1979-1993 & 94 Conv [Subscribe to Daily Digest] |
I've had this problem.
Forgive me if I point out the obvious. BTW, after writing all this, I thought…how old is your fuel filter? If it’s over two years old, replace it so you are SURE it’s not part of the problem.
EFP = main, high pressure fuel pump
The fuel pump is located in the top of the fuel tank in a plastic canister. As you are aware, there is a small pump that you refer to as a pre-pump that feeds the Engine fuel pump, the EFP. This pre-pump draws fuel from the bottom of the tank and fills the plastic canister, and then the EFP (which is submerged in the fuel in the plastic canister) draws from the canister and feeds the engine. The output of the pre-pump is not connected directly to the EFP.
The EFP sends high pressure fuel to the Fuel injector Rail, where the injectors draw the fuel required by the engine. Excess fuel, not required by the injectors, is returned to the fuel tank. This is important to understand. The excess fuel return line goes back to the tank, and inside the tank a rubber hose returns the fuel back to the canister that contains the EFP.
I’ve taken out fuel pumps and found this hose that returns fuel to the canister dissolved from additives to gasoline, perhaps alcohol. As a result the fuel is not returned to the canister but instead is dumped into the tank. This is a problem because the EFP is much more powerful then the pre-pump, so the EFP empties the canister faster then the pre-pump can fill it up. As a result, the canister is not kept full of fuel as was intended by the system designers. An important function of the fuel in the canister is to COOL the EFP.
When your tank is full the canister is kept full because it is submerged in the fuel. When the tank is less then ½ full the canister is not kept full, then EFP gets hot and possibly loses fuel pressure.
Poor performance, though, may be a sign that the fuel pump is about to fail. It’s failure may have been hastened by overheating as a result of what I’ve discussed.
You might remove the fuel pump and see if the return line is in good condition or not. If it has dissolved, try replacing it and see if that solved the problem. If not, you are probably looking at a new fuel pump. The obvious should be pointed out here. If you can test the fuel pressure, you should. That will tell you if you are about to lose the fuel pump.
Hope this helps.
posted by 128.125.227...
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