Engine/Transmission (1994 - 1998) Auto upshift - TPS adjustment?

[Vaughn MacKenzie]

I had the auto in my '98 serviced yesterday and asked the shop about adjusting the upshift so it isn't doing it so quickly. When I take of lightly it's in 3rd by 20mph. The tech claims I can have it flashed by the dealer because there were many complaints about it and that's the fix.



What doesn't make sense to me was I thought this trans was all hydraulic except for OD, so how would flashing it help? Wouldn't it require tweaking the valve body??



Here is another item I ran across in TDR Issue 49 page 20 that Howard Durand sent in. I don't know if this correalates with auto trans upshifting or not.



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[CSchafer]

The tps will only controls the shift into overdrive and TC lockup. On the Rh trans I know the other gears are controled by the tv cable hooked to your throttle linkage. On the RE I've been told it's the same way. With the truck off find the tv cable and pull it out a little bit and put a small zip-tie on it to give it a false stop. If this does what you want then adjust the cable accordanly. Hopefully that trick works on the RE as I havent done it to one but I'm sure someone will chime in.

 

[Joe G.]

Do a search for a thread started by ridesamule that has a lot of discussion with him and Howard Durand. I think the name of it is "TPS myth" or something like that. You can adjust the OD and lockup to happen at any speed you want. Ridesamule has a '96 (47RE) and Howard has a '94(47RH).

 

[Howard Durand]

The above drawing, that was printed in the TDR, is a bit different from the description. It doesn't show the filter capacitors. They may or may not be needed in all applications. My 94 seems to get along fine without them.



Adding the variable resistance to the ground circuit helped get the shift point up some but was still not what I was looking for.

Ridesamule's idea of replacing the TPS with a manually controlled potentiometer is much better as far as I am concerned.

With the resistance combination that I am using, I can get the OD shift point as high as 47 mph.

At that setting, TPS voltage is 2. 47 volts and TC lockup occurs at about 51 mph. This is a bit too soon for my liking so I keep the TC blocked until about 55 mph.

One drawback to this scheme is the loss of kickdown capability. Most likely due to the unchanging TPS signal voltage. To offset this, I have a dimmer switch wired to open the TC control circuit when needed.

The problem with most of these ideas is the modifications to the original circuit that are required to be able to try them out.

 

[Vaughn MacKenzie]

Thank you all for your input. My OD shifts in at around 42-44 as I recall and yes it would be nice to increase the speed. Maybe if I add the potentiometer as well as doing this so-called flash it might do the trick. I don't want to lose downshift ability. Now when you raise the TPS voltage does it raise or lower the MPH that it shifts into OD?



Regarding the original question about normal 1-2-3 upshift I like your trick CShafer, I'll give it a try. I am more annoyed with 1-2-3 upshift than the OD & lockup function.



Other than the shift points my truck's automatic function is good- I don't have the erratic OD shifting issues some have. My only other gripe is sometimes when I don;t come to a dead stop the truck tries to take off in 2nd or 3rd gear, even if I slow clear down to 2mph. The trans shop supposedly tested my truck for this and said it was working normally.



The shop said the trans is in great shape, fluid was clean and no residue in the pan at all. It's the original with 154,000 mi and the previous owner put about 20,000 miles on the truck towing a 28' 5th wheel.



Vaughn

 

[CSchafer]

putting more tension on the tv cable will also cure your starting in second or third gear. You will be telling the trans that you have your foot down farther. That will make it downshift and also raise pressures in the trans(might shift a little firmer also)

 

[Howard Durand]

Vaughn,



If your transmission consistantly shifts into OD in the 40+ mph range, you really don't need to mess with the TPS.



The only transmission I am familiar with is my 47RH and my modifications may not be useful in the 98.

If left alone, mine shifts into OD low in the 30 mph range which is not good for towing. Especially when TC locks up very shortly after that.

Replacing the TPS with a potentiometer allows a set signal voltage to be applied to the PCM instead of the constantly changing voltage from the TPS.

With this configuration, adjusting the signal voltage upward causes the shift into OD to occur at a higher vehicle speed.



If you use a potentiometer in the ground leg of the TPS, like it shows in the diagram, you can control the initial closed throttle TPS signal voltage.

Voltage output still changes as the throttle is advanced and you don't lose the downshift capability. This worked fairly well to delay the OD shift but the PCM still seemed to have a mind of it's own. That is why I like the replacement method. It is much more dependable. I don't mind losing the automatic kickdown.

Right now I am using the dimmer switch to unlock the TC when a downshift appears to be in order.

Our trip back to Wyoming this spring will tell me how well I really like the scheme.