Crazy throttle question
 

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.

Re: Crazy throttle question
 

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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Re: Crazy throttle question
 

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

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

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

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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Re: Crazy throttle question
 

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!

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

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

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

I’ll shoot you a PM

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

Based on your pictures I have the pedal assembly with your 12588923 number.
I don’t know which module it is paired with but will have to check it out.

Re: Crazy throttle question
 

The pedal that came with my engine was the adjustable with 12573059 TAC module. I switched to a standard truck pedal and am getting the half throttle issue. LS1Nova71 is local to me and has graciously offered a 12588923 module to test to see if that fixes the problem. Will report back once I test.

Re: Crazy throttle question
 

Interesting problem. I have adjustable pedals from the power train donor, but all of the modules / sensors are matched.
Just wondering, is a difference in travel at the pivot where the sensor mounts, on non-adjustable pedals (Fixed) and the adjustable pedals. Otherwise, there is no other reason for the change in part numbers. A call to a friendly Chevy dealer part counter may ask if it has adjustable or fixed pedals by using the RPO code, as it would show up on their screen as a prompt.
My old parts manager took a counter job at a large GM dealer after our old dealer went thru a bad "Buy-Sell" issue...and we closed. I will stop in and ask since I have an appointment near by.
Of course, we can alway check RockAuto for foot notes if multiples are offered.

Yep, I am 6'4" and the wife is 5'7"...I think see wants to drive my 67 C10. So adjustable pedal are going in along with power buckets. She can drive it once.

Re: Crazy throttle question
 

The adjustable pedal has half the range of rotation of the non adjustable. I noticed it a few months back but didn’t think anything of it. I figured the sensor was calibrated differently. Guess I was wrong lol

Re: Crazy throttle question
 

Ok, so I have come up with some interesting info. I started by checking a 2003 6.0 truck we have at work, then checked a buddy's 2004 with a 5.3 and they both showed 100% on the scanner with the pedal floored, however, the pedal floored is stopped by the carpet/rubber floor mat in the trucks. I could get my finger behind the pedal where it would contact the back part (the part that bolts to the firewall) on both of them with the scanner showing 100% throttle. This leads me to believe that it is normal for them to work this way. I had originally thought the TACs were different because on my buddy's car it originally had the adjustable pedal and with that pedal it goes 100% with the pedal touching the back part. Makes sense because the adjustable pedal doesn't hit the floor covering at all. I think the touchieness of his car, and probably others, is due to the fact that the pedal has been cut down to fit better, but what that does is removes some of the leverage the stock pedal has, meaning where as you would have to move the end of the pedal, say 3 inches in stock form to get full travel, when cut way down, it is only 1 1/2 inches now, if that makes sense? Nick, you're still welcome to try my TAC, but I think it's going to be exactly the same, so I would mount the pedal and get the carpet in it and see if the carpet will physically stop the pedal at the half way mark like on the donor trucks.

Re: Crazy throttle question
 

Here is a little video of the pedal travel. At 100% throttle, I am about 2 inches from the carpet. I compared this to a neighbors nova with a 5.3 swap that came with a non adjustable pedal and he hits 100% throttle at the carpet. His TAC is buried under the dash so we couldn't pull the part number off of it. It's just the weirdest thing.

Re: Crazy throttle question
 

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

Re: Crazy throttle question
 

I'm not sure about the nova without seeing the pedal, but on the two factory trucks I checked the pedal wasn't able to go that far down. I'll have to try and find another truck to look at.

Re: Crazy throttle question
 

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.

Re: Crazy throttle question
 

His pedal is the same part number I am using. #15264643 from a 2003 2500 Silverado. I’m still convinced they are different. Why would they have 2 different TAC part numbers for the same year. Maybe I am overthinking it.

Re: Crazy throttle question
 

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

Re: Crazy throttle question
 

Well that is an interesting wrinkle...