the melted wiring, all was well with the electrics and she's suffered no other side effects. Just a few more little bits to tidy up over the bank holiday weekend and we should be good for our MOT on Tuesday.
Thanks for all your replys as always, they were very helpful. I've now got two big earth straps going directly from block to chassis. It's overkill I know but as LongBaz said, the car has never cranked over as fast as it does now.
Cheers,
Simon
Massive thanks to Shane Cooper at Motosparkz for coming over to replace the wiring and run some diagnostics.
It seems it was the new powdercoat on the chassis which had coated the insides of the engine mounts as well as the outsides. On a pre-cat, the OS engine mount is where the main engine earth goes to. Having cleaned that up and replaced the melted wiring, all was well with the electrics and she's suffered no other side effects. Just a few more little bits to tidy up over the bank holiday weekend and we should be good for our MOT on Tuesday.
Thanks for all your replys as always, they were very helpful. I've now got two big earth straps going directly from block to chassis. It's overkill I know but as LongBaz said, the car has never cranked over as fast as it does now.
Cheers,
Simon
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