Technical Pulsating lights & dash - 500 1.2 Pop

[Crashedfiesta]

Would you believe I haven't posted here since 2009, that's how reliable our 500 has been!

But we had a few issues recently with the head gasket that meant it had to go for some significant repairs. Won't go into details but the repairs sort of snowballed so we've got quite a bit invested in it now.

Anyway, the engine is now ticking along as if it's new and the sound is glorious compared to how it was before (I did just notice Fiat still insist on that ridiculous plastic screw on the heater pipe - really Fiat?) but now we have a new problem.

With the engine running the lights pulsate, and so does the dashboard. It gets slightly less noticeable when at higher revs but there's a definite flickering to everything that also affects the running e.g. downhill with the clutch out in 3rd or 4th there's a real jerkiness to the ride.

I've tested the battery and at rest it puts out 12.4v and with the engine running it measures 14.7. I've checked the various ground straps that I can reach as well as other random points across the body and the voltage stays pretty consistent around 12.4 or 14.6 depending on if the engine is running. So I'm thinking it's not a bad ground.

I am thinking that it's most likely the alternator that's starting to fail. Would any of the techies here agree with that or have any other suggestions? If I can I'll try and catch a quick video (if the forum will let me upload it!).

Cheers,

Crashed.

 

[GettinBetter]

... downhill with the clutch out in 3rd or 4th there's a real jerkiness to the ride....

Roughly at what RPM? Can't say I've ever heard or experienced that before. I only get that when I forget to push the clutch in occassionally (the wifes car is an auto, and so is the works truck).

I am thinking that it's most likely the alternator that's starting to fail. Would any of the techies here agree with that or have any other suggestions?

I would initially agree, the alternator is three phase AC, and has three diodes to allow the positive part of the cycle to flow (via a voltage regulator) to the battery. If one of the diodes goes OC, it would be seen as pulsing, as for each revolution of the alternator, the output is only two of the three pulses.

12.4V is not a fully charged battery, or is a battery voltage that is beginning to suffer from a faulty alternator, which maybe why you can actually see the pulses.

I've tested the battery and at rest it puts out 12.4v and with the engine running it measures 14.7. I've checked the various ground straps that I can reach as well as other random points across the body and the voltage stays pretty consistent around 12.4 or 14.6 depending on if the engine is running. So I'm thinking it's not a bad ground.

This NOT a reliable ground test. Add a good quality jump lead from the neg terminal to a clean (easily accessible) part of the engine to compare any of your tests. Using a DVM may show continuity , but to get that reading, it only passes a very small current through the earth path, if the circuit is compromised, it can usually pass that very small current, but not heavier loads without a voltage drop which will show up as a fault. Sorry, if you all ready know that.