Shift Point Issues and power problems

I've been researching the issue with my Jeep for a little while now and I'm hoping someone's had the same problem or can steer me in the right direction.

So, PROBLEM:
The tranny doesn't shift at the same points it used to and I have a power loss which translates into a loss of miles/gallon. First, second, and third shift higher than they used to ( all above 2K rpm and higher). It won't shift into 4th until I'm doing 49MPH, and only 49 MPH. The transmission also doesn't downshift unless I use the shifter manually to put it into 3rd or lower.

I've already replaced the TPS, and being a 2000 it's not an adjustable TPS so I'm pretty sure that's not the issue.
I have a check engine light and I'm seriously thinking about getting a set of solenoids and throwing them in along with a fluid change.

Also, the fluid is at the correct level, and It's only got about 8 or 10 thousand miles on this fluid in it.

All of the shifts are strong and I'm not really concerned with the tranny having a problem, because it never slips and all the shifts are strong. The shifter doesn't get warm, which I've had happenbefore on other cars from trans overheating.
I'm probably going to check the resistances per that one article online about the voltages fromthe TCU controller or whatever under the dash/glovebox.

The jeep is an 2000 with the 4.0L engine. I have 4.5" lift and 30 inch tires but Idon't think that stuff matters. If anyone has insight or has had this problem and knows which direction I need to go that would be great.

Thanks.

Sooooo...

Whats the code associated with your CEL?

I've disconnected the battery a few times in hopes of getting the light to go off and comeback on again so I can have it read, but the light won't go off. I thought that disconnecting would reset the cpu but it hasn't. It was reading a bad TPS before I changed it.

Your symptoms still kinda sound like a bad TPS. Have you cleared the code with an OBDII code reader. If it's still coming back, you may have a wiring problem to the TPS. A bad ground at the TPS is not unheard of. Get a meter and check the ground at the TPS and that the voltages look right.

Checking the resistance of the solenoid won't hurt, but they sound like they're ok if it's shifting firmly and hitting all the gears. A new set is pretty expensive, btw. I doubt the shifter would ever get warm since it's connected by a cable instead of directly connected to the tranny.

You sure you're not just down on power and applying more throttle, which would tell the tranny computer to shifter at a higher rpm?

I can check the wiring to the TPS.
I'm pretty sure it's not down on power, it doesn't feel any different than it did before. This light and issue came up on a road trip I took a few months ago, and there was no power difference then...only the mpg loss and shifting changes.
There's a new TPS on there, but I'll go out with the VM and check.

Thought I'd update if anyone searches this thread.

Went to Advanced and they couldn't reset the CEL, the guy there said it was the first time he had seen that happen.
Anyone have experience with that?
I did read the Chilton's and it said to reset the TV linkage. Very easy process and I think it adjusted the throttle cable a bit. I got some power from it I think and I know that I got a large mpg increase. I should be up to almost 20 mpg on a flat road now which is fine.
No dice on my shifting issue yet, I'm going to try to reset the CEL and wait for it to come back on again.

Have you plugged a computer into it to see whats CAUSING the CEL?

It's a code for high voltage from the TPS, which was the code before I changed the TPS. So I think the ecu needs help removing the code.

kf_chris said:

Thought I'd update if anyone searches this thread.

Went to Advanced and they couldn't reset the CEL, the guy there said it was the first time he had seen that happen.

Click to expand...

Yeah, I've seen Advance Auto employees be very clueless before. If it won;t clear then the fault is still present. I'd check the TPS voltages, particularly the ground. You might need to trace it back and check the voltage at the computer as well.

Get a volt meter in there and check the voltage to the TPS. Should be 5 volts (I think the OBD-II is the same voltage as the Renix and OBD-I) but check the FSM for the proper voltage. If it is high, it is either a shorted set of wires in the harness crossing a 12 volt wire over the 5 volt wire, or a bad computer 5 volt power supply on the PCM (computer) that is putting out too much volatge. Or a bad TPS ground and 12 volt wire crossed over the ground side of the TPS. Time to get out that dusty old multimeter, DVM.

So if it's a wire fix...are the harnesses available or do I have to rewire it?

Wire it yourself. It's not uncommon to need to run a new ground wire from the sensor to a bolt on the engine somewhere.