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Discussion Starter #1 (Edited by Moderator)
I have a freshly rebuilt (3,000 miles) 4L80 behind my "new" 6.5L in my 1995 Chevy Step Van motorhome conversion. Engine and transmission both run great.


I drive >90% on highway at almost WOT. My only complaint is that when I "floor it" while cruising at 70mph to pass, or when I hit a hill, it jumps down into passing gear too easily.


I have the TPS adjusted properly. I figure if I adjust it counter-clockwise to minimize voltage at idle (0.5V? I forget exact number), then the high speed voltage is also minimized. I assume when the computer senses high voltage from TPS, it is thinking I need passing gear. So, I try to keep it adjusted counter clockwise to keep the WOT voltage low. However, if you go too far, you get a Code 22 (low TPS voltage at idle).
Turning idle speed up a bit helped this, but I just need to take a little sensitivity off the passing gear kick-down. When I had Code 22, it would not kick-down at all and I liked it - could keep pedal mashed without kick-down - however, it also keeps TC from locking up and fluid temp got very high.


So - how to "trick" the TPS into sending lower voltage at WOT, but not at idle? OR - do I have this all wrong?

OR - is there a wire I could tap into to put in a switch to disable kickdown? Would that affect normal downshift (like when slowing down)?
 

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The computer controls the shifting of gears, so in order to adjust shifting in anyway you need to adjust the shift points with a tune or something similar.

If I understand you right, you run at WOT and you think it goes to passing gear to easily? why are you running at such high rpm? how fast are you going? With a 4.10 rear end, i'm at 2000 rpm at 60mph.

The TPS is used by the computer to see when it needs to go to passing gear- a sudden WOT hit to the gas pedal triggers it to shift to passing gear. If you are running/cruising at wot and you need a little boost up a hill or something the computer will not know the difference between needing passing gear and your cruising.

Again, something seems wrong. Are you not getting into 4th? in 3rd gear with TCC lockup my RPM is at 3000 at 60 mph.
 

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Discussion Starter #3 (Edited)
I am not really running at WOT all the time on level ground. No tach. I'd say though at least 7/8th throttle to cruise at 75 mph in 4th. If I press it to floor suddenly from there, it will kick down. OR - if I come to a hill and truck starts to slow - it will kick down. I believe all is well and running as supposed to- just not to my liking. I believe the computer (which controls ONLY the transmission) looks at voltage from TPS to guess my intentions (to go fast) and compares to speed sensor. I want to reduce voltage to computer if possible (I think).


Yes, it could possibly be reprogramed to accept a higher voltage, but I wouldn't know how to do that. Maybe vehicle was never designed to cruise over 75?


My high profile vehicle is VERY sensitive to air turbulence. I can go 85 in heavy traffic, but barely 73 sometimes on flat calm days.
 

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so you have a standalone controller?
 

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So just to verify, it is the stock computer in the factory location and the factory harnesses?
 

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Discussion Starter #7 (Edited)
So just to verify, it is the stock computer in the factory location and the factory harnesses?

YES, correct.


I might add that I had old tranny rebuilt when I replaced engine last year. Before that, it mostly ran so that it would never kick-down into passing gear. One day, it started suddenly to have a passing gear. That would last until next trip then mysteriously disappear. It would come back from time to time. It behaved EXACTLY like it does now with new engine and rebuilt tranny. I did not like it then when it would happen because downshift was too sensitive.


Most of the time it would not kick-down (for long periods - weeks or months), and if I actually needed it, I could do it manually (4th to 3rd). With my new engine and rebuilt tranny, I initially had TPS set wrong, and it had no passing gear, and showed code 22. Now, I know it probably used to run for long periods with code 22 (which doesn't show a light). However, that also keeps TC unlocked, and it runs very hot (I thought the heat was normal back then). It runs much cooler now. I added a temp sensor on outlet line when I swapped.

BUT - it is still too sensitive for my liking. I actually think it is 100% normal - I just want to change it. I can actually "feel" when it's just about to downshift and let up slightly, but my son is completely lost when he tries to go above 70.
 

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If you are in fact running at WOT there is something wrong. You need to get a tachometer and see whats going on.
 

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Discussion Starter #9
Why do you think something is wrong? Seems like 80mph at WOT is faster than originally designed for a fully-loaded delivery van with high wind resistance. How fast should it go flat out? Seems to run great except that annoying passing gear.


If I get a tach, what will that tell me, other than my rpm?
 

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Discussion Starter #10
I realized that I did not actually mean I was cruising at WOT. On flat ground, with no traffic, smooth road, and no head-wind, I can cruise about 72-75mph with about 7/8ths pedal. However, when I floor it to pass, or compensate for a hill, it kicks down and I can actually lose momentum/speed rather than gaining speed with extra throttle.


On my 500 mile round trip last weekend, truck seemed less prone than usual to do this. In fact, a couple times, it mysteriously didn't do it, but at those times I was really moving (80mph), and perhaps was closer to WOT, so that the increased throttle by flooring it did not kickdown.


The bit of extra speed may have come from replacing the fuel pump? Or maybe that road was just extra smooth.


Truck (Step Van) is VERY sensitive to air turbulence. Easily get 10 mph in traffic compared to pushing still air. The "bow wave" from passing (or trying to pass) a semi can be frustrating.
 

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If you lose power after a downshift, the engine is not healthy. My 1982 6.2L would behave like that when the injection pump was failing. Put a new pump on, and it makes good power all the way to redline.


I would think you should be able to hold 80+ MPH even in that truck with a healthy 6.5L. I've pushed my squarebody to 105+ MPH and it was still pulling, and those are pretty bad aerodynamically too.


When my last pump was going out, I had the truck dynoed, and it was making 62 HP at the rear wheels. That's less than half the rating of the engine, and the 6.5L is rated more still. I bet you're down on power for some reason, and that is your root problem. A downshift should never result in LESS acceleration.
 

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Discussion Starter #12 (Edited)
I think I'm not explaining it well. After thinking about it, when it kicks down, it does pick-up, but I think I'm hesitant to let it rev that high and I let off the pedal. This causes it to up-shift and then I try to give it a little more and cycle repeats.


I don't think anything is "wrong". I can't imagine doing 100mph, or that it was designed for that. I need to get it weighed. Fully-loaded, I have 50 gallons of water, three motorcycles, two persons (including my own 270lbs). Generator, 15 gallons of gasoline, lots of tools, big cooler full of food, beer, and ice.....


Is your 105+ turbo? Mine is NA. Dually, of course. Windows and wing vents open. Don't recall ever getting passed by UPS, Fed-Ex, or bread trucks ever in my life. Not sure they can go that fast.



Also, We "think" I have a lowered compression Marine engine.


80 if my personal speed limit, I don't feel safe over that. Afraid that big flat windshield is going to pop out and hit me in the face.



ANYHOW - My original question is still unanswered - regardless of whether or not my truck is running at optimum - Is is possible to make the passing gear less sensitive?



As I may have mentioned, when I had a code 22 (no passing gear, but no TC lock), I sort of liked it - up to a point. A middle ground would be perfect.
 

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I am not familiar with the factory controls on the early 4L80E with the 6.5. I know on the gas motors, you can reprogram the computer to have it shift however you want. In your case, you might have to switch to an aftermarket transmission controller, which is expensive, but will do what you want.


I recommend you look into what tuning is available for the 6.5 controller, and have it tuned if possible. If not, look into aftermarket transmission computers.


My 6.2L is naturally aspirated, but it is not a dually. 105 MPH is sketchy, which is why I called it quits. It would do more, but I didn't feel safe, even in the middle of nowhere with no one else on the road. But it did have the power for it. Yours sure has some weight to haul around, but the weight only means it gets to top speed slower. The top speed is when the engine power can't overcome the air resistance. I still think yours should be able to do 80 MPH without drafting.


I wouldn't personally be afraid to let it downshift and rev out for a while, especially if it is just now and then (hills, short highway sections). I understand not wanting to have it redlined for hours on end, as that does shorten the lifespan of the engine and is just unpleasant to listen to on a long trip. But if you can't tune the stock computer, you have to decide if the cost and complexity of an aftermarket transmission controller is worth it vs. just letting it rev out now and again.
 

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The control sector of the computer should be the same for the gas and diesel, so a tune should work for you.
 

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It's not unless you have a special controller and a tune...
 

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Its pretty easy to change in tuner pro. get yourself a programmer and change it yourself :) I personally really hated the stock shift patterns so I changed them all, I found it willing to downshift so incredibly easily, and I live in the parries ! tuner pro will let you completely change all the shift points
 

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It can be made to work as you would like it.

Just keep plugging at it.
 

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Discussion Starter #19
UPDATE:
Well, I did nothing, but eventually it got better on it's own. Runs great now. I can cruise at 75-80 and still get passing gear only when I want, or come to a hill, etc. Maybe the computer had to "learn"? Or, maybe some loose connection fixed itself?
 
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