Engine stops for no apparent reason

[charlielucky]

Hi, My Fiat 124 2000 restoration project is complete and the car has passed the French technical check and is now registered here in France as a vintage vehicle. The problem I have it that sometimes for no apparent reason the car won't start, and sometimes while running the engine just cuts out. If I leave the car for a few hours it will start again!

I have a new fuel tank, fuel filter and pump, and new original Bosch injectors. I have a good spark and there is no air leak along the injector intake. I'm racking my brains trying to work out what could be wrong. I'm wondering if the culprit could be the fuel pressure regulator? If you have any suggestions of where to begin troubleshooting it will be much appreciated.
charlielucky

[TX82FIAT]

Does the car always start and run for a while when cold and then cut out when warm or when you go to re-start. If that is the case I would suspect the coil module is overheating

[charlielucky]

HI, thank you for your advice. My car is in a local garage for the moment to try and find the problem. Unfortunately here in France there are very few Mechanics that still work on 1980's. cars. I'll go and see him and ask him to check out the coil. Any other suggestions?

Kind regards

Charlielucky

[18Fiatsandcounting]

If the engine started sputtering or faltering before it cut out, then I might suspect a fuel issue. However, since the engine cuts out completely (without warning, I assume), that I think TX82FIAT's suggestion is the place I'd start, with the ignition control module or the coil itself.

One other possibility: Check the gap in the distributor between the 4-lobed rotor and its magnetic pickup. If that gap is too large, the lobes on the rotor won't trigger the sensor and you won't get a spark. I tend to set this just a little bit lower than what the spec is, and my recollection is that this is around 0.40mm.

-Bryan

[charlielucky]

Good morning,

Thanks for the additional advice. My local mechanic thinks there is a problem with the valve settings so he's going to check them on Monday.
The car doesn't splutter so I think the problem is electrical. I'll try and get the car back to my place and work through the your suggestions.

Thanks again

Charlielucky

[charlielucky]

HI, I spoke with my local mechanic again today and he said that when the car stops there is a strong smell of gasoline. He thinks it is possible that the car is flooding. Any idea what could be causing this?

Thanks again

Charlielucky

[charlielucky]

Hi again, I forgot to ask if it is normal for the fuel pump to only come on when the key is turned to the start position?

charlielucky

[18Fiatsandcounting]

Charlie, on a fuel injected car, it's pretty unusual to smell gas around the engine compartment unless one of the fuel or return lines has a leak. Usually on these cars, the smell comes from the gas tank area, and that is again often an old or leaking hose. There also can be an issue with the fuel vapor recovery system in that pressure builds up in the tank and gas (or vapors) forces its way out. You could try loosening the gas cap just a bit (one turn) and see if that helps if there is any pressure buildup.

As for when the electric fuel pump should turn on, it should come on when you turn the ignition key to "Run" (On), but before starting the engine. The pump should stay on when you turn the key to "Start" although you usually can't hear the pump running while the engine is cranking.

-Bryan

[spider2081]

Hi again, I forgot to ask if it is normal for the fuel pump to only come on when the key is turned to the start position?

This is one of the normal conditions for the fuel pump to run. The other is for the ignition key to be in the "run" position and the flap in the airflow meter to be opened. The key in the "run" position by itself will not power the fuel pump, air flow through the air flow meter moves the internal vane closing the fuel pump switch that powers the dual fuel injection dual relay that then powers the fuel pump. For faster engine starting the fuel pump is directly powered when the ignition key is in the start position.
Hope this helps

[charlielucky]

Hi everyone, I'm starting to loose hope of ever getting my fiat running on the road! I'll try and explain exactly what is happening when I start the car.

When the car is cold it generally starts first time and runs beautifully on idle revs. If I rev the car over 3000 rpm the engine starts to splutter as if it is only running on 2 cylinders and no amount of throttle will bring the engine back running normally. So I have to stop the car and it will sometimes start again and run normally at idle speed. Sometimes the car will not start at all. If I wait an hour or two the car will start again running smoothly up until 3000. rpm. I may be mistaken but it seems like there is a smell of gasoline in the engine compartment when the engine starts to splutter.

I haven't touched the distributor cap during the restoration. I'm wondering if there could be a problem with the vacuum unit on the distributor?

Any advice will be very much appreciated.

Charlie lucky

[18Fiatsandcounting]

Do you have a catalytic converter? These do get plugged up, as do the exhaust system in general sometimes, and this can cause the engine to not rev freely.

I would definitely check your ignition timing. It should be around 5 to 10 degrees BTDC when at idle (850 rpm) and then advance to about 35 degrees when the engine is revved to 3500 rpm or so. The vacuum advance can cause problems, but I don't think that is your issue.

You have fuel injection, right? If so, another thing to check would be the large rubber hose that goes from the air fuel monitor (AFM) to the inlet of the throttle body. For fuel injected cars, there should not be any air leaks.

-Bryan

[charlielucky]

Hi Bryan,

Thanks for the tips. My car is an 81 Bosch injected us model with a catalyser. I'll try and check the ignition timing and double check the air intake for leaks.

I'll let you know how I get on.

Charles

[charlielucky]

Hi Bryan,

Excuse my ignorance, but what does BTDC mean?

Charles

[18Fiatsandcounting]

Hi Charlie, BTDC stands for "Before Top Dead Center". Top Dead Center (TDC) in an engine refers to the position of the crankshaft where one (or more) of the pistons are at the very top of their stroke. On a Fiat engine, cylinders 1 and 4 are at TDC at the same time, while cylinders 2 and 3 will both reach TDC together as the crankshaft rotates another half turn. Other engines, such as straight sixes and V8s, will be different depending on how the piston timing is arranged.

BTDC is a timing term used to describe when the spark plug fires. The spark plug fires before the piston reaches the top of its stroke because the fuel takes a certain amount of time to start burning and reach full pressure. The faster the engine is spinning, the earlier you need to ignite the fuel with the spark plug, so the ignition timing "advances".

ATDC would refer to After TDC, but this doesn't apply much to ignition systems. There is also BDC (Bottom Dead Center), but that's not used very much.

BTDC, ATDC, BBDC, etc. are used when describing camshaft timing, which determines when the valves open and close.

-Bryan

[charlielucky]

Hi Bryan, thanks very much for the explanation. I've learnt a great deal during the restoration but I still have a long way to go....

Hope you have a good weekend

Charles