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Sharp voltage spikes, what cause?


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Morning all. After many many hours of investigation work and testing, David at Canems ECU's suggested it may be the unusual sharp voltage spikes above and below a baseline of about 14.4v (up to 16.5v low as 12.5v) that could be upsetting the ECU and causing the un-tracable rich running and misfire. So, I disconnected the fan belt and ran the engine and now I still see voltage spikes but now only above a baseline of 12.5v obviously with the alternator not turning. 

Is the voltage reg still in circuit with alternator not turning? What else could cause such spikes? I expected to see a nice smooth voltage trace with the car running solely on a battery....

Chris.

 

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If you have just taken the belt off the wiring will be in the same state and still in circuit.

 

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High voltage cables ‘leaking’ to low voltage lines ??

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Hi Peter, perhaps..... I have tried to separate HT from LT but not much difference. Next up is to remove alternator and therefore the voltage reg from the equation entirely, then see what happens.

 

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  • 1 month later...

Good point, no I haven't although it does 'look' to be good, but an easy one to try. I'm planning some garage time soon and have several ideas to try out as well as this one.

Thanks, Chris.

 

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  • 1 month later...

I remember also reading somewhere (Pelican!) the earthing strap under the car (maybe the gearbox one) should be checked and cleaned as they has caused problems

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Thanks Chris, I did clean and change that along with many other earths and components and cables, all to zero affect. ECU now with Canems for a health check.

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