High RPM Fuel Pressure Drop

[BBBT]

Hello. I've got some problems with fuel delivery on my next configuration:

• 360 N/A stroker Magnum, about 500 HP.
• Holley EFI Terminator.
• 12-890 Holley fuel pump.
• Holley 100 micron fuel pre-filter & 10 micron post filter.
• 12-846 fuel pressure regulator installed after fuel rails.
• -8AN line from tank to pump, -6AN feed line to Terminator & -6AN return line from regulator.

So at this point, FPR set to 43 psi at idle (with disconnected vacuum line). It works fine and keeps this pressure for about 2000-2500 RPM (with connected vacuum line pressure is about 38 psi). After that, at higher RPM pressure seriously drops to 15-20 psi sometimes to 6 psi. When pedal pushed abruptly on neutral, I can see the same thing.

I've already changed the fuel pump to another brand new 12-890 from box, installed fuel pump relay, pump feed & ground now directly from battery, installed another new FPR, check & clean all the filters & fuel lines, nothing happened. I also tried to feed pump with gas directly from canister. Voltage on alternator is about 14V. At this point, I've dismounted Terminator throttle body, check fuel rail lines, but they are good. Really don't know what to do now, already have a headache from all of it. Can you advice something to me, what I have missing?

P.S. Few months and about 500 miles ago, there was same configuration on this car with only 12-600 fuel pump, and pump feeding from Terminator. All other parts were same and it has worked good, without any fuel problems.

[Danny Cabral]

Is this fuel pump cavitation? Where is the fuel pump & pre-filter located in relation to the fuel tank? How long is the suction hose? Is there a restriction somewhere in the fuel system plumbing?

[BBBT]

Is this fuel pump cavitation? Where is the fuel pump & pre-filter located in relation to the fuel tank? How long is the suction hose? Is there a restriction somewhere in the fuel system plumbing?

It doesn't look like cavitation, but after ~10-15 minutes of work, the pump is really hot. Pump located at the middle of frame, it's about 4-5 feet from tank. As I say, to exclude problems from pump feeding, I connected a short hose to inlet port of pump and put other end in canister, no effect. There is no visual restrictions or clogging in fuel lines. I want to try add check valve after pump, and change feed line to -AN from pump to Terminator.

[Danny Cabral]

Pump located at the middle of frame, it's about 4-5 feet from tank.

This is not a good fuel pump location, especially long term use.

As I say, to exclude problems from pump feeding, I connected a short hose to inlet port of pump and put other end in canister, no effect. There is no visual restrictions or clogging in fuel lines.

Then I'm not sure what the problem is.

I want to try add check valve after pump...

No need for that.

[BBBT]

I've done what I spoke of above; changed feed line from pump to EFI. Problem has gone at this moment. Ride about 30-40 minutes with pedal in the floor and pressure stay at 39-40 psi at full throttle. Just change 4 feet -6AN hose to -8AN hose with check valve, and the pressure drops are gone. Don't know how it works, but it does.

[Danny Cabral]

Just changed 4 feet -6AN hose to -8AN hose with check valve, and the pressure drops are gone. Don't know how it works, but it does.

You had a restriction somewhere in that -6AN hose/fittings. -6AN hose/fittings won't cause a fuel pressure drop. My entire fuel system is plumbed with -6AN hose & fittings.

[BBBT]

It was likely some problem with the 10 micron filter in this line, that was deleted from there too, because hose & fittings are good. It's strange, because I took it apart & cleaned it with compressed air, so it has good flow before installation checked by my mouth. I'll try to install another new one tomorrow and see what would change.

[Danny Cabral]

Well I'm glad you found the problem. Thanks for the update.