'89 Chevy L05 diagnostics

[fjm719]

In my continued pursuit of regaining fuel economy, I next pursued what appeared to me as a range problem with the Throttle Position Sensor.

On my throttle body, the throttle range lower limit is set by a factory sealed adjustment screw. The throttle range higher limit is set my the throttle touching a boss on the casting of the throttle body. I’ve confirmed that accelerator pedal mechanism and the cruise control actuator do not further limit the range.

By generating logs with TunerPro RT, I observed that the signal from my vehicle’s throttle position sensor (TPS) is smooth and responsive. However, using the LD ADX file, I see that is ranges from 5.1% at idle, to approximately 77% at wide open throttle. Using the HD ADX file, it ranges from 0.71 volts at idle to 3.7 volts at wide open throttle.

Do any forum members know whether these deadbands at the bottom and top of the range are typical? Is there a parameter in the ECM that addresses the deadbands? Put differently, is it possible that the ECM fails to understand that 3.7volts corresponds to wide open throttle? Is there any way to ensure that the ECM understands that only 45.5% of the 0-5V TPS band represents a 100% of the throttle’s range?

Any thoughts would be much appreciated!

[MO LS Noobie]

First I would measure the actual signal at the PCM with a DVOM. Confirm that what you are seeing on the scanner is accurate. then you know what what direction to go-low signal (TPS or wiring) or PCM or PCM grounds.