re: ECU fuse blowing

[Paul_Hedley]

Having done some reasonable surfing round on these pages and finding ECU fuse blowing topics, it seems that although the symptom is the same, the cause may well not be in this case.

 

I recently had a Battery master switch fitted, which has been very useful as my garage has no power. When I came to the car on Wednesday night, and enabled the switch, I then had no fuel pump etc - traced to a blown ECU fuse. Duly replaced, all seemed well. The following morning, same drill, same result: blown ECU fuse. Everything seems to be running fine once the fuse is replaced. I tried swapping the fuse for a 30A this afternoon, but that blows in exactly the same way. Clearly something not right.

 

Is this likely to be an earthing issue, and if so, where should I start to look? I took the knee panel off this afternoon to check the connections on the BMS, which all look fine, except that the earth to the chassis looks a bit corroded (slight concern since switch was only fitted 2 1/2 months ago). I'll clean this up tomorrow. Is this 'channel' behind the knee panel a known water trap? Given that there seems to be a gap in the panels straight out to the edge of the bonnet, I might fill this up, though not sure what with.

 

Any pointers from you experienced electronics gurus would be much appreciated.

 

Many thanks

 

Paul

[The Outcast]

edited to prevent confusion I should have said a loose earth can cause arcing and blow a fuse [From experience]

 

Edited by - The Outcast on 12 Mar 2010 22:57:18

[Ian B]

Unlikely to be poor earth connection. Poor earth would lead to increased resistance and decrease in current.

 

It is generally accepted that the 20a ECU fuse should be changed to 30a for reliability, however if that is going as well, then there is something else wrong.

Could be a positive feed cable (on the ECU supplied circuit) chaffing through the insulation to earth??

 

---

Ian - Slightly Vider SVelte SuperVeloce model 😬 - Joint AR for North Kent - Area details and calendar here

[Paul_Hedley]

Thanks for the ideas.

 

Ian - is there an easy way to identify the positive feed cable (colour?) so that I can check it? My initial assumption was it was likely to relate to some sort of earthing, but my cursory inspection this afternoon didn't yield anything obvious.

 

Thanks

 

Paul

[The Outcast]

Which model what year???

[Paul_Hedley]

97 1600 supersport (K series).

[Paul_Hedley]

I have been thinking about whether anything else had changed between all being well and not well. The only thing I can think of is that the car was washed. Might this be a water related problem?

 

Thanks for everyone's help.

 

Paul

[Paul Deslandes]

water doubtful cause. From your original description it sounds as though the problem correlates with the FIA switch installation. Is the cut-out switch mounted on the driver's side of the scuttle in usual place and do you have the knee panels fitted? If so, the panel can get very close to the battery cable terminals on the switch and short out. This may be happening when you turn the switch off as it twists or the scuttle panel flexes slightly.

 

You could try removing the knee panel and seeing if the problem reoccurs and you might even see a witness mark from any arcing that's have gone on. You can just stick some insulation material to the inside of the panel or over the exposed terminals and/or, as I did, beat a dish shape into the panel so it clears the terminals.

 

Paul

 

 

[Paul_Hedley]

Paul,

 

Interesting suggestion - I'll go back and try that. Having done some tracing of wires, I can't see any evidence of the problem elsewhere, and the fact that everything seems to run as it should, and that once the BMS is on, I can put a fuse in a it doesn't blow, does seem to point towards the switch.

 

I suppose it's also possible that the switch itself is faulty.

 

Many thanks

 

Paul

[Paul Deslandes]

Yes it could be the switch or it might have been installed incorrectly although I think this would have shown up straight away. There is a resistor, which is white and about 5cm long and 8mm square with two wires coming, either one out of each end or two from one end, depending on type used. It should be secured in a clip and is connected between one of the four smaller switch terminals and chassis and is switched into circuit when the switch is turned to off. It would be worth checking that the wire between the resistor and the switch isn't touching the chassis somewhere.

 

Paul

 

 

[Paul_Hedley]

The plot thickens.

 

After further investigation earlier on, I thought I had solved it as after cleaning the slightly corroded earth contact and trying to operate the switch without the knee panel, the fuse didn't blow. Power, engine start - all fine. Until 90 secs later when the engine died, as it turns out as a result of a blown ECU fuse. I've never had it blow while running before. A replacement fuse, with BMS still enabled, and all is well again - engine running happily for a while.

 

However, on turning off the BMS, ECU fuse blows again, and this time replacement with BMS enabled also blows.

 

Not sure what else to try here, short of phoning CC to ask for a replacement switch.

 

Paul

[Paul Deslandes]

Hmm. It does sound like the switch is the most likely cause of the problem. One other possibility is the wiring behind the ignition switch. This was 'interfered with' when the FIA switch was fitted so it might be worth just checking the white wires where they've been taken off the switch terminals. For details of the wiring have a look here. If this doesn't show anything obvious you could try reinstating the original wiring connections, or just get a new switch.

 

 

[The Outcast]

Have you carefully checked the wiring on the BMS I refer to the Resistor wiring for the Alternator NOT the main Cables Just an idea because it is a very uncommon fault