Fuel Stumbling After Long Highway Cruise

Discussion in 'Fox 5.0 Mustang Tech' started by boostfrk, May 14, 2013.

  1. So I drove my car across the Florida peninsula last week for work; about 2 hours each way. I made it there without issue, but on the way back I stopped for gas. I exited the highway, slowed, and downshifted to third. When I tried to let out on the clutch and rev match by giving it some gas nothing happened. I was going slow enough now that I just let out on the clutch and tried to accelerate, but nothing. The car never died, but stumbled pretty bad.

    I was able to roll into the gas station and shut the car off. I filled up, then the car started just fine and drove the remaining 30 minutes home without issue.

    I did a little bit of research and found a TSB for the newer Mustangs with a similar issue. Seems to be either the fuel filter needs changed or the fuel pump. I will swap out the fuel filter this week since it's easy and I have no idea how old it is. Obviously I don't want to drive another 2 hours just to see if this issue is fixed, but I'm getting ready to drive the car from FL to CO next month and I need to make sure it's reliable.

    Is there a way to check the fuel pump? Does this sound just like a fuel filter issue? Something else?
  2. Any other reason to suspect the pump like low pressure or noise? Dump the codes as the tfi module and pip sensor can cause heat trouble.
  3. Nothing abnormal coming from the fuel pump otherwise.

    Only codes I'm getting are for smog equipment since the PO removed the smog equipment from the car.
  4. Did the tank hiss when you loosened the cap?
  5. Hell I don't think it's done that in the year and a half I've owned the car. I have a new Motorcraft gas cap by the way also.
  6. Should the fox's with the charcoal vent canister ever hear a hiss from the tank (unless it is a Cobra?)
  7. No, they shouldn't, but they will if there's a vent problem or if the tank gets too hot...which they do on occasion
  8. Two things at work here:
    1.) Posible fuel heating by an excessively large fuel pump. A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off or presuurizes the fuel tank! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

    2.) Inoperative or improper tank vent system: look for a code 85 in the code dump
    Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
    The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

    Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.


    It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?

    The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

    The purge valve solenoid should be available at your local auto parts store.

    Purge valve solenoid:

    The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
    Carbon Canister:
  9. That was part joke - Rattle snakes rattle so a Cobra should hiss, right?
    (BOO! Bad joke!)