Crazy throttle question

[HSRACER]

So I have a crazy throttle question for the group.

I have a 5.3 in a 67 stepside that came out of a 03 suburban with drive by wire. The problem that I am having is the transmission downshifts at very light pedal pressure and slight movement from the idle position.

It drives well when you give it slight pedal movement, but when driving it what I would call normal it always downshifts way to early.

After so diagnosis I have found the tps reads 100% at half the pedal stroke. I then pulled elbow off the throttle body and verified the actual throttle plate is wide open at half throttle on my pedal.

My question is can the pedal be calibrated to the throttle plate somehow? I would like to see it work with half pedal equaling half open throttle plate and so on. if it can be done is there a sequence or procedure that you can share with me.

I am just learning the whole LS drive by wire thing and have a friend who is just learning the HP tuner program. We are novices at this kind of diagnosis and repair so be gentle!

Thanks for any assistance you can give.

[ls1nova71]

I've seen this happen when a TAC from a truck with adjustable pedals is used with a standard gas pedal. Did you by chance change the pedal?

[HSRACER]

Originally Posted by ls1nova71

I've seen this happen when a TAC from a truck with adjustable pedals is used with a standard gas pedal. Did you by chance change the pedal?

I bought the truck as is so I don’t know the history. Are there any numbers I can check?
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[beaterku]

Originally Posted by ls1nova71

I've seen this happen when a TAC from a truck with adjustable pedals is used with a standard gas pedal. Did you by chance change the pedal?

What was the remedy? My LQ4 came from a denali with adjustable pedals. I am using the adjustable TAC with a standard truck pedal. Haven't finished the project yet. Curious what panned out.

[ls1nova71]

I think it needs a non adjustable pedal TAC, but not sure. My buddy never did anything about it, he just got used to driving it that way. I've driven it and it is a bit touchy, but not all that bad once you get used to it. I can look and see what the numbers are on that TAC and what they are on mine, but I don't know when he'll have his car back out again. If you get it going and it has this problem, get a hold of me and I can lend you a TAC to see if it remedies it since you're close.

[beaterku]

Originally Posted by ls1nova71

I think it needs a non adjustable pedal TAC, but not sure. My buddy never did anything about it, he just got used to driving it that way. I've driven it and it is a bit touchy, but not all that bad once you get used to it. I can look and see what the numbers are on that TAC and what they are on mine, but I don't know when he'll have his car back out again. If you get it going and it has this problem, get a hold of me and I can lend you a TAC to see if it remedies it since you're close.

So I powered up my truck last night to check wiring and noticed that I am having the same problem. My TAC came from the same donor as the engine and ECM. Its #12573059. I bought the GM truck pedal #15264643 that is for the same year Silverado 2500. I am getting full throttle when the pedal is half way down. When I look up the TAC module for a 2003 Silverado 2500 it is showing #12588923.

Were you able to figure out if it was in fact the TAC module causing the problem?

Thanks!

[beaterku]

Did some digging on ebay of all places.

Standard truck pedal and comes with #12588923
https://ebay.us/DLsWzk

Adjustable pedal and comes with #12573059
https://ebay.us/fXx2y9

Looks like this may be the solution.

[BR3W CITY]

Engine->Airflow->Electronic Throttle -> Desired Pedal Area

Take a look at that chart and see when it commands 100%

[HSRACER]

So we just tested my buddy’s 02 suburban with the tax and it performed as you would expect. 40 percent throttle equals 40 percent blade opening.

I guess I will see if there are options for different tax modules
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[BR3W CITY]

I'm sure that'll be useful for some folks in the future. I'm surprised it hasn't come up before, but I'd guess that the # of adjustable pedal GenIII trucks (high model line trucks 04-5) is low in comparison to the overall #. Guys using Denali, Escalade or high-line Yukon/Tahoe's as donors would need to keep an eye on part #'s

[ls1nova71]

I have some spare TAC modules, so if you want to try one you're welcome to it. I work downtown and get off at 8:30 in the morning if you want to meet me somewhere just let me know.

[beaterku]

Originally Posted by ls1nova71

I have some spare TAC modules, so if you want to try one you're welcome to it. I work downtown and get off at 8:30 in the morning if you want to meet me somewhere just let me know.

I’ll shoot you a PM

[HSRACER]

We ended up using hp tuner to modify the tac vs throttle position sensitivity and it worked pretty well. The hp tuner gave us a warning to not mess with this setting as the possibility to lock out the computer existed.

I figured I hated the way it worked so we might as well try it and we took baby steps going forward. We got it to a point that it seemed to work acceptable and we stopped for fear that any more modifications could screw us up.

Drives well now but I may try to see which Module I have and decide if I want to change anything.

[michael bustamante]

i have the exact set up in my 67 stepper as well! and its orange!
mines a 2003 Yukon doner with non adjustable pedals and I don't have this issue but my 13 Silverado with adjustable pedals does... downshifts everyime I step on the gas even a little. looks like im taking it in

[ls1nova71]

Originally Posted by michael bustamante

i have the exact set up in my 67 stepper as well! and its orange!
mines a 2003 Yukon doner with non adjustable pedals and I don't have this issue but my 13 Silverado with adjustable pedals does... downshifts everyime I step on the gas even a little. looks like im taking it in

Can you post a pic of your pedal and how far it moves? The 13 Silverado shifting issue probably has more to do with the transmission than the pedal, 6l80s shift weird anyway.

[BR3W CITY]

Noticed this on a dealer parts listing:

GM Part No.: 12573059
Module,Electronic Throttle Actuator Control

Part Description MODULE,ELEK THROT ACTR CONT
Replaced By 12588923

[beaterku]

Originally Posted by BR3W CITY

Noticed this on a dealer parts listing:

GM Part No.: 12573059
Module,Electronic Throttle Actuator Control

Part Description MODULE,ELEK THROT ACTR CONT
Replaced By 12588923

Well that is an interesting wrinkle...

[72GreenMonster]

Good forensic work on the dbw and TAC challenges.
It is my understanding the 99-02 TAC is also different.

I just bought a 02 gas pedal and TAC on ebay for my 02 tahoe donor 5.3.
Not quite ready to fire up but
curious if it will match up to pcm and my throttle body.

I did find this link which covers LS throttle and TAC differences. Hope it helps
and good luck to all those in TAC school.

https://www.lsenginediy.com/gm-gen-i...uipment-guide/

[LH Lead-Foot]

Using a non-scientific method, I took my HF angle gauge placed it directly over the pivot of my 2003 Tahoe electric adjustable throttle pedal. After 5 tries to get an average, I measure 12 degrees of movement of the pedal. That ain't much and surprised me a little. I would expect to have similar 5 volt signals which would make one think there is not reason to have a different TAC module. But, who knows...we didn't built it.
Seeing the video of the non-adjustable pedal, which appears to be much longer movement, perhaps twice as much. I would guess the APP sensor has major sensitivity over a very short range of motion compared to fixed pedals.

I tried to take photos with some better than others, but burry or too shiny to be worth posting, but still 12 degrees of movement.

If there a two part numbers listed for this particular RPO code w/adjustable pedals, I have no idea unless there is a first design, second design or internal electronics have change. I was told the GM changes the part number with a different supplier, materials, and even the box packaging.

But I would definitely say, there is two TAC modules. One with adjustable pedals and one without.

We have seen many use mis-matched APP sensors and TAC modules use in other builds. Some caused drivability issues, codes or did not work at all on the DBW system that are becoming more plentiful in the bone yards.

My suggestion is with cameras everywhere in phones, but get as shot of the RPO codes (Trucks / SUV's alway glove box door) but VIN as well for programming and future reference.

Newer PCM's include mileage as well, but one can make that up in a swap, but for future swaps, get the VIN and RPO codes...and matched parts.
This has been very interesting find, adding more knowledge to the forum. My personal RPO code book does not go above 2001. I will get mine and look at it soon as I hidden 6 or more in the garage. Still, very interesting...

[72GreenMonster]

Originally Posted by LH Lead-Foot

Using a non-scientific method, I took my HF angle gauge placed it directly over the pivot of my 2003 Tahoe electric adjustable throttle pedal. After 5 tries to get an average, I measure 12 degrees of movement of the pedal. That ain't much and surprised me a little. I would expect to have similar 5 volt signals which would make one think there is not reason to have a different TAC module. But, who knows...we didn't built it.
Seeing the video of the non-adjustable pedal, which appears to be much longer movement, perhaps twice as much. I would guess the APP sensor has major sensitivity over a very short range of motion compared to fixed pedals.

I tried to take photos with some better than others, but burry or too shiny to be worth posting, but still 12 degrees of movement.

If there a two part numbers listed for this particular RPO code w/adjustable pedals, I have no idea unless there is a first design, second design or internal electronics have change. I was told the GM changes the part number with a different supplier, materials, and even the box packaging.

But I would definitely say, there is two TAC modules. One with adjustable pedals and one without.

We have seen many use mis-matched APP sensors and TAC modules use in other builds. Some caused drivability issues, codes or did not work at all on the DBW system that are becoming more plentiful in the bone yards.

My suggestion is with cameras everywhere in phones, but get as shot of the RPO codes (Trucks / SUV's alway glove box door) but VIN as well for programming and future reference.

Newer PCM's include mileage as well, but one can make that up in a swap, but for future swaps, get the VIN and RPO codes...and matched parts.
This has been very interesting find, adding more knowledge to the forum. My personal RPO code book does not go above 2001. I will get mine and look at it soon as I hidden 6 or more in the garage. Still, very interesting...

Tricky, yeah yeah the challenge is between the 2 wire and 3 wire tac module along with the different pedals would love to have a simple solution for plug-and-play

[72GreenMonster]

Originally Posted by 72GreenMonster

Tricky, yeah yeah the challenge is between the 2 wire and 3 wire tac module along with the different pedals would love to have a simple solution for plug-and-play

Sorry just one yeah! Voice text error. Not yeah yeah