Fuel Pressure Issues (1 Viewer)

[projectfj]

Background: 79' FJ40, sbc350, Edelbrock Performer 600cfm carb, Mr Gasket 4-7 psi electric fuel pump, Holley 4-9 psi adjustable fuel pressure regulator, Holley mechanical fuel pressure gauge.

Problem: At start up my fuel filter bulb is full and I'm getting 5 psi no matter how I adjust the fuel pressure regulator. As it warms up, less gas is visible in the fuel filter bulb and the fuel pressure drops to 3.5 psi no matter how I adjust it. Eventually, no fuel is visible in the fuel filter bulb and my fj dies (starved of gas I suppose).

Does this sound like a bad fuel pump? or something else?

 

[spotcruiser]

Could be, or maybe you're drawing a vacuum on the tank. Sounds like the pump is not putting out more than 5 psi at any point. Those pumps are pretty inexpensive. I'd get another one, just for a trail spare, and drop it in there to see if the results are different.

Background: 79' FJ40, sbc350, Edelbrock Performer 600cfm carb, Mr Gasket 4-7 psi electric fuel pump, Holley 4-9 psi adjustable fuel pressure regulator, Holley mechanical fuel pressure gauge.

Problem: At start up my fuel filter bulb is full and I'm getting 5 psi no matter how I adjust the fuel pressure regulator. As it warms up, less gas is visible in the fuel filter bulb and the fuel pressure drops to 3.5 psi no matter how I adjust it. Eventually, no fuel is visible in the fuel filter bulb and my fj dies (starved of gas I suppose).

Does this sound like a bad fuel pump? or something else?

 

[SouthMS40]

So your pump is a 4-7 psi with a regulator of 4-9 psi. Some pumps are rated at the outlet with no lines attached. Once you plumb it your going to only see maybe 5 psi due to losses and restrictions. Plus, your pump is too closely matched to your regulator so the regulator isn't doing anything here.

If it were me I'd go buy a bigger pump maybe one that peaks out around 30 psi. This way you know you have sufficient pressure and you're forcing the regulator to do its job. Also be sure your fuel tank is properly vented otherwise you'll draw a vacuum and kill the flow.

Verify the required pressure on that 600 cfm carb. Doesn't seem like you're getting enough fuel to it fast enough it it's sucking the bowl dry and the line. Make your return to tank line do some work too.

Good luck.

 

[projectfj]

Any suggestions on a good fuel pump? I'm sure the lines to the tank have something to do with it since the PO removed all the emissions stuff and didn't properly connect anything. I'm still working out where everything goes since the charcoal canister was removed.

 

[shawnfj40]

A really quick check would be to just take off your gas cap and run it until it either stops or doesn't. If that fixes your problem then you are almost finished.

 

[Downey]

Fuel pressure regulators like to let a pre-determined amount of gas through to the carburetor, but they do not like to be a dam holding back a lot of pressure. To solve this problem you can put a "T" fitting upstream (just ahead of) the regulator, with one line going to the regulator, the other line a return to the tank.

 

[projectfj]

I took off the gas cap with the same result as before. Not too long ago I "fixed" the problem with pressure buildup in my tank by venting it. It is doing way better as far as not spewing air at me when I take the gas cap off.

I'll get a new pump with a larger flow rate as suggested as well as put a T fitting before the regulator to the return line. Any opinions on a good electric fuel pump? Am I missing anything?

 

[projectfj]

Update: From the tank I have a Mr Gasket fuel filter (PN 9748), a Holley black electric fuel pump (PN 12-815-1), up to a T that splits to my return line and another fuel filter before my Holley fuel pressure regulator (PN 12-803) with gauge (PN 26-500), which then goes to my Edelbrock Performer 600cfm carb. However, I'm still only getting 2.5-3 psi according to my gauge. When I felt the fuel pump, it was hot around the top. What am I doing wrong?

 

[projectfj]

New update (even if I'm just talking to myself somebody might run into the same problem as me one day): figured out that I wasn't getting fuel pressure, because the 3/8 in fuel line I had going to the return line was too big (figured it out when I squeezed the line and the fuel pressure shot up). So I figure if I swap it with 1/4 in, less fuel to the return and more to the carb. The 3 in of hose I used didn't drop it much, so I got 2 foot, looped it, and now I have enough pressure that the regulator is now adjustable as it should be. Might add a valve to the line eventually or figure out a better way to cut my return line flow.

However, still got a few problems:
1. After getting to operating temp and/or driving around til warm, at idle (red lights, drive thrus, left running,...) The rpms drop to 3-4k and it sounds like it idles funny until after a while it slowly drops rpms and dies out. All the while the fuel pressure on the gauge drops about 0.5psi and it bogs down when I hit the pedal.
2. I noticed when I turn my lights, blinkers, electric fan kicks on, the fuel pump makes less noise and the rpms slightly drop. I also noticed my top 3 fuses are HOT to the touch. Also, though slightly unrelated my tach doesn't work when my wipers are on.

If anybody has suggestions, they are greatly appreciated.

 

[projectfj]

Oh and I swapped the positions of the fuel filters, and that added about 1 psi to the mix.

 

[projectfj]

This morning my carb flooded and started overflowing with gas. This afternoon I did some research and tried the tap method as well as the plug and release before I took the air horn off. I gave it a good cleaning, and adjusted the idle screw. So far the problem seems to be fixed. Also, the RPMs stay around 600 at idle so no more dying at red lights. Now onto the fuse box heat and whatever else the wiring harness has in store for me.