TPS check procedure
The TPS controls the 3-4, 4-3 shift. It is mounted on the injector pump, towards the front of the AFC housing. It has a black connector with 3 wires.
The TPS can prevent the upshift into OD. Also the speed sensor on the tranny can do the same thing if it is hooped.
First thing to do, check your speed sensor connection.
Second thing I'd do is test the TPS.. here's the process I've used successfully before.
TPS ADJUSTMENT....
The TPS has a 3 wire connector on the top, engine side.
The center wire is orange I believe.
Under the TPS body, is a shaft that protrudes downward. The shaft has a hex head end that fits into a 'female' hex socket.
This shaft is lightly spring loaded.
Right near the top of the shaft were it first comes out of the TPS body, are two "flats" were you put your open end wrench to adjust.
You'll need a DC Voltmeter, as safety pin, or paperclip with the end slightly sharpened, and a combo wrench. I think its a 7/16" or 1/2".
Slip the safety pin or paperclip into the 'socket' part were the center wire comes out of until it makes connection with the metal jacket inside.
Connect the "+" probe of your DCVM to this.
Connect the "-" probe of your voltmeter to the "-" terminal on the battery (it's just convenient)
Turn on the Ign. key (do not start truck) and check the "at rest voltage".
It should range between .7 VDC and 1.25 VDC. (make a note of the reading for reference.)
Next, slowly cycle the throttle smoothly to WOT and watch the meter.
It should increase smoothly with no jumps or spasms/twitching.
If it does, the TPS is still working ok, if not you've got a dirty one or its failing.
I believe the total increase (above "at rest voltage") should be about 2.75 VDC.
Now, you need to go back to that shaft coming out from under the TPS.
Use the wrench to adjust the voltage SLIGHTLY!
Start with .2 VDC to begin with.
Increasing voltage will cause the 3-4 shift to happen LATER.
Decreasing voltage causes the shift to happen sooner.
I found that there was a point were the shift happened later, but also tended to cause the downshift (4-3) to be a bit touchy too, so you need to adjust a BIT and drive each time.
When you do your test drive try to use the same throttle pressure/RPM for each, that way you'll know what effect you had with the adjustment. I did a "medium" throttle (1600 RPM) and a WOT test each time.
Before I had the tranny work done mine ran just fine at about .7 VDC - .8 VDC "at rest".
Last thing to ckeck... make sure that your TV cable returns properly. The lever on the trans. case should move all the way forward with the truck off/idle. I had to add a "universal" throttle spring to be sure that happened, otherwise the line pressure(s) at idle are already increased above what they are supposed to be at idle.
The TPS can prevent the upshift into OD. Also the speed sensor on the tranny can do the same thing if it is hooped.
First thing to do, check your speed sensor connection.
Second thing I'd do is test the TPS.. here's the process I've used successfully before.
TPS ADJUSTMENT....
The TPS has a 3 wire connector on the top, engine side.
The center wire is orange I believe.
Under the TPS body, is a shaft that protrudes downward. The shaft has a hex head end that fits into a 'female' hex socket.
This shaft is lightly spring loaded.
Right near the top of the shaft were it first comes out of the TPS body, are two "flats" were you put your open end wrench to adjust.
You'll need a DC Voltmeter, as safety pin, or paperclip with the end slightly sharpened, and a combo wrench. I think its a 7/16" or 1/2".
Slip the safety pin or paperclip into the 'socket' part were the center wire comes out of until it makes connection with the metal jacket inside.
Connect the "+" probe of your DCVM to this.
Connect the "-" probe of your voltmeter to the "-" terminal on the battery (it's just convenient)
Turn on the Ign. key (do not start truck) and check the "at rest voltage".
It should range between .7 VDC and 1.25 VDC. (make a note of the reading for reference.)
Next, slowly cycle the throttle smoothly to WOT and watch the meter.
It should increase smoothly with no jumps or spasms/twitching.
If it does, the TPS is still working ok, if not you've got a dirty one or its failing.
I believe the total increase (above "at rest voltage") should be about 2.75 VDC.
Now, you need to go back to that shaft coming out from under the TPS.
Use the wrench to adjust the voltage SLIGHTLY!
Start with .2 VDC to begin with.
Increasing voltage will cause the 3-4 shift to happen LATER.
Decreasing voltage causes the shift to happen sooner.
I found that there was a point were the shift happened later, but also tended to cause the downshift (4-3) to be a bit touchy too, so you need to adjust a BIT and drive each time.
When you do your test drive try to use the same throttle pressure/RPM for each, that way you'll know what effect you had with the adjustment. I did a "medium" throttle (1600 RPM) and a WOT test each time.
Before I had the tranny work done mine ran just fine at about .7 VDC - .8 VDC "at rest".
Last thing to ckeck... make sure that your TV cable returns properly. The lever on the trans. case should move all the way forward with the truck off/idle. I had to add a "universal" throttle spring to be sure that happened, otherwise the line pressure(s) at idle are already increased above what they are supposed to be at idle.