Fiat 125p voltage spikes (project car)
- abdelmonaim
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Now I pretty sure that the spikes originating from the ignition coil, the I installed a varistor on the power connection of the coil and the result was @ idle the fluctuation is between 14v to 18.5v, and when increasing RPM fluctuation/spikes insanely increases , tried changing the ignition coil with brand new one and still facing the same issue.
any idea what is wrong with my ignition circuit and how to eliminate or suppress these spikes, I fear that once I connect my ECU and try start the engine these spikes will fry the ECU!!
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- Andy.MacFadyen
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There some budget price points free ignition kits available for Italian FIATs not sure about the FSO.
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- abdelmonaim
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I have done this technical updates before (actually three cars 98 tbi renault 19 replaced with a Renault clio 1.2 siemens / 85 mazda 323 replaced with a Renault Clio 1.2 / 54 pontiac with a sniper efi system).
I spent months to realize why electronic circuit didn't work as i was expecting. Studying transient issues, grounds, power sources. All of my updates in circuit worked somehow, but what made the big diference was replacing spark plugs.
Original spark plugs for carburetor car are like a short circuit (i mean it does not have any resistance). Fuel injection spark plugs have more than 4 kohms instead.
This suppresed transient voltage spikes coming from spark plugs and avoid them to return to power sources.
I hope it helps.
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- Andy.MacFadyen
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" We're trying to plug a hole in the universe, what are you doing ?. "
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- abdelmonaim
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And I aim for sequential rather than wasted spark, though I can't find any noticeable benefit in doing so, but as long as the ECU supports it and I can do it, then I'm going to give it a shot.
Thanks for the input, will try to remove the velleman kit today after work and keep you posted about the results.
P.S: any directives about my build regarding wiring harness or any other aspect (as I'm going to build one from scratch) are highly appreciated.
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About wiring hardness, take special care to separate sensor grounds from power grounds. If ecu is well designed, internal ground paths are also separated, so you can leave sensor ground wire isolated even to battery lead.
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- abdelmonaim
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Look for the ones with same thermal grade and same size.
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- abdelmonaim
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some suspect that its a rotor/distributor cap problem, what do you think?
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- Andy.MacFadyen
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All ignition condensors are much the same.
0.22mf. high voltage rated type i.e. over 400v
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- abdelmonaim
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- abdelmonaim
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tested with internal ceramic 5K ohm resistance NGK spark plug, and there was a huge improvement.
but still reading is still a bit high(again alternator is completely offline)
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I think what you are seeing now, is a non good voltage regulation (not spikes frying your voltmeter).
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You are having 15 volts, from where?
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- SignalSimon
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That would show fluctuating voltage at coil positive but not at the battery.
If you're measuring directly at the battery terminals, there's no way you can really get those spikes if the battery is in good enough condition to crank the engine.
There is a reason for them being picked up by the meter, and that may be in the form of a radio signal.
Others have suggested resistive spark plugs and/or leads - this is their exact purpose.
Have you got an AM radio to hand? If each ignition event caused a loud crackle on the radio, there's your problem.
If it was one out of 4, you have an open plug wire!
Similarly the meter should be immune to radio frequencies but even Fluke get it wrong sometimes.l
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