My buddy has a heavily modified '95 Trans Am that he installed a 58mm Holley throttle body on. He has the LT4 intake manifold ported out to match the 58mm. Whenever he goes wide open throttle DTC 21 pops up in Datamaster. We initially saw the TPS volts go over 5 and Datamaster would not read anything after 100% TPS position. We took the intake elbow off to look at the throttle blades an noticed they are opening way past what they should. It seems the stop is off by about 1/4" from a true WOT. Not what you would expect from a $400 throttle body. If we make up a stop to get a true WOT the TPS volts would only be around 3.8-4.0. Is that okay? Any other ideas would be great and sorry if this doesn't make to some as I am a little scatter brained right now!

Jeff

 

You also have to look at the closed throttle TPS voltage. Has to be below 1V, preferrably around 0.50-0.70V. I have the 58mm Holley, and the TPS had to be slotted to get it down to that value. If you get the closed voltage right, the WOT voltage shouldn't be over 5.0V, assuming you aren't over-rotating excessively. Mine never exhibited that problem. The PCM seems to be able to accept WOT voltages that are lower than 4.0V, but check the closed voltage first.

The "stop" on the Holley is that stamped steel bracket that fits into a groove in the aluminum quadrent that the cable attaches to. I had some problems with that bracket moving in the groove slightly and making the TPS voltage lsightly erratic.