I pulled out my winter beater Fiero from its long summer slumber. Some of you may recognize it from the 25th show.


Getting it ready for this winter's beating, I did a tune up, installed a new starter, etc.
I found that the stock throttle body's fuel pressure regulator seemed to be on the low side (9-ish PSI) and that my BLMs had come up a bit to compensate. In the past, I've always kept my daily driver completely box-stock, but since I've got a few Holley TBIs, I figured rather than take the stock TB apart and dick with shimming the regulator, I'd just put a Holley on.
MISTAKE!
Because the Holley is so much bigger, the tip-in AE is completely wrong and lean bogs every time you open the throttle. I tried fuel pressure settings from 9 all the way to 18 psi. I was able to reduce the lean bog by 18psi, but it was so rich at idle by that point that it was burning my eyes, making my clothes stink, and generally not idling super-great.

WHAT THE HELL? Is everyone else's car with a Holley like this too?

This was a brand-new Holley, btw, never been on a car before.
I have a MPFI Beretta pump in the car, enabling me to run from 9 to 40+ psi if I wanted to.

Hmm, seems somethings wrong there. Have you opened up the manifold port to 2"? Also the intake to head ports should be gasket ported. Are you getting a nice invisable spray pattern? I am running 13 PSI on my 2.5l. Sometimes I think this is too much but the extra fuel returns to the tank.

Maybe your return is clogged. If it were I think a flooding situation would occur. Good luck!

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

quote Originally posted by KurtAKX: I pulled out my winter beater Fiero from its long summer slumber. Some of you may recognize it from the 25th show.

I sure do remember your car, it would have been an honor to park next to you! It was my favorite of the whole show because it's a "Detroit Car", just like mine. It handles Detroit potholes, snow and salt and the best part is that shopping carts always roll away from the car. Sorry I cannot help you on the throttle body issue, here's a bump to the top for you.

Hey Kurt, I believe I ran mine at 15psi or so. It may help to tell you that I could never get my Indy to run right with the port FI fuel pump. Regardless of fuel psi reg setting the high psi pump would not run right with the Holley TBI. After reinstalling the correct TBI pump the car ran fine and fuel trim was close everywhere. I believe the high psi pump is too strong for the TBI regulator.

I've had an inline pressure gauge since I installed the MPFI pump and I monitor fuel pressure all the time. Even with the higher pressure pump, I still have no problems dialing back fuel pressure, even with the stock Rochester FPR.

The car runs just fine on the stock throttle body at anything over 10 psi.
No problems with tip in.
Low 120's BLM at 12psi (128 is ideal)
Everything works fine and when I change the one variable of throttle body diameter, the tip-in 'pump shot' just seems insufficient for the bigger open area of the throttle body.

What I'm feeling seems to make sense logically in that the "accelerator pump" function of the ECM is open loop, and its referencing the TPS to deliver it. Since the Holley has 1.5 times the cross-sectional area, I should probably have roughly 1.5 times the pump shot, but the ECM has no means of compensation.

[This message has been edited by KurtAKX (edited 09-25-2009).]

Question, how are you adjusting the pressure? If at the Holley than your system is being pressurized at 40psi. It seems possible that the Holley regulator is not coping. After all it is not designed to work with a mpfi pump. Then again perhaps the devise is so simple and stocky that it will work. Just a thought.

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White