Yoda

Some years ago we had the fuel tank out of our 85 EFI pickup. When we reinstalled the tank, we inadvertantly crossed the vent and the fuel return lines at the tank (no labels on hoses).
A few days later, we had fuel coming out of the charcoal canister. This was because the vent tube goes to the top inside the fuel tank, and the return goes to the bottom inside the fuel tank. The tank pressurizes when sitting in hot sun, gas expands, and because the vent hose was connected to the return tube on the tank, the gas was forced out to the canister.

Easy fix, we thought, just swap hoses at the frame rail. It no longer dumped fuel out the canister, but started running rich. We adjusted the AFM screw so it would run better at idle, but it still wasn't great.

So, after a couple years like this, I checked the fuel pressure (hell to find an adapter for the cold start valve). Spec is 33-38 PSI with vac line dis-connected, and 27-31 psi with vac line connected. It was running at 53 PSI either way. Bad regulator? I swapped another I had, and it was the same. I pinched offg the return line and it jumped up to 65 PSI, so something was geting back to the tank.

I disconnected the return hose off the regulator, and ran the hose to a bottle (giving me a simulated return line to tank). The fuel pressures were PERFECT!

So yesterday, we pulled the tank to check for pinched lines above the tank. Found the return line (that used to be the vent line) had a restriction in it. Cut open the line and found a small screen restrictor inside the hose. OEM. The screen I believe is to prevend liquid fron getting to the canister. So I bought 2 new hoses, inserted the screen into the vent hose, marked the hoses with paint to identify them correctly and re-installed the tank.

The pressures are perfect now with the truck running. Just have to dial the AFM mix back to what it was

Should get better than 17 MPG now.

Moral of the story is to fix it right as soon as you realize there is a problem

aquamato

words to live by

Elton