Things that cause a fuel pressure drop befire TBI

[Terminal_Crazy]

Hiya

Just a thought, does your FPR use a vacuum reference off the manifold like the LT1?

Mitch

[brian617]

It could be volume...however that still doesnt explain the pressure drop. Something is causing it to happen only in a certain rpm range...and then it fixes itself at WOT.

Sure it does, if the volume demand can't be met then a drop in pressure results. Pull the line from the back of the throttle body and run the pump manually into a measuring container and calculate your Gallons Per Minute.

[Bonzen]

Hiya

Just a thought, does your FPR use a vacuum reference off the manifold like the LT1?

Mitch

No it's left open to the air per the aeromotive instructions for a non-forced induction TBI motor

[Bonzen]

Sure it does, if the volume demand can't be met then a drop in pressure results. Pull the line from the back of the throttle body and run the pump manually into a measuring container and calculate your Gallons Per Minute.

Explain...I'm picturing the fuel injectors opening at a faster duration and for a longer period of time...and that would evacuate the fuel in the line causing a pressure drop?

[brian617]

Imagine a restriction between the pump and the TBI, example a smaller orifice in a fitting. At rest and low fuel volume desired the pump can maintain pressure and volume. Now at a larger throttle opening more fuel volume desired the fuel between the restriction and the TBI is quickly used and the pump is unable to re supply the fuel volume quickly enough because of the restriction. Between the pump and the restriction the pressure would probably remain fairly constant.

[Hog]

"and then it fixes itself at WOT."

The problem fixes itself at WOT though.

peace
Hog

[Bonzen]

Hiya

Just a thought, does your FPR use a vacuum reference off the manifold like the LT1?

Mitch

No it does not. Its open to the air per the Aeromotive instructions for installation on a TBI equipped motor.

[Bonzen]

Imagine a restriction between the pump and the TBI, example a smaller orifice in a fitting. At rest and low fuel volume desired the pump can maintain pressure and volume. Now at a larger throttle opening more fuel volume desired the fuel between the restriction and the TBI is quickly used and the pump is unable to re supply the fuel volume quickly enough because of the restriction. Between the pump and the restriction the pressure would probably remain fairly constant.

Why did this not occur with the old engine (same pump/fuel lines/etc)

Granted the new engine has a little more compression and a slightly hotter cam but that's it. Same fuel injectors/same heads.

[Bonzen]

Attachment 10906should I just throw this thing at it? lol.

[brian617]

Have you checked you gallons per hour?

[lionelhutz]

I'd take the return line off the tank, put it into a gas can and then power the pump and time how long it takes to pump 1/2 or 1 gallon of gas. Then, you'll know how well the fuel system is performing at pressure.

[Bonzen]

Have you checked you gallons per hour?

No not yet. Is there a standard or baseline of GPH that a slightly modified BBC needs to run correctly?