Perfect cold start and flawless running. But hot restart almost impossible

[Don]

I'm frustrated as can be with this. My `77 starts flawlessly when cold. Even after 5 months of storage. And then it runs flawlessly as well. Never stalls. But turn it off and wait five minutes and she simply WILL NOT restart.

I've had mechanics look at it. None has found the answer.

Some have suggested it not a fuel or electrical issue but one caused by a buildup of crankcase pressure -- the type that on US cars is corrected with a new PCV valve.

Anyone has any well founded ideas? Is there such a valve on a `77 Spider?

-Don

[18Fiatsandcounting]

Don, I doubt it is a crankcase pressure issue as that would be happening when the car was running as well, and besides, it's hard to see how the crankcase would build up pressure when it's just sitting there after you turn it off.

A couple ideas:

1) Does your car have the dual point ignition? If so, it may be that the cold start points are working fine, and the hot points are set not quite right so that it will run once it's started but won't start when the engine is still hot.

2) Try this: Run the car as you have, turn it off, let it sit for 5 minutes, and then try to start again, but this time hold the gas pedal all the way to the floor when cranking. Don't pump it, just hold it fully down. I have seen some cars that "flooded" after being shut off in a hot condition, as there was too much gas in the intake manifold. Eventually, this gas evaporates (can take hours or days) and then it starts again. If your car eventually starts when holding the pedal to the floor, let us know and we can figure out why you have too much gas getting into the engine. Note that it may take 10-20 seconds of holding the pedal down while cranking to clear the excess gas, so give your starter motor and battery a break every few seconds.

-Bryan

[bobplyler]

When it won't restart, does it crank?

[kilrwail]

This is going to sound odd, but do you have one of those green knobs on your battery's negative terminal, to act as a quick disconnect? If you do, GET RID OF IT! It can cause exactly the problem you've described because the quality of the ground connection is not good enough, especially when hot. With that in mind, even if you don't have a green knob, clean both battery terminals and cable connectors thoroughly.

[GeorgeT]

Vapor lock?

[TX82FIAT]

Check ignition magnetic pickup coil. As I understand it the ignition coil can overheat causing a non start when car is warm and start when car/coil is cold.

[kilrwail]

How close is your distributor trigger wire to your exhaust header (the small wire between the distributor and coil)? If that wire gets too hot, the car won't start until it's cooled off for a while. Try to relocate it so it's not near the header.

[RRoller123]

undo the gas cap when this happens and listen carefully for any rush of air in.

[Don]

I appreciate the thoughts and comments.

I will definitely check the positioning of the coil cable. The coil and wires were replaced roughly about when this problem started.

The fuel cap has a very small hole drilled in it some 30 years ago to prevent that issue. I checked the hole and it is still clear.

Vapor lock was my first guess. My understanding is that the electric fuel pump and fuel return system makes such unlikely in carbed Fiats such as mine, and the fuel system was gone over, hoses replaced and a fuel pressure device was installed for frankly I do not know exactly what reason. Is there a simple way to check this?

The car was originally a two pointer. It was changed over to a single point setup set some years ago.

No, there is no such battery turn off. And what's more I have installed a direct run (thru a switch) from the battery to the fuel pump -- that completely rectified the occasional cold starting issues the car used to have. (I could tell that the fuel pump was not running by the lack of sound -- after the engine caught it would come on. Now I turn it on manually when it does not come on itself. Once running, again, it runs flawlessly. I turn the switch off.)

And yes it cranks. Strongly.

-Don

[18Fiatsandcounting]

Thanks for the extra info. Vapor lock usually occurs when driving, but you could have a "hot soak" issue somewhere, so when the engine is shut off and just stewing in its own hot juices, something either ignition or fuel related doesn't work until it cools down again. Try this: Get the car hot, park it in the shade, turn it off, open the hood, and maybe put a house fan blowing over the top. Try to start it after a few minutes and see if the issue is any better.

-Bryan

[seabeelt]

Did this ever get resolved? Does the car have a ballast resistor? I had a similar issue ( exactly the same description). Ballast resistor crapped out if the car ran a while and then was shut off. It never stopped running mid stream but just wouldn’t start when hot ( full engine bay temp). Swapped it out and it has run fine ever since

[18Fiatsandcounting]

I'll let Don answer the question on whether this was resolved, but just a comment on the ballast resistor. Many resistors increase in resistance with age and with temperature. So, if the ignition system was a little on the weak side, those two factors might push the ballast resistor over the edge in terms of not giving you a hot enough spark to start the car. Might work well enough when cold or when already running, but many older engines need a little extra "kick" on the spark to get them started.

-Bryan

[ShantzBoyz]

I want to thank everyone on this forum. It has helped me solve several issues on my ‘78. I was having the same issue with not starting when hot. Based on information on this forum, I took a multi pronged approach. I swapped out the no-name ignition coil for a Marelli from Vick’s, increased the size of the wire running from the distributor to the coil to reduce resistance, relocated that same wire to run as far as possible from the exhaust manifold, and fabricated a heat shield for the coil. Voilá! It now starts without hesitation regardless of temperature.

[PeterParker]

+1 on ballast resistor. Had the same problem. Drove me nuts. Overheated coil can cause the car to backfire and stall at speed but restart when it cools down.