Fuel Pressure at The Rails will Vette FFR

[AU Doc]

I just added a Holley fuel pressure sensor to my Holley Dominator EFI to help diagnose some issues with my engine. It turned out my (new) fuel filter regulator (FFR) had failed, and I was showing 109 psi at the rails.

I replaced the FFR, and first startup it was showing 68 psi or so at idle. I didn't have time to drive it, so I pretty much started it and shut it back off. I finally had a chance to start it up gain last night, and it's showing 71/72 psi at the rails. Is this normal, or is there something else going on with my setup? I would think if I'd plumbed it incorrectly (i.e., swapped the inlet and return on the FFR), I would not get any fuel to the rails, but maybe that's not correct.

Any help is much appreciated! After all the effort in doing this LS swap, I'd much rather be driving my car than sorting out all the gremlins I've run across

[rickpaw]

Just a guess, but have you scaled the sensor correctly? Did you verify the pressure at the fuel rail using a mechanical gauge? I used a Wix FFR and it showed a steady 58 at the rails, using a mechanical gauge.

Now I'm running Rick's restomod tank with the 5th gen Camaro module/Speedhut electronic fuel pressure gauge - and it shows 58 psi as well.

[AU Doc]

I wondered about the gauge scaling as well, but it's "supposed" to be the Holley branded sensor. So I assumed the scaling should be correct. I don't have a mechanical gauge to double check with.

[rickpaw]

If the fuel rail is an OEM unit, it should have a Schrader valve at the end. AutoZone rents out a fuel pressure gauge that screws onto the valve. You can try that.

[AU Doc]

Good tip! I'll check with AutoZone.

[AU Doc]

I've asked over on the Holley forum whether or not the sensor "should" require calibration, and they response there is it should NOT. So this would imply the reading is correct.

While I'm waiting on an opportunity to rent another gauge, any suggestions on what could be the cause of the high fuel pressure? Am I correct that connecting the FFR backwards should not allow fuel to make it to the rails?

[rickpaw]

Well, could be bad luck, but you may have a bad FFR, again.

I've read somewhere that if you connect the FFR backwards, it would cause a low pressure situation, not the high pressure as you're experiencing. You didn't list the brand, but others, myself included, have used the Napa/Wix branded FFR. They seem to have the least issue.

[AU Doc]

I don't actually know what brand the filter is. It's the Tanks Inc. filter, which I'm sure is another brand with their PN on it.

I'll pick up a WIX FFR before I do anything too drastic like dropping the tank (it's full - FULL - of gas or I probably would have done it already).

[andrewb70]

Paul,

Make sure you plumb it correctly, if you run it even once backwards, it will kill the FPR. The inlet is the fitting that is offset, and the return back to the tank is the center fitting.

Andrew

[AU Doc]

The fuel pump side is the only question, and that’s only because I can’t see it. I’m pretty sure it’s right. I’ve got the return on the passenger side fitting and the supply on the drivers side, which should be correct.

It’s just my OCD acting up :-)

[CarlC]

What fuel pump is being used?

[AU Doc]

Walbro 255 lph.

[CarlC]

That pump should be fine with the C5 FFR. As Andrew mentioned, confirm the inlet/outlet and check the pressure at the rail with a mechanical gauge.

If the fuel pressure is still high then something is wrong either with the FFR or the return line is plugged.

[cpd004]

A buddy had a similar high reading which turned out to be a tank venting issue. One thing you can try is removing the gas cap to see if it comes down. If so, the tank isn't vented properly.

[AU Doc]

A buddy had a similar high reading which turned out to be a tank venting issue. One thing you can try is removing the gas cap to see if it comes down. If so, the tank isn't vented properly.

That's a good idea! I'm going to hope that's the fix I'll let you know what turns up.

[AU Doc]

No luck on either front. I borrowed a Snap-On gauge, and it's reading just a little above what my sensor shows - both at the rail. Still 70-75 psi, and that's with the gas cap removed.

I guess I'll plan to drop the tank and double check my lines. I may go ahead and replace the pump while I've got it down. I also plan on replacing the FFR with the WIX unit I got today.

BTW, NAPA is crazy expensive! About $30 more expensive than ordering it form Amazon.

[AU Doc]

Slight audible. Since I have to empty my tank, anyway. I'm going to run a line from my return on my FFR to my can. I'll check the fuel pressure with the pump pumping gas into my can. That should at least tell me if the return is blocked. If my pressures are still 70-75 psi, I may just replace the FFR before I drop the tank and replace the pump.

[dhutton]

I don’t see how a defective pump would create pressure that is too high. I see little point in replacing it...

Don

[AU Doc]

I think I’ll risk it and just swap the regulator - again. With the return dumping into a gas can I’m getting the same pressure. Fingers crossed!!

[AU Doc]

I guess that last one was a little ambiguous :-)



With the old regulator I ran the return to a gas can to empty the tank. With the engine running it was still showing 71 or so psi. So that certainly looks like the regulator.

Swapped out the regulator and the new one is showing 56-58 psi. Now the question is going to be whether or not there’s something else going on that’s killing the regulator. Hopefully I can get everything back together and put a few miles on the car this afternoon.