Fuel pressure drop

[DRJDVM's '69]

Changed from carb to Holley EFI in Dec 2021- had some stumbling issue and some pinging when I tried to jump on it…….roll in and it was fine. On the data log it looked like I was getting a drop in FP based on the way the car was acting- installed a FP sensor so the EFI could monitor the actual number and confirmed that I was getting an intermittent drop on FP. Dropped the tank, pulled the pump, and sent it to Aeromotive- they stated it was slightly out of specs, so I paid to have them rebuild it. Inspected the in-tank fuel filter and it was clean. Re-installed everything, new fuel lines, made sure all my wires and grounds were good. Did all of this toward the end of 2022 and the car ran fine but I didn’t beat on it, with the plan to get it remote tuned in 2023. If I take it easy, the car seems to run fine.
Did a remote tune with Andrew Borodin and I’m still getting some pinging when I am at lower RPM and jump on it and randomly it will stumble and sputter and the AFR will go crazy. Happened mostly after I got on it and then go back to cruising. Data logs show I am still getting weird drops in FP. Other times its rock steady around 63 PSI.
So, I’ve got some fuel delivery issues, but I’m not sure where/why. Pump is supposed to be rebuilt and good to go…. New regulator… new fuel lines (would prefer an 8 AN supply but I was trying to limit the number of adapters to make that happen). So before I just start to throw parts at this, I was looking for some input on narrowing down the cause. I’m hoping to retain my current tank rather than drop $2500 on a new tank and pump set up etc. I’m fine with a different fuel pump, regulator etc, but I don’t want to start all over with a new tank design etc.

434 ci SBC, naturally aspirated.
10:7 compression ratio
Around 600 HP
Holley Sniper HOL- 550-1003 Terminator X EFI system
Ricks Hot Rod SS tank purchased around 2005 (no provision for the new drop in pumps etc)- standard vent in tank, no vented cap
Aeromotive A1000 in tank pump- rebuilt around June 2022
Holley 12-889 Regulator/filter- non-adjustable- new in Dec 2021
Fuel supply to TB 6 AN earls braided line (originally had an 8 AN supply but couldn’t find single adapter to have FP sender and step down to 6 AN to attach to TB)
Return is 8 AN with Holley regulator/filter mounted back by tank)
Completely rewired the car with AAW kit in 2004 and its has worked flawlessly. FP is run right off the AAW kit

[camcojb]

What are you using to vent the tank?

[OLDFLM]

0The restomod tanks are inexpensive and allow the drop-in GM fuel module.

I'm running the Holley Terminator TBI EFI on my 440cid at the same power level with no issues... also tuned by Andrew!

[dontlifttoshift]

Where is that regulator mounted?

It's this one right? https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/efi_regulators/parts/12-889

Which Sniper do you have? Does it not have a regulator built in? I have a feeling that a regulator plumbed between the throttle body and the tank in the return line would solve this.

[DRJDVM's '69]

The tank is just vented through the vent line on the top of the Rick’s tank. Again, this tank was purchased back in 2005-06, so it’s not the same design as now. Looks like it’s just a tube into the tank and I have a hose running up the rail and looped to have the end sit up higher. Non vented cap

I had thought about the venting…. The FP issue seems to happen at any fuel lever… hot or cold… short drive or long….. so not thinking tank pressure or fuel temp

The HOLLEY EFI TB is the system that looks like a Holley double pumper….. no built in regulator. I have the regulator plumbed info the supply line mounted back near the tank, so the return like is probably about 2-3 ft max

My car is the full pro-touring theme so don’t want to ditch the Ricks SS tank …. Just hoping I can find a different pump and regulator set up that works with the current tank set up

[Vegas69]

System voltage when the issue arises? If it's doing it with a full tank, then I doubt it's a tank baffle issue.

[DRJDVM's '69]

Need to look at the data log more...we ran out of time... but no system voltage drop at times of FP drop but obviously it could be a drop at the actual pump

[Vegas69]

I just noticed you stated your regulator is back near the tank. It's fuzzy, but I believe it's often recommended that the regulator be in the engine compartment to avoid a loss of fuel pressure under high demand. That way you have full volume near the fuel rail vs. 15' away. With a carb and bowl, you could probably get away with it.

[DRJDVM's '69]

The Holley regulator/filter is kind of designed and marketed as using close to the tank… short return line etc Less heat soak of lines

I know plenty of guys…. Including Jody….. run their regulators back by the tank…. Similar to OEM systems that don’t have any regulators anywhere near the engine bay

I’m kind of leaning towards the regulator being the issue… it’s new but you know how that goes…

[DRJDVM's '69]

https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/efi_regulators/parts/12-889

The “overview” info, as well as the picture, say it can be mounted near the tank

[dontlifttoshift]

Install this. https://www.holley.com/products/fuel_systems/fuel_pumps_regulators_and_filters/regulators/efi_regulators/parts/12-846

Like it shows in figure 2B on page 2 with the regulator near but after the throttle body. https://documents.holley.com/199r10575rev3.pdf


The regulator you have is the same in operation as a Corvette filter/regulator and works fine in stockish applications. When you go from needing not much fuel to a large amount of fuel it just doesn't react fast enough and it is too far away.

[DRJDVM's '69]

Well its currently set up like 2a... the regulator is just back near the tank/pump.

I don't see a way to do 2b.... that's going to require a fuel log and the return coming off near the front of the carb/TB and then looping and going back.....going to be really hard to do that, both mounting any regulator and plumbing

[Vegas69]

The Holley regulator/filter is kind of designed and marketed as using close to the tank… short return line etc Less heat soak of lines

I know plenty of guys…. Including Jody….. run their regulators back by the tank…. Similar to OEM systems that don’t have any regulators anywhere near the engine bay

I’m kind of leaning towards the regulator being the issue… it’s new but you know how that goes…

Definitely worth a shot before a major replumb or reconfiguration.