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Rough idle, no-start, wait several hours, runs no problem

1999, Police Interceptor…
As the fuel amount decreases past a half-tank, it runs progressively more rough, harder to start, until it will not start.

After several hours, it starts no problem. Repeat, again. Fuel. Runs no problem.

Before it will not start at alo, it knocks and is like it is not getting gas.

Trusted Mechanic cannot determine the cause.

What has trusted mechanic done to troubleshoot this?

Have you verified fuel pressure when the car won’t start?

How long have you had this car? Is this a recent purchase? or had it for a while and this issue just started?
These vehicles had a history of exploding upon rear end collision, any chance anyone has modified the tank in any way to prevent this?

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I don’t remember the Crown Victoria having that exploding problem . Pinto’s did have that reputation.

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When it starts running poorly, if you open the gas cap, do you hear air being sucked into the gas tank?

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I must admit @lion9car makes a very reasonable and rational mention of what a non venting gas cap could induce symptomatically.

Has anyone done any fuel pressure tests ? Anyone verified the actual fuel level in the tank regardless of indicated on the dash?

I would do the simple test of the removing the gas cap as a very quick test to see if its a tank venting problem…very easy and will then steer diagnostics onto the next most logical suspect… and in my mind that would be the fuel pump (pump motor getting tired), fuel sending unit (fuel level) and or fuel pump pickup tube…or something along those lines.

Since this issue is repeatable…it should be rather easy to diag and repair.

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“Basically, the Crown Vic is a big Pinto.”
https://www.autosafety.org/popular-police-cars-crown-victorias-prone-explode-tied-deaths/

https://www.alexanderlaw.com/defective-gas-tanks-in-1992-2001-crown-victoria-mercury-and-lincoln-town-cars

Exploding Crown Vic- Youtube

Opened the gas cap when it was idling and the gastank was at 1/4, and no notice of air flow. It did have more of a rough idle.