yet another tranny question

[lee]

OK, I'm gonna apologize in advance for the length. Not sure what's germane and what isn't, but want to get out as much info as I can to help garner potential solutions with my new problem. Also, keep in mind I live in flat-land. The only significant hills are the bridges high enough to let ocean running boats go under - somewhat steep, but not mountain grade, and not long - say 3/4 mile of climb at most.

I seem to have a transmission that slips only in 4th gear. Yes, 1, 2, & 3 currently work normally, no flare/slip. Here's the background up to this point (rebuilt tranny 22k miles ago):

a) about 15K miles ago I replaced the TPS as I always had a 2-3 flare under very light throttle - even though I never showed a trouble code on the power light. I also adjusted the bands and that didn't make the flare go away either.

b) On advice, external to a forum thread, for the 2-3 flare, about a week ago I tried moving the TPS up to a setting of as high as 0.685 volts. I have since moved it back to the original value at 0.500V (these figures are with a digital VOM). Coincidentally or not, that's the time my 4th gear slip started to appear.

The flare now seems to be gone, but I get a slip in 4th. I readjusted the bands, even tightened them enough to get the breaking effect in 1st & reverse (which should maximize 2nd & 4th band holding ability). That did NOT eliminate the slip, but in the interest of not burning up the band, I since backed it off some. OK, so here's the characteristics of the "slipping":

a) holding the car in 3 until I reach a stable, level ground speed of 45-50mph, then moving to D, results in a shift with about the right amount of feel. There is no flare in RPM, and the car continues normally.

b) going from a dead stop in D with moderate traffic flow, the car shifts fine at all appropriate points until it gets to 4th, then as it shifts, the RPMs climb to around 3K rpm whereas it would only have gone to around 2.5k rpm (with that amount of throttle) in the past.

c) trying to accelerate (at approx 1/3 throttle) in D/4th, at around 45mph, will result in a slipping of rpms up to nearly 4k rpm before the box kicks down to 3rd. Also happens when I try to maintain speed up a bridge/hill. If it slips enough to make it to ~4k rpm, there's a downshift to 3rd that "fixes" the problem for that moment.

d) I have not tried to maximize the amount of slip to see how bad it can get. Nor have I tried a stall speed test.

e) If I move off in D at a very moderate level, the system seems OK. I can gain speed on flat ground with light throttle with no slip (that I can perceive anyway). This would under conditions like when the traffic flow changed from about 50 to 55mph as the limit changed between towns.

f) when it is "slipping", I gain speed, it's just the rpm is higher than it's ever been and it "feels" like slipping is occurring - I'm basing this on to work & back conditions I've experienced since the rebuild some 22k miles ago.

g) there haven't been many opportunities, but if I give it a relatively heavy foot (just enough to avoid a downshift) the "slip" is there when it changes from 3rd to 4th - didn't really watch the speed, but I'm guessing around 50-55 mph for the 3-4 shift so you have an idea of how much throttle I'm talking about

Last point. The Power light now almost randomly gives me the 16 flashes on start-up (about every 4th time I start the car). The trouble code set is 31-TPS. I put back in my old TPS, one that never had set a code, and on the second startup, I got the flash again. Coincidence/TCU/??? There does not seem to be any other issues, i.e., with a manual downshift into 3rd I get engine breaking, etc.