Thottle Position Sensor

[akeller]

I have a 1993 GMC 1/2 ton with a 6.2 L. A year ago I replaced the injection pump. At the time the garage had trouble with the TPS so they replaced it. They then calibrated it and it was fine. A month later the Service ebgine soon light came on and the truck was shifting rough (You had to step on it make it shift) and it wouldn't shift into O/D. I then took it to the garage and they adjusted it again. Its been good up to a month ago. Now the Service engine soon light will go on and it shift rough, turn it off and the next day its fine. It has done it 3 times over the past month. Any suggestions ? Is this normal ? Is there a problem with the new TPS ?

[BobND]

Those sensors can be problematic. It would not surprise me if the new one has gone bad.

You can monitor the voltage on the center terminal with a voltmeter by tapping into the wire , and see what's really going on.

[More Power]

When measured between the blue & black TPS wires, you should see .5-.75 volts at idle and 4.2-4.5 volts at wide open throttle. The computer supplies a regulated 5 vdc to the gray wire.

When monitoring the blue & black wires, you should also see a smooth varying voltage as you move the accel pedal through its range. Erratic voltages or dead spots while moving the pedal would indicate a problem with the TPS.

Jim

[dieseldummy]

I've had similar problems off and on with my '93. Usually all it requires is loosening the bolts on the sensor and moving it back and forth through it's range and then re-adjusting it to voltage specs. I figure if I can keep it going like that then I have been saving $120...

I assume that you have the 4L80E? One thing that concerns me is that the SES light is coming on. When my TPS gets out of adjustment it just wont shift into OD, the only time the SES came on is when I lost the input sensor and it picked it up as slip. When it does that it will only shift into 2nd gear.

[BobND]

I had a 1993, with a 4L60. I had to replace the TPS twice because of the SES light coming on.

IIRC(it's been a while), it would throw a code for EGR, as the emissions 'puter was looking at the TPS to help it modulate the EGR valve.