My 89 745T has LH 2.2. I am tuning it after installing a "built" motor, so I have changed a lot of internal and external parts and may not have it all sorted out. On deceleration sometimes, meaning when my foot is off the gas, the rpm will surge a few hundred rpm up and down. I suspect this is in the TPS (really on/off) switch. I have adjusted it so that it clicks when the throttle is opened. Could my injector cut off on deceleration be malfunctioning? How do I test this?

Thanks,

Philip Bradley
pbonsalb@juno.com

Philip-

When testing my O2 sensor, I found the only time the voltage dropped below .8 volts was after revving the motor to 2K and then releasing the thottle- the voltage would drop to .1-.3 volts just before the motor resumed idle. This voltage drop should indicate the injectors were shut down by the ECU upon seeing the TPS close at idle.

I'm assuming the O2 is bad (ie 'lazy') or my mixture is rich, but I'm going to find out with a new O2 this week.

-Dylan

An easy way to test for injector cut off is to tie into the back side of an injector plug with a low voltage light bulb. Someone acually makes these things, but I can't remember who. They are called bug lights or something. I know the ECU provides a switched ground and the power for the injectors comes through the resistor pack. You can check the throttle switch for continuity to ground with throttle closed at pins one and two. Two goes to ground on the intake manifold and is the center pin. The third pin is not used, but I think it closes at W.O.T.

HTH

bagle 87 745T