1999 Tahoe Gear Changing Problem

[executor04]

Hey all

This might be difficult for me to explain because I do not know all the proper termonology and working processes for what I am about to explain but I will try my best.

Scenario: You are at a full stop. You want to merge into a highway. You give a slow gradual push on the pedal,you move off, you push down half way and you switch gears and your rpm goes up, not that much like around 2500 or so, and you get great power.. Some guy is coming speeding 100mph behind you and you cant retreat back into on ramp so you floor the pedal, you switch gears again, the RPM goes to around 4000-5500 and you hear the engine pushing that power...

Ok thats what I believe happens to any tahoe user, as it did with my truck .. well forever..

Recently I have noticed (after It got detailed), that acceleration is fine, pushing pedal half down does switch your gear, but once you make that switch, and your hovering around 1200-2000 rpm, it will never switch to any other gears.. WHat I mean by that is, if you continue to hold your pedal half way down you continue your normal accelration. If you floor it, you STILL continue normal accleration. No real change. You don't automatically go into another gear to get that high RPM power. Its as if the pedal has no function past half way.. Regarding the detail, I don't see how this could have been a problem unless when htey were cleaning the engine something happened, or maybe something to dow ith the cable connected to the pedal, but I am open for ideas...

Thanks

[2000CAYukon]

The Throttle Position Sensor is used by the PCM (along with vehicle speed and RPM) to determine when to down shift. It is possible that they got it wet when the detailed it (did they detail the engine compartment).

The TPS is basically a potentiometer that varies resistance based on throttle position. There is a way to test it with a ohm meter. I think there are 3 wires to it. +5 reference, gnd and return. You should be able to back probe between the ground and the return and see the voltage change based on position.

It may also just dry out after a day or two and function properly again.

//2000CAYukon

[executor04]

Originally Posted by 2000CAYukon

The Throttle Position Sensor is used by the PCM (along with vehicle speed and RPM) to determine when to down shift. It is possible that they got it wet when the detailed it (did they detail the engine compartment).

The TPS is basically a potentiometer that varies resistance based on throttle position. There is a way to test it with a ohm meter. I think there are 3 wires to it. +5 reference, gnd and return. You should be able to back probe between the ground and the return and see the voltage change based on position.

It may also just dry out after a day or two and function properly again.

//2000CAYukon

Thanks for reply. The detail is now about 2 weeks old and nothing has changed. Engine was detailed yes.. I do not know much of what you just said but I will bring it up when I take my truck in for servicing. I don't know if this could mean anything but when I had some audio guys working in my truck (and it wasn't starting because of this problem I had), they were tugging on the cable for the pedal. I don't know if that could have done anything. Like I was saying, it feels like once the pedal is pushed anymore past the halfway point, it doesn't register. You get the same power at half push, vs. flooring the pedal.

Thanks

[2000CAYukon]

Originally Posted by executor04

Thanks for reply. The detail is now about 2 weeks old and nothing has changed. Engine was detailed yes.. I do not know much of what you just said but I will bring it up when I take my truck in for servicing. I don't know if this could mean anything but when I had some audio guys working in my truck (and it wasn't starting because of this problem I had), they were tugging on the cable for the pedal. I don't know if that could have done anything. Like I was saying, it feels like once the pedal is pushed anymore past the halfway point, it doesn't register. You get the same power at half push, vs. flooring the pedal.

Thanks

If they were tugging on the cable, it is possible that something when wrong. I am not sure if the cable can be adjusted or not but it should be checked along with the TPS.

When did this problem start? After the detail or after the audio guys worked on it?

//2000CAYukon

[executor04]

Originally Posted by 2000CAYukon

If they were tugging on the cable, it is possible that something when wrong. I am not sure if the cable can be adjusted or not but it should be checked along with the TPS.

When did this problem start? After the detail or after the audio guys worked on it?

//2000CAYukon

I noticed it after the detail. It IS possible it might have been caused from that cable incident, but I am still pretty sure there were no visible problems until after the detail. Ill give a 90% chance it was after detail. But its just the weirdest feeling. If you floor your pedal, you know the kind of power you get... for me, flooring the pedal, and pushing it around, or a little before half = the same thing. Like if you hit the pedal half way down, that level of acceleration, does not change, even if you floor it, you still continue to acclerate within a normal rate within the same gear. I'll have them check the cable too, but its just so weird because it drives normally, no problems.. its just like the pedal doesn't work past half way...

[2000CAYukon]

Originally Posted by executor04

I noticed it after the detail. It IS possible it might have been caused from that cable incident, but I am still pretty sure there were no visible problems until after the detail. Ill give a 90% chance it was after detail. But its just the weirdest feeling. If you floor your pedal, you know the kind of power you get... for me, flooring the pedal, and pushing it around, or a little before half = the same thing. Like if you hit the pedal half way down, that level of acceleration, does not change, even if you floor it, you still continue to acclerate within a normal rate within the same gear. I'll have them check the cable too, but its just so weird because it drives normally, no problems.. its just like the pedal doesn't work past half way...

Have a helper sit in the driver seat without the engine running and have them push the gas pedal all the way down. At this point, you should not be able to open the throttle any more by hand. If it moves, the cable may have come off the track and is not opening the throttle all the way.

//2000CAYukon