Technical Car Shuts Off While Driving

[vasilGR]

Good Evening! For months now I have been facing the following problem without anyone being able to find a solution: the car (FIAT Punto mk1 facelift 1.2 16v 86HP) while it drives normally, suddenly lose revs and shuts off and then does not start for a long time. The starter sounds but doesn't start the engine, or if it does, it shuts off immediately or after a few steps. After half an hour to an hour it works normally. The problem occurs suddenly about one time per month (after 2-3000 km). Moreover, the car even when it doesn't turn off, it's not performing well, I feel it kind of weak sometimes like it's going to turn off. Ι feel like Ι have to press the gas a lot harder to get it to go away.

I have changed these months: RPM sensor, fuel pump, spark plugs, spark plugs wires, fuel filter, oil, air filter, a central fuse and a main green relay (which powers the fuel pump) from the fuse box and some dry wiring. About 30 faults come out in diagnostics, we reset them and they come back. The faults concern the rev sensor, brain, low voltage battery and other sensors.

Any idea what it could be? We still don't know if it's an electrical or mechanical problem.

 

[jackwhoo]

Main -ve wire?

 

[Torleif]

If the engine works properly when cold, I would suspect that a faulty ignition coil is overheating.

 

[blu73]

sounds like weak battery or earth fault... to get so many errors i'd believe the low voltage warnings, that alone can cause all the other errors so first thing to make sure is good. whats the voltage across the battery and how much does it drop with load on it, just turn ignition on first, then lights, rear screen heater, interior lights, radio, everything electric and measure battery voltage again, the voltage should only have dropped a tiny bit. If thats okay disconnect the crank sensor (to stop fuel and spark), measure voltage while the engine is cranking over - again will drop but should not drop much.

if battery is fine then its check alternator is charging consistent and checking/cleaning earths.

 

[vasilGR]

After a thorough inspection of the car, the mechanic although he didn't find anything specific, did a preventive cleaning of the map sensor and also made two small holes in the tank cap as he told me that if it doesn't get air, the fuel pump is forced and it can generate the problems that I used to have. What's your opinion? Have you ever heard it before?

 

[blu73]

tanks have breathers already, i guess its possible it could be blocked but drilling holes in the cap seems silly, will just vent fumes all the time and stink of fuel surely. I'd not do it to my car in a million years is my view.

Have you checked the battery, alternator and earths yet?

 

[vasilGR]

Thank you very much blu73. Yes, I have checked all of these in many car & electrical workshops. Nobody found anything. Τhe only thing they all came to is that maybe there is a problem with the ECU. Of course, as far as I know, the first generation of Fiat Punto (mk1) had no problems with the ECU.