Got myself confused on setting FP

[jsawduste]

Stroker has been giving me idling problems lately. 75% of the time it would idle fine. The other 25% it would be high or low.

Found a crack in the hard plastic line going to the FP regulator. Repaired it.

Vac hose ON was at 37 lbs. of FP. Bumped it up to 42 lbs with repaired line and the vac hose ON.

Here is where I am getting confused.

Vac drops under load and the engine wants more fuel.

If I am setting the regulator to 42 lbs with the hose ON. When the engine goes under load (vac drops) then my FP will be a nominal number (8-10 lbs) LOWER under load.

So my 42 lbs drops to a 32-34 under load.

Or

Should I be setting the FP with the hose OFF to around 50-52 lbs so when the hose is reconnected I see a 42 ish lb running FP ?

BUT

The A/F ratio gauge doesn't seem to support an overly lean mix under load and in cruise mode shows an nice 14.7 ish A/F ratio with 42 lbs and hose on.

me> > Confused...............

[jsawduste]

Update, put almost a 100 miles of combined city/hwy with the 42 lbs FP hose ON.

Idle is much improved as is general "feel" of the engine. A/F ratio`s still in ball park. Am going to bump FP up a few more lbs withe the hose ON and see how it runs. With time given to the ECM to learn the new settings.

Suspecting the ECM has been running the injectors at an advanced duty cycle to compensate for the lower fuel pressure. With FP coming up the ECM is beginning to have a more precise control of injector duty cycle.

Guesstimate mileage increase as well.

Welcome comments and experiences of others.

[Cheromaniac]

If I am setting the regulator to 42 lbs with the hose ON. When the engine goes under load (vac drops) then my FP will be a nominal number (8-10 lbs) LOWER under load.

So my 42 lbs drops to a 32-34 under load.

You've got that backwards John. Your next statement is correct:

Should I be setting the FP with the hose OFF to around 50-52 lbs so when the hose is reconnected I see a 42 ish lb running FP ?

When you have the engine under load with a low intake manifold vacuum, the fuel pressure should rise so that the injectors will supply more fuel. At idle with the vacuum attached to the FP regulator, the fuel pressure should be near 40psi.

[jsawduste]

Understood and thanks. Confusing for me

The engine is running very well at 42 lbs. I still want to add a few more pounds and see what happens.

[Cheromaniac]

The A/F ratio gauge doesn't seem to support an overly lean mix under load

I assume you have a wideband AFR gauge so what are your AFR's under WOT? If they're much higher than 13.0:1 you can raise the fuel pressure even further. Try it in 2psi increments until you find the "sweet spot". It'll be difficult to get a "flatline" 13.0:1 AFR across the whole rpm range due to the stock PCM programming (usually leaner at low rpm and goes richer at higher rpm to prevent the cats from burning up) but you can get it close.
Your closed loop AFR is where it should be so the factory O2 sensor is functioning correctly.