I just installed a Holley 255lph pump and now the car doesn't want to run right. Anytime you let off the gas in any gear the car wants to stall. I have to fuel pressure backed off just about as much as I can, and I checked the TPS voltage earlier and at idle it is sitting at like 3.4 volts...I couldn't get it any lower than 2.1...Also when you are driving it, and let the rpms go below 800 or so, the car starts bucking and barely wants to run...what's the deal?

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1989 Chevrolet IROC-Z28 TPI ZZ4 with TH700R4 and 2.77:1 rearend gears:
-Gutted Air Boxes, Throttlebody coolant bypass, Hypertech Air Foil, Accell Superram Base Intake, Crane AFPR, AC delete, Smop pump delete, Hooker 1 5/8 Headers, Holley Ignition Module, Hypertech Custom PROM, B&M Megashifter...I know there is more, I just can't think of it right now!

 

89,

You should be checking the TPS voltage at the 'A' and 'B' terminals (normally the top two terminals). You must get below 0.61VDC across these terminals to run correctly. Anything above that voltage is going to start fooling the ECM into an acceleration mode and give you a really rich mixture.



If you can't get the correct voltage, you may have a failing TPS, or may have lost the reference ground at the 'A' terminal on the TPS. To check the ground, shut off the ignition and measure the resistance between the 'A' terminal and a good engine ground. There should be less than 1 ohm.

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Later,
Vader
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"Make Me Bad"
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