Fuel Pressure Wont Rise!!


Ok, ive been trying to figure out my knock problem for a while now, and now I know the problem. I hooked up an oil-filled guage to the fuel rail, and just went for a spin. Idle fuel pressure PSI (line off) is set at 44 psi. When I hit any amount of boost, whether it be 5 psi or 15 psi, the pressure on the guage does not rise at all!

I have a new walbro 340 pump, new adj. fuel pressure regulator (an accufab one), and a fairly new gas filter. When I dropped the tank to replace the fuel pump (my car was sitting for 6 years), unbelieveably there was not one piece of rust in the tank, which leades me to believe that there is no rust in my fuel lines. I also have used MSD 50s on the car.

What can the problem be? I dont get any knock (surprisingly) until about 15 psi (about 4-7 degrees).

Can it be the injectors? Clogged fuel filter? Clogged fuel rail (with rust possibly)???:mad: :mad: :mad:
My car had similar issues. One (of the many) problems was that my accufab regulator had a piece of junk wedged under the puck inside of it. I almost bought a different one but decided to take it apart first. I was careful and didn't screw up the gasket. I found that thing, took it out, put it back together and it's been working ever since. Before you do that though, take the hose off the regulator and try and blow through it. If this is difficult then your hardline is probably plugged. This is another problem I had. It's worth a shot, especially if you have pressure on the rail when you shut off the key. Speaking of that, if you have pressure on the rail when you shut off the car then the regulator is probably fine. Sorry this is jumbled. Hope it helps. james
Guys, im an idiot..I forgot to hook up the vacuum line on top of the regulator..It works perfect now, im getting the correct fuel psi per pound of boost.

It turned out my stationary fuel pressure gauge was off by 5 psi (i was tuning the damn car with a static fuel pressure of only 38 psi)..

Im still getting around 6-9 degrees knock at WOT when I stay on it and I hit about 16 psi...But the knock would eventually go down while I stay on it..:confused: Maybe clogged or sticky injectors??

I was actually running my car at about 55 psi static fuel pressure (line off) for a couple months (before I realized my MAF was bad)...Could that have screwed up my injectors???
You have a modern chip? As in TurboTweak or equivalent? if there is such a thing ;)

Any ways, it could be false knock also, as in from shifts, or something metal hitting something.
Forgot to mention, its a low-mileage, stock unopened motor with GM replacement valve springs, TurboTweak 93 chip, MSD50s, THDP, 2 1/2 in. Magnaflows, stock turbo, stock intercooler, and a power-plate. All new vacuum lines are in too, new hot-wired walbro, and new adj. fuel press. regulator.

I can think of a few things:

(1) Maybe the plugs are fouled from running sooo rich for so long?
(2) Exhaust leak on the driver's side header (I can hear a slight ticking noise like an exhaust leak noise).
(3) Sticky injectors
(4) Maybe I need to adjust the base fuel/timing setting on the TT chip??
(5) Replace the fuel filter again?
(6) Maybe the powerplate is causing this knock?
Alright, does the knock climb up as in .3-.5-1.2-1.7-3.5? OR 3.2-2.5-6.6-.2-25.4??

If it climbs, its real, if its bounces around and isnt the same every time you get on it. I'd say FALSE knock.

Make sure nothing is hitting anything, as in if you have a metal inlet pipe from the MAF to the compressor housing, it isnt hitting the alternator area. (I've seen one of the metal pipes someone sells do that.)

The knock appears to stay steady and eventually increase it seems (I let off the pedal)..:eek:

I noticed a condensation mark (when I put top-engine cleaner yesterday) around the (previously) welded driver side header (between cylind. 3&5) that most likely leaks again.

This knock really only occurs in 4th gear (at around 90-100 mph, about 2-6 degrees).

SO, the three things that I can think of now that are causing this knock are:
(1) The header leak
(2) Sticky/bad injector
(3) False knock (maybe from the downpipe, but I doubt it, it looks cleared of everything).

Everything else on the motor is new (coil pack, plugs, wires, fuel filter, walbro 340, good MAF sensor, no loose hoses, new vacuum hoses, new fuel pressure reg., etc.)

My next step is to put some race gas to see if its real or false knock, but im willing to bet now that its the header leak causing this problem...
So it gets heavy at 90-100 mph? Are you in OD? If so, do it in Drive and see if it has any difference, because i believe around 85 mph, the trans will shift into OD, even if you're WOT.

Try it in Drive, (unless you already are) and then get back to us. :wink: