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Fiat 125p voltage spikes (project car)

  • abdelmonaim
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26 May 2019 13:13 #30116 by abdelmonaim
Fiat 125p voltage spikes (project car) was created by abdelmonaim
I've a 1973 fiat 125p, current setup is basic carburetor/distributor engine. Ignition circuit was contact breaker with capacitor, but now it utilizes a transistorized ignition (velleman Kit K2543), car runs fine but I'm about to convert it to efi (hopefully it will run some day on efi :D), before I started the conversion I decided to make some tests, that is when I realized the voltage spikes problem. Firstly I suspected the alternator as the multi meter read fluctuation more than 19V on battery (min 13v, max "have no means to measure it") anyway changed the voltage regulator and same behavior, removed the alternator and tested it on bench using car battery as load and electric motor @ 1725 RPM alternator was outputting 14.5v steady no matter the loads on it(was occasionally connecting radiator fan and head light lamps as loads), so I ruled out the alternator.
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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26 May 2019 13:41 - 26 May 2019 13:43 #30118 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Fiat 125p voltage spikes (project car)
FSO Polski 125p ? While you could try putting a rectifier diode in power feed to your coil and I hate to pour cold water on what you have done so far. but just bin the Vellman kit. Transistor assisted points ignition systems were never that successful and alsoretained all the disadvantages of points ignition.
There some budget price points free ignition kits available for Italian FIATs not sure about the FSO.

"There's always a catch ---- Catch OBD2 ."


Last edit: 26 May 2019 13:43 by Andy.MacFadyen.

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26 May 2019 13:50 #30119 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
I was actually just thinking of removing the velleman kit, and use just old plain contact breakers and capacitor, and monitor the difference, after all I just need stable voltage to start the conversion which will hopefully include COP at some point. will check with old configuration tomorrow and see what happens. thanks for the reply

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26 May 2019 14:25 #30121 by guafa
Replied by guafa on topic Fiat 125p voltage spikes (project car)
Hi guys,

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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27 May 2019 01:20 #30144 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Fiat 125p voltage spikes (project car)
If you are serious about going to fuel injection then a Megasquirt kit is the way to go it covers both injection and ignition. Normally rather than COP a Ford Zetec 4 cylinder wasted spark coil pack is used.

"There's always a catch ---- Catch OBD2 ."


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27 May 2019 04:15 #30148 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
I chose another open source ECU, which I find promising and is being constantly updated, Speeduino.
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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27 May 2019 07:59 #30150 by guafa
Replied by guafa on topic Fiat 125p voltage spikes (project car)
Speeduino uses atmega processor, which experts say is not as good as other brands for industrial enviroments, then are not well protected for electromagnetic noises. I can't talk about other processor, since is the only one i have used in car projects.

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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27 May 2019 15:45 #30158 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
Removed the transistorized kit, and ran with the default configuration of contact breaker and cap, I even completely discontented the alternator, and connected the coil power directly to the battery to eliminate any suspicion in the wiring harness and this was the result

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27 May 2019 18:05 #30159 by guafa
Replied by guafa on topic Fiat 125p voltage spikes (project car)
Try with internal resistance spark plugs.

Look for the ones with same thermal grade and same size.

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28 May 2019 10:51 #30176 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
will search for compatible spark plug.
some suspect that its a rotor/distributor cap problem, what do you think?

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29 May 2019 00:52 - 29 May 2019 01:02 #30203 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Fiat 125p voltage spikes (project car)
Multimeters are not very good for that kind of job it really requires an oscilloscope scope But that looks like it needs a new condensor (capacitor) in the distributor to quench the spike at the points.
All ignition condensors are much the same.
0.22mf. high voltage rated type i.e. over 400v

"There's always a catch ---- Catch OBD2 ."


Last edit: 29 May 2019 01:02 by Andy.MacFadyen.

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29 May 2019 05:27 #30207 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
I already installed new capacitor in order to remove the velleman kit

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02 Jun 2019 14:59 #30329 by abdelmonaim
Replied by abdelmonaim on topic Fiat 125p voltage spikes (project car)
update:
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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02 Jun 2019 17:07 #30336 by guafa
Replied by guafa on topic Fiat 125p voltage spikes (project car)
Nice to hear that.

I think what you are seeing now, is a non good voltage regulation (not spikes frying your voltmeter).

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02 Jun 2019 17:29 #30338 by guafa
Replied by guafa on topic Fiat 125p voltage spikes (project car)
What do you mean with alternator offline?

You are having 15 volts, from where?

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15 Jun 2019 15:10 #30696 by SignalSimon
Replied by SignalSimon on topic Fiat 125p voltage spikes (project car)
Just a thought.... Does this setup originally have a ballast resistor ( whether a discrete resistor, or resistance wire in the harness) with the extra contact on the starter solenoid to bypass it whilst cranking?

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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