fuel pressure prob or not

[thenn3025]

My problem is back with a vengence now. It was stalling when I pushed the clutch in and the engine idled down. Now it can't go 3 feet sometimes without the engine bogging down or dieing. Seems worse in reverse. Ok here's what I know. Engine is good internally. Been overhauled 2 years ago. Pulled compression test-OK. New plugs,wires, cap and rotor. New fuel filter. Also checked all vacuum lines. Idles good unless you try to move. Heres where I need some help. Fuel pressure is anywhere from 25 to 30 with engine off key on, but I have to turn the key on and off a couple of times to get it to build up to that. Drops back to 20 after several hours. When running never gets over 20. When car wants to stall and chugs, it drops to about 15. This I think is way to low. Is it? Next if it is the fuel pump. Do you have to drop the tank to change it? Looked under the rear seat and didn't find an access hole. Or can I put an electric pump in line?

[Mikey_K]

Much cheaper (and easier to replace) than the fuel pump, the fuel pressure regulator is a diaphragm and spring right on top of the TBI.

You can order a replacement diaphragm from NAPA, or wherever you get parts. I didn't need to replace mine (problem was a vacuum leak at the MAP sensor), but there *was* quite a bit of debris and sludge under the cap. I'd guess too much crud under there could give you the variable readings you're seeing.

When you pull off the whole air cleaner assembly, it's the sort of rounded- rectangular thing (an inch or so long by a little bit bigger than that wide?), held tight by four? screws. Just make sure you replace everything in the same orientation. Sketch yourself a picture of how it came apart, if you want to be careful. The Haynes manual has a good photo of the location.

[thenn3025]

That's something I did not even know about. I'll check it out. It is pretty crappy in that area.

[GM Line Rat]

Originally Posted by thenn3025

Next if it is the fuel pump. Do you have to drop the tank to change it? Looked under the rear seat and didn't find an access hole. Or can I put an electric pump in line?

Have you replaced the fuel filter on the car recently? If not, start with a new fuel filter and see if it increases the fuel pressure readings? If not, No harm done.......But the either the Fuel pump is weak, or the Fuel pump sock itself is clogged /Dirty and needs to be replaced (Both of which require Dropping the fuel Tank). Dropping the fuel tank in the Geo is child play compared to other Cars.
1. Disconnect the Battery ground wire.
2. Remove the lower rear seat and disconnect the fuel pump wire harness, then push the rubber grommet /harness thru the floor pan.
3. Jack up the rear end of the car approx 18" off the ground and support on both sides of the car with jackstands and wheel chocks in the front of the car.
4. Drain as much fuel as you can from the tank by removing the fuel filler hose from the fuel tank, then running a siphon hose to a spare 5 Gal empty fuel can. Have a spare can ready in case there is more than 5 Gal of fuel in the tank. If the filler hose wont come off easy, you can do this process after the fuel tank is slightly lowered down.
5. Now get a Auto floor jack and a small (18" X18") Piece of Plywood, put the plywood on the base of the floorjack, then center the floorjack under the middle of the fuel tank.
6. Pump the jack up just enough to support the fuel tank......Then remove the 4 Bolts that hold the fuel tank in place to the car.
7. Lower the fuel tank down JUST ENOUGH To remove any other hoses connected to the fuel tank from the Fuel Filter, Pull the fuel pump harness clear of anything it could catch on and put it on top the tank.
8. Then lower the floor jack all the way down and pull the fuel tank out from under the car.
9. Now take a garden hose/Small scrub brush/ Soap and "Gently" wash all the dirt / debris off the TOP of the fuel tank that's been on there for years!.....Let the top of the tank Air Dry.
10. To Access the fuel pump Assy is by removing the screws around fuel sender base cover base , and lifting the cover up. Be gentle when doing this and guide the assy out of the tank!
11. Drain ALL the remaining fuel in the bottom of the tank (Dont save it, get rid of it.....It probably has some rust in it).
12. Now Check/ clean out the bottom of the fuel tank is as you can to get rid of any sediment / Rust in the bottom of the tank.
13. Buy a NEW "AC-DELCO" / GM fuel pump kit that includes rubber seals, wire connections and a new Fuel filter sock in it.
14. Make note or take pics with a digital camera of the fuel pump assembly BEFORE you take it apart as a reference in case you forget the Re-Install procedure........Reverse this procedure to re-install the whole setup.

Here a couple of good pics you can use to see the process. If you haven't installed a new fuel filter, and you change the fuel pump.........Install a NEW fuel filter also whilke the tanks out of the car (It's easier).

Fuel Filter 1



Fuel Filter 2



Top of Fuel Tank

[thenn3025]

OK. Decided to take the tank off and have a look at the pump. Insaide of tank wasn't to bad. All though when I drained what was left in it that gas had a pale yellow color. Probably some rust. Did see a tiny bit of water also. After I had pump out I put it in a small pail of gas and turned it on. Is fuel suppose to squirt out the bottom of the motor? As it was running fuel was coming out all the way around the bottom. Not just a little. I did have my pressure gauge hooked up, so it was deadheaded. Took the gauge right up to 34 psi. I have another junker out back. I will probably take that tank off and put it on this one and see what happens.
I also looked at that diagrapham in the throttle body. Looked ok, but swapped it with one out of the other one. After that either one only made matters worse. Pressure would go to 20 and when I started it would drop to 15 and then go down till car stalled.