90 Mustang 5.0 Stalling after braking from long highway driving


My 1990 mustang 5.0 LX has a very consistent stalling problem when travelling long distance on the highway at a good speed. After 2 hours of driving highway speeds and then pulling off the highway, the car stalls after I brake or stop at a light. I don’t know why this seems braking related, but not sure. I then sit and crank the motor and it cranks for a bit and starts right up. I think it’s fuel, but now sure yet.

Here’s what I have done:

  1. Tune-up: plugs, wires, cap, rotor
  2. new fuel pressure regulator
  3. new fuel filter
  4. new fuel cap
  5. Checked for vacuum leaks (none found)

It seems to not happen when the gas tank is low, but I can’t swear to it.

I’m going to run a fuel pressure gauge to the futhel rail and see if I can catch the drop off of fuel pressure when it occurs. Also, I noticed that the gas cap does not hiss when I unscrew it at any point in time.

Any help is surely appreciated!

Thanks All!

Do you have a temp gauge? Is it running hot after highway driving?

I would suspect one of the following.
A vacuum leak. (check the PCV hoses underneath the intake manifold)
A problem with the Idle Air Control valve. (a common problem too)
Lastly, and not necessarily logical, this can also be caused by a flaky TFI ignition module. Those modules are known problems anyway and I’ve owned a few Fords in the past that would exhibit the symptom of stalling after a highway run with the cause being the module.

An EGR sticking open can also cause a problem like this but it’s less likely than the others.

I’ll take a shot. I traded my 98GT when it would start then stall then start then stall, all while cold. Turns out it was the plastic intake manifold Ford put on that year. Once hot it started and ran fine. Someone told me it cracked from me using hi-test gas. If it runs good while hot I’d try the manifold.

It’s possible this is a gas tank venting problem. If air isn’t coming in through the venting gadgets to fill the space at the top of the tank as the gas is used, it will create a vacuum that prevents the fuel pump from getting enough fuel to the engine. One thing you might try is when this happens, open the gas cap, let it sit a minute for air to get into the tank (press on that little flap if necessary), then try starting it up.

If that doesn’t fix it, the fuel pump might be on its last legs. A fuel pressure test will tell you. Before I invested a lot of time and money, I’d replace the fuel filter and the air filter if that hasn’t been done recently.

This is an automatic, correct?

Does it feel like the lock-up torque converter is not disengaging after a long highway drive? If I am correct, it will behave as though it were a manual transmission car and you pulled off the freeway and braked to a stop without depressing the clutch.

Go to the parts store and order a fuel cap specific to your vehicle. Make sure the clerk looks it up for accuracy. Try it, because your vehicle uses a pressurized fuel delivery system. Then test the fuel line pressure