cougar

I really hate bandaiding problems, but I haven't been able to find and fix my overdrive problem. Here is the problem. If I adjust my TPS any higher than .2 volts, overdrive will not engage unless I let up on the throttle. As soon as I get back on the throttle it shifts out of OD. But the cruise control works normal. If I adjust the TPS down as low as I can without it freaking out because it is off the edge of the resister, shift is normal (kinda) but cruise control runs away.
What I have done so far:
2 different and ohmed good TPS sensors.
Tried the pot TPS delete.
3 different ecms of unknown character.
3 new VSS sensors and I tried the one off my other truck just cuz.
Checked and repaired or bypassed any questionable or bad wires and connectors.
Tried a variable resistor in the 5V line to the TPS.
Only minor changes in how it reacted, not enough to call it even close to fixed. My only remaining option is to control OD external to the ecm.

d22019

Have you changed out the od solenoid in the transmission? I had a similar problem and a new solenoid fixed it. You can change it out with out pulling the vb. Just cut the wires and solder the new one in.

cougar

The OD solenoid works as advertised when directly connected to a switch. That was one of the many things I tried during trouble shooting. The problem seems to be inside the ecm. I wish I can get a schematic for it. These brainless boxes are 20+ years old now. And I know things like capacitors and coils deteriorate with time.

j_martin

3 different ECM's with no change. You can scratch that one off.

Maybe a wiring fault between the ECM and the solenoid. I'm thinking engine rocking on the mounts with torque moving a wire.

cougar

Been through each wire, replaced a few, bypassed some connectors. The failure can be tracked to any change in the TPS adjustment which you can't adjust properly. Someone suggested a bad VSS signal to the ecm which both the OD and cruise control use. New VSS and wiring repair VSS to ecm, no effect. Maybe what we are getting for a VSS is not the correct output? I've read voltage output and I've read pulse output. Does the ecm use one and the speedo use the other? Just because all 3 ecms do the same thing doesn't exclude them from being the problem. I have no proof they are good.

KRB

So when you have it adjusted low and on cruise control it works correctly? But when adjusted high the cruise just takes off?

cougar

When I have the TPS set to 1V at ide, OD will not engage but cruise control works great. When I set the TPS for .2V OD will engage with a slight letup on the throttle, but cruise control will run away.

KRB

By run away you mean it just keeps increasing in speed?

j_martin

What's the difference between a first gen and second gen TPS? They look the same.

Adjustment should be 1.0V at idle, and 3.5V +-0.25V at WOT. If it's higher, you'd have the symptoms you describe.

ClassA4x4

One difference I know is the 2nd gen TPS rotates the other way, the throtte cable pulls the lever from the front.

patdaly

Just for giggles, could you try a resistor in the OD engage wire?

Something isn't right with the resistance values in there.

KRB

I'm having kinda similar issues with mine too. But CC works fine.

What's the VSS job in this scenario?

j_martin

Vehicle speed not dependent on gears, slippage, etc.

j_martin

Would still theoretically work, maybe swapping power and ground wires.
Back to topic. If TPS is set at 1.0 at idle, what does it read at WOT?

KRB

So is it a factor in this equation or not? Does it affect the 3-4/4-3 shifts or his cruise control?