Fuel System Help

Revogen

Active Member
May 10, 2016
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OK. So, 1987 Mustang GT. I put in a new tank, fuel pump, sending unit, etc. including new grommets and vapor valve, put some fuel in, fired right up no problems. Drove the car (over a few weeks) about 60-70 miles no issues. Last week I go to the gas station, put some gas in (Tank is fairly full after but I did not fill to the point where the pump shuts off), heading home and find out it's puking gas out the back end. I put up on the jack stands and drop the tank (ugh) and the only thing I find wrong is the vapor valve is not fully seated in its grommet and it's clear that this is where the gas had spewed from. My initial thought was that I'm a dumb-ass and didn't fully seat the valve when putting the new tank set up together so I clean everything up, push the valve fully into the grommet, put the whole shebang back together, fires up fine. I let it idle for 20 minutes while I check for leaks, no problems, not a drop. I take it out for a ride around the block, pull back into the driveway and puking gas again.
I suspect there is something wrong downstream of the vapor valve. Could there be a blockage or something that is backing up pressure in the tank and then blowing that vapor valve out of its grommet and hence allowing fuel the spew out???
I do not have an adjustable FPR, nor have I checked the pressure yet (need to rent a tester later this week) although I'm concerned I won't get a proper reading until I drop the tank again and reinstall the vapor valve completely.
And again, this is a brand new tank, new sending unit, new 255LPH BBK fuel pump, new vapor valve & grommet.
Any help would be appreciated. It will likely be a few days before I can drop the tank again...
 
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I am wondering if anyone knows, if the purge valve solenoid fails to open while under acceleration, will the resulting (trapped?) vapors create enough pressure in the tank to blow out the tank vapor valve? Either there is somehow too much pressure building in the tank or the vapor valve/grommet are not sized correctly for the tank???
 
Is the carbon canister and carbon canister purge valve still present and working? They are often victims of the previous owner's ignorant efforts to make the car faster by removing the emissions equipment.

Code 85 CANP solenoid - The Carbon Canister solenoid is inoperative or missing.

Revised 11 –Jan_2015 to add warning about vacuum leaks due to deteriorated hose or missing caps on vacuum lines when the solenoid is removed.

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.

If you disconnected the carbon canister and failed to properly cap the vacuum line coming from under the upper intake manifold, you will have problems. You will also have problems if the remaining hose coming from under the upper intake manifold or caps for the vacuum line are sucking air.

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.

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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:
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The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:
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