Fuel leak? Can someone explain an efi fuel tank to me?


Founding Member
Jun 17, 2000
Linthicum, MD
I recently noticed a fuel leak while running my car. The leak is coming from somewhere in the fuel pump area. I dropped the tank today to explore but I could not narrow down where it is originating from. The entire top of the fuel pump area was soaked. Lines were dry and tight. The only obvious thing I noticed was a little bit of a dent around the edge of fuel pump holder assembly. Not sure if that is my culprit. By the time I discovered that i had already spilled fresh gas on the top of the tank. For that to be the culprit there would have to be a good amount of pressure in the tank since there is barely any fuel in the tank.

How much pressure does buid in the tank? And does it stay constant or only happen under acceleration? Thxs
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SN Certified Technician
Mar 10, 2000
Dublin GA
The likelihood of having a leak either from the fuel pump or tank sender access covers is much higher than a problem with the tank vent system. There is a rubber O ring in each of the access covers that will leak, along with the fuel tank filler grommet.

Fuel pressure in the tank is the result of the liquid gasoline vaporizing and creating pressure. It is managed by the Evaporative Emission Control system, AKA the carbon canister and canister vent solenoid.

The code 85 description explains how it operates.

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. This reduces the tank pressure.

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

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.

Purge valve solenoid:

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


Founding Member
Jun 17, 2000
Linthicum, MD
Thxs for the info!
My leak is definetly near the fuel pump. I was expecting it to be something obvious but of course its not. So you are saying there is enough pressure in the tank to leak fuel out of the fuel pump access cover? That is the only area I saw an issue with in that there was a small bend in the fuel pump holder mounting surface. Very small! Other than that I was suspecting the o-rings on the fuel lines themselves which are covered by the plastic ends. Thxs again. Very imformative... As always
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