TBI fuel pressure and regulator

95Yukon · December 18, 2001

What is the best way to accurately determine how much fuel pressure is going to the injectors themselves? I know how to check the fuel pump psi by putting the gauge on a T fitting on the inlet side of the TBI and turning the key on.. (per my book it should read 60-66 psi fuel pump pressure)

Now, the regulator should have 9-13 psi going into the injectors, and bypass the rest back to the tank..

How do I accurately determine my regulator pressure?

I want to check this because I noticed that when my gas tank drops below 1/4 tank, my performance seems to be a bit less than normal. If the fuel tank level is above 1/2, it picks right back up. The only thing I can think of is the return line is more deeply submerged, creating more resistance in the return line, causing a slight rise in fuel pressure going to the injectors. I know there are kits to tweak the pressure to fine tune the performance but I want to find out what the pressure is at the injectors now to determine if this could be it. I want to check it with the tank full and below 1/4 to see if it varies. Since it runs better with more gas in the tank, I figure I may want to increase my regulator pressure a bit to offset the performance loss at low fuel levels. Also I just changed my plugs and the "old" ones (11 months, 9K miles old) looked a little more lean than I am used to seeing.

Anyone? - thx

dougmac · December 22, 2001

The pressure at the inlet of the TBI unit is the injector pressure. The pressure should be 9-13 pounds if I remember correctly.

Were did the 60-66 psi figure come from? Could this specification be for a port injected truck? ???

Fuel pressure beyond the maximum can cause fuel to leak past the injector. Messing with the fuel pressure is a bad idea. The better approach would be to identify and fix the problem that is causing low performance.

Doug

95Yukon · December 22, 2001

I don't want to push the pressure past maximum, just want to be sure it is at at least the minimum to try and find if there is a pressure problem. They sell adjustable fuel pressure regulators to adjust it up or down a few psi and since the stock regulator is set at the factory and non adjustable, I thought that if the regulator was starting to have a problem I would replace it with one of the adjustable units.

My book had a misprint. through 95, it is 9-13 psi. 96 and up is 60psi for SFI systems. Mines a 95. It should have said 96 and up, not 95 and up so it messed me up. It runs perfect, but its just strange the way it seems to have that little bit extra when the tank has more fuel in it.

The difference is very slight, and I know this truck real well so I notice everything. We just had some cooler dry weather come in here, and it feels like it picked up 20hp which far exceeds the little varience I get at different fuel levels. It loves this cool air. I'll probably leave the regulator alone for now, maybe just do a pressure check on the inlet side for 9-12 lbs. to be sure its in the correct range.