Fuel Pressure Drop - Baffled...

[Simace]

Problem:
From -18 to 0 psi, fuel pressure rises to about 46psi. At 1psi the fuel pressure drops down to where it normally is at idle (about 38psi). As boost comes on, fuel pressure rises at what appears to be .5psi for every 1psi of boost (not 1:1 ratio).

What I've done so far:
-Replaced vaccum hoses
-Replaced FPR
-Bypassed FPR Solenoid
-Replaced Hotwired Supra FP with Walbro FP (later reinstalled Supra)
-Re-did the Hotwire
-Swapped TruBoost controller for Halman PRO (MBC)
-Pressure tested (slight leak at throttle body butterfly - spring area)

I don't know what else to do or check, so I'm hoping for ideas on what might be causing this.

[ICPREY]

Fuel filter? Didn't see it on your list

[Simace]

I have been told about the fuel filter, and though I do plan on changing it out this weekend, I just don't see how that could possibly be the culprit considering the way fuel pressure rises but then drops (the drop being tied to going from a negative pressure to a positive pressure.)

But I appreciate your input and hope that it does cure this weird symptom.

FWIW: This weekend I'll also be doing spark plugs, motor oil, installing a new UEGO WB sensor and, if time permits, differential.

[Frostedbutts]

Wouldn't a clogged filter cause your fuel pressure to increase? Like putting your thumb over the opening of a hose.

[RealMcCoy]

What kind of fuel pressure regulator?

Wouldn't a clogged filter cause your fuel pressure to increase? Like putting your thumb over the opening of a hose.

Not when you're measuring after the restriction...

[rawavr4]

Faulty gauge? Whats the wideband read from -18-0?

[Ninja Performance]

Faulty gauge? Whats the wideband read from -18-0?

This was my thought. What are you measuring the fuel pressure with?

-Chris

[Simace]

Fuel filter replaced. Problem persists. Any other suggestions I can try now since I'm still under the hood at the moment wiring in a serial cable to the uego wb02 so I can log using evoscan?

[Simace]

Both the adjustable FPR has a fuel pressure gauge (in engine bay) and I have a Prosport Fuel Pressure gauge (electric and in cabin). Both read the same at idle and if I use the FPR to up the fuel pressure or bring it down, both gauges show the change.

I don't know how i can monitor both gauges while actually driving the car. But I figured since both are showing same change when the fpr is used to set fuel pressure, I was good.

As to the AFR during this episode, I'm still putting in the wiring as i mentioned earlier. So I don't know the AFR. NB02's show .95/.96 WOT at 1bar, fwiw.

[AdamVR4]

As your fuel pressure drops and then fails to keep up with boost, do your IDC's rise higher than usual, the ignition timing stays low and the car is SLOW? I guess what I'm wondering... Did the fuel pressure ever rise 1:1 with boost? If so, when? What changed?