No Power. Transmission Problem?

[mp88]

Ok, this is the biggest annoyance I've had with this truck yet. I have a 94 XLT 4x4. Changed the transmission fluid around 4,000 miles ago. The fluid is a stable red color and not low.

A while ago while I had a mattress on the roof, the check engine light came on while I was going up a hill. Every so often when I have the engine under what I'd like to call strain (accelerating at the bottom of a gear) nothing happens. I gain no speed. Even downshifting does nothing but rev and keep me at the same speed.

If I keep it strained, especially on a long highway going uphill, I sort of lose 4th gear. I can definitely tell that it has shifted from 3rd to 4th (I have downshifted into drive to confirm this) but it stays revved. About 500rpm higher than it should be. Then the check engine light comes on.
For example:
Normal highway driving: 65mph at 1900rpm.
Screwed up driving: 65mph at 2400rpm.

Does this sound like something simple such as a solenoid? Or is it time to ride this Exploder until it dies?

Thanks.

 

[Glacier991]

And what code are you getting when you read the codes as indicated by the Check Engine light?

 

[mp88]

I ran up to Advance to get my codes (since they do it for free) and got these:

KOER Code 336
EGR PFE/DPFE Volts
Out of Range
Higher than expected

Haynes Manual definition - EGR circut higher than expected

and

KOER Code 167
TP Sensor Change
Insufficient
Dyn Response Test

Haynes definition - Insufficient Throttle Position Sensor change during Dynamic Response Check

If I was a guessing man it sounds like the second code has more of an impact...despite that it says nothing about the transmission I have a feeling I'm in the wrong part of this forum. Nonetheless, any guesses?

 

[Glacier991]

4th gear is actually the application of the OD band by the OD servo. This is commanded via a solenoid controlled by the computer. Your solenoid could be weak, your servo could be a leaker when hot, or the band could be a problem.

I have 227K on my A4LD and make regular long uphills (7000 feet elev gain in about 80 miles). On the steep sections I do not use OD. I have found OD in steep terrain in an OLD A4LD will cause OD band slipping and overheat the tranny. That was about 75,000 miles ago. I suggest you take it easy on yours if your miles are high.

You might try a VB rebuild and replace the solenoids, they are cheap in the A4LD.

 

[BrooklynBay]

The first thing I thought of when you described the problem was the TPS. I see that it is one the codes. The DPFE has also been known to cause problems. They are very sensitive to moisture.

 

[mp88]

Please excuse my lack of acronym knowledge. What is a DPFE?
About the TPS'...is it common for them to go bad or would I be safe enough getting one from a junkyard (I'm kinda broke ).

 

[BrooklynBay]

Don't buy sensors in a junk yard. This thread should help you understand the function of the DPFE sensor: http://www.explorerforum.com/forums/showthread.php?t=164517

 

[mp88]

Ok, I'll take that into a big thought. Thanks a lot guys. I'm going to try replacing those parts and update this once I'm done.