Hey guys, my car seems to run out of steam at around 3500-4000 rpms. So thinking my fuel pressure/supply is off, I bought a gauge and a hypertech fuel pressure regulator.

With key on I get (Engine off): 15 to 20 psi

With engine on at idle: I get 40-41 psi with vaccum hose on.

Now here is my question/problem. If I rev it, my vaccum instantly goes down 8 to 10 psi. I only revved to about 4500 rpm, giving me the feeling that if I had revved higher, I would see it go down further. This test was performed withoug engine load. Should it go up around 4-5 psi as your rev engine higher? Can someone please confirm, I think I need a new fuel pump.

I really think is my problem, and certaintainly feels that way. The car is a beast down low, but loses its momentum at mid to high rpms.

 

If you just turn the key on - not starting engine - by the time the fuel pump shuts off, the pressure should be 43.5psi +/-2.5psi, so anything between 41-46psi is within spec. IT should hold it for a while, before starting to drop slowly.

When you start the engine, with the vacuum line off the FPR, the pressure shoulc be same as above.

When you reconnect the vacuum line, at idle the fuel presure should drop in proportion to engine vacuum. With a stock cam, and at sea level, as much as 8psi drop wouldn't be unusual. With a wilder cam, or at higher elevations, the drop will not be as great.

When you open the throttle, fuel pressure should bump back up toward the "no vacuum" reading.

Sounds like your FPR isn't working correctly. Did you pull the vacuum line off and look for fuel in the vacuum line?

 

The regulator is new. It is an adjustable Hypertech unit. I replace it with this because my fuel pressure was low with the stock unit.

Now the hypertech unit is suppose to be preset for 46 psi with vaccum off, it only regiested 28 psi so I raised the fuel pressure to 46 psi, put the vaccum line on and it went down to 41 psi. This is at idle with vacumm line on, no load, at idle. The needle fluctuates rapidle between 40-42 psi, but I think that is because of the cam's lope.

Now as I rev it with vaccum line on, no load, in Park, the fuel pressure gauge drops 8 to 10 psi as the rpm goes higher. So this has to be my problem, or do I have diagnotics all wrong. I believe that at WOT, Psi should be around 43psi, I am around 32psi.

With key on, engine off you say i should be around the same pressure with engine on at idle with vaccum line on. I am only getting around 20 psi, that is half of what I am getting with engine on. I guess this proves the problem ha?

I am going to replace my fuel filter, as I have never done that since I have owned the car, and probably never has. My lines seem to be ok, there are no leaks, my engines idles smooth now, no codes, but like I said it has no top end whatsoever.

I guess I have a lazy fuel pump if that is even possible, the stock unit is still there.

What do you guys think?