Car does not start when hot

[PAV1980Spider]

1980 Fiat 2000 FI starts normal when cold. Runs very well but....once it reaches 190 degree and I turn it off and wait for 20 minutes then it will not start again. Changed the CSI and the temp switch, new head gasket, net distributor cap, gas pump seems to have good pressure, although I have not measured. As I said runs well otherwise. The only thing I just found is that the gas line to the CSI weeps tiny amount of gas. I guess it does affect the gas pressure going into the injector. Does anyone think that this could be the culprit for the hot start issues?

[So Cal Mark]

if you lose pressure in the fuel rail, you will boil the fuel during a heat soak and make restarts extremely hard. The system should hold pressure at rest

[courtenay]

I had the same problem. Turned out it was the fuel pump. Worked fine when cold - not when hot. You can check it when the engine is hot and not starting by turning the key to the "on" position and manually moving the arm on the AFM to open it - if the fuel pump doesn't start, it's likely pooched.

[RRoller123]

if you lose pressure in the fuel rail, you will boil the fuel during a heat soak and make restarts extremely hard. The system should hold pressure at rest

Interesting... so mine is wired to have the pump on all the time the ignition is on. I always let it run for a few seconds before engaging the starter, to ensure the pressure is up, (and you can hear a very few air bubbles being immediately purged). It also now occurs to me that this would flush hot or vaporized fuel out of the rail, and replace it with cooler fresh fuel from the tank if you let it run for say 5 seconds or so before engaging the starter.

[So Cal Mark]

until the injectors start pulsing, air will still be in the rail. When you lose pressure at rest on a hot engine, the fuel in the rail can boil creating a vapor lock. If the pressure loss is caused by dripping injectors you also have a flooded condition in the cylinders

[RRoller123]

Would not the passing of cold fuel through the fuel rail manifold very quickly condense any vaporized fuel there? It would work in a thermal gradient (wave) from the rail towards the injectors, and I would estimate maybe within 10 seconds or so (wild guess) the existing fuel should be cooled and re-mixed with fresh?

[PAV1980Spider]

Thanks for the suggestions. I intend to follow through on all of them. Just fixed the fuel line to the CSI but this made no difference.
I forgot to mention a very interesting phenomena related to my hot start issue. If I crank the starter the engine will not start when hot even though the starter will be rotating the engine very well. At the same time, if I push the car and engage a gear, then the engine comes to life almost immediately. I have no idea how to explain this. What does (or does not) get engaged differently when the engine is cranked by the starter or rotated by the motion of the wheel? The only thing I can come up with is that when pushing the car the electricity coming from the battery does not have to feed the starter. Is it possible that the hot start is a battery issue (which in my case is quite old)?

[PAV1980Spider]

Almost certain that it is not the battery. Drove it a bit, enough to rise the temlreature to 190 and then tried to start it with jumper cables, attached to a running SUV. Did not make any difference. Back to square 1. Next will be the fuel pump replacement. Have the feeling that by the time I get this fixed 50% of the car may be new....perhaps a blessing in disguise.

[micbrody]

I have had the same problem intermittently. I did replace fuel pump (after testing and seeing it had issues maintaining high pressure in fuel rail. I think this helped; but never totally solved problem.
If you have been following any of my AFM threads, you can see I have tried fixing an old AFM; one thing I did notice was car starts better when I had copper swing arm moved to a virgin part of rheostat board. Not sure, but car stars better....including hot starts. One theory I am suggesting is that when car is warm, the AFM itself is warm; the copper contact arm slightly expands, and rests on an overused part of rheostst board near "idle" air flow. When starting car when hot, there is little fuel entering engine because: too hot for CSI to contribute; and the t -temp sender is showing car as hot, thus shortening injector open time; if AFM also shows high impedance (poor electrical contacts), the fuel mixture is also incorrectly matched to an excessively lean mixture.

So in summary: try rehabing AFM so contact arm swings along virgin reostat material

[GeorgeT]

Things that could cause this when a car is hot: a bad ignition coil, a bad ignition control module and a bad dual relay. These items heat up and can fail hot but work when cool.

[spider2081]

So in summary: try rehabing AFM so contact arm swings along virgin reostat material

A simple way to achieve this is remove the screws that hold the printed circuit board to the AFM elongate the holes in the board a bit and then move the board slightly so the wiper contacts a new area of the PC board, replace and tighten screws.

[spider2081]

Have the feeling that by the time I get this fixed 50% of the car may be new

Replacing parts with out any troubleshooting sure can be expensive and in some cases even introduce new problems. More than one post here have been of people replacing ignition control modules and distributor pick-ups that caused new issues. I think you might consider learning how to make some meaning full tests before replacing parts.

[PAV1980Spider]

Good point about the meaningful tests. I can't keep relying on gut feeling only, although I though that this was a big part of the fun of having a 40 years old Italian car.

Anyway, I did take a look at the AMF and it is true that the reostat material was worn off quite substantially at the beginning of the track.



I attempted to move the contact points to "virgin" material but it did not affect the hot start issue. It is possible that I did not do a good job adjusting them and that the "nipples" still rode on bad surfaces. At the same time, I did try to by-pass the worn off track with no positive results again. I will try to move the board now for better contact, as suggested; I suspect that there should be some "slack" in the board holes that will allow me to slightly move the assembly around without having to slot them.

[spider2081]

I remove the screws holding the connector on and remove the connector this makes working or removing the board fairly easy

[zachmac]

[quote="PAV1980Spider"] If I crank the starter the engine will not start when hot even though the starter will be rotating the engine very well. At the same time, if I push the car and engage a gear, then the engine comes to life almost immediately. I have no idea how to explain this. What does (or does not) get engaged differently when the engine is cranked by the starter or rotated by the motion of the wheel? quote]

This is not what everyone has had you chasing if the statement above is true. The only difference in what you describe is the path for current through the ignition switch. You are getting current to the coil and plugs when in the running position but not in the start position. When I get home tonight I'll research this and remember what is different but I am pretty sure you are looking at an electrical issue, most likely in the ignition switch and starting circuit.