Engine/Transmission (1994 - 1998) '95 Auto Trans down shifting

[WRohrer]

i am having problems with transmission gears downshifting from 4th to 3rd gears at highway speeds (55 +). Have taken to transmission shop and there does not appear to be anything wrong with the transmission. Any ideas on a fix. Also, does anyone have information on throttle adjustment cable.

 

[dalton4]

Looks like your Throttle Position Sensor (TPS) may be the problem. A search will provide plenty of info on the subject.



Jerry

 

[Joe G.]

First thing to try is contact cleaner. Radio Shack has it. Hose down the shaft area and work the linkage back and forth for a while. That will usually fix it. If it does not, then there are some wires going to the connector. Pull them free from the cable housing so they are loose. This prevents static cross talk with the TPS circuit and other circuits.



Once it's cured, dose it with contact cleaner once in a while to prevent it happening again.

 

[shendren]

don't just pull those wires loose. pull them out and back about 2 feet, wrap in black tape, put in loom and zip tie over close to the fender well... ... ... . that is the only thing that fixed my tcc from locking up... ..... i tried all of the other solutions on this board. none fixed it..... good luck.....

 

[Rnpeder]

I too have a '95 auto. Funny thing, I took it in to have the throtle cable recall performed, and after I left, the first time I let off the pedel over 60 or so mph, it threw me into the windsheild downshifting to 3rd. After 2 trips back to my quality dealer (ha), they say that nothing they did affected it, although they said they did re-adjust the cable. It still downshifts HARD anythime you let off the fuel. Don't move that foot at 90, needless to say it goes past redline. Yes, it locked and unlocked constantly before, always has from day one, but it had never acted like this. I have sprayed CANS of contact cleaner, pulle feet of wire out of the loom and nothing has helped other than learning to drive with two feet, one on the fuel slightly with the other braking. I think my next truck will be a kenworth,,,,,,

 

[Joe G.]

They messed up the TPS adjustment when they did the recall. Part of the recall is to correctly adjust the linkage so that the voltage is correct on the TPS. Obviously they didn't do it. The service manual has the procedure. Mine is not handy or I would quote it here.

 

[shendren]

TPS Adjustment

The throttle position sensor, shift lever, and throttle valve cable are critical to proper operation of the transmission. If one or more of these are out of adjustment or if the TPS is noisy, shifting will be erratic. Before performing any adjustments, check the transmission fluid level and sniff the fluid. Do not make any adjustments until the fluid level is correct, and burned fluid has been replaced.

The service manual says to adjust for 0. 8-1. 2V at idle. On many trucks, this voltage is too low, resulting in TCC chatter at moderate throttle loads. The TPS is not officially adjustable but the mounting holes are slotted and the body can be rotated slightly. Adjustment is relatively easy, and requires only a digital voltmeter and a few hand tools. A little adjustment goes a long way...

TPS wire color code:

• Black = ground

• Orange/dark blue stripe (center pin) = signal

• Purple/white stripe = 5V power

Testing and adjusting the TPS:

1. With the key "OFF", unplug the connector from the TPS.

2. Turn the key "on" and insert DVM probes into the connector to reach the connector pins. Short pieces of wire or paper clips can be used to extend the DVM probes for reaching into the connectors.

3. Read from the purple wire to the black wire (these should be the outside pins). Power should be 5V with the key "on".

4. Turn the key "off" and plug the connector back onto the TPS

5. Insert the leads from the digital volt meter into the back of the TPS connector. The DVM negative probe goes into the back of the connector cavity with the black wire. The positive DVM probe goes into the back of the connector cavity with the orange signal wire.

NOTE: Push the probes into the rear of the connector until the probe tips reach the metal connector pins.

6. Loosen the TPS mounting screws

7. With the engine off and key on: Adjust the TPS position for 1. 2 to 1. 5V on the signal wire with the throttle at the idle position - more voltage makes more TC clutch pressure, too much will set a fault code. Often, adjusting for 1. 4 to 1. 5V at idle will cure TC clutch chatter under light load conditions. NOTE: The factory setting is 1. 2V max, so proceed carefully.

8. Tighten the TPS screws, slowly open the throttle to the WOT position and then return return to idle. Watch for voltage jumps - the voltage should change smoothly from the idle value to at least 3. 5V at WOT (5 volts is all you should be able to get).