'03 sub 5.3 in swap car with matching TAC and pedal. While watching LM2 logger TP % fluctuates at constant part throttle and If I go WOT sometimes it will drop to 6-8% or 0 sometimes when I start car it will only idle. So do I change pedal or TAC or could it be in the tune? I'm using HPtuners myself and new to tuning.

 

no body has any experiences or thoughts on this?

 

Send Jim_PA a PM and ask him if he has any ideas

 

Did you pull the parts yourself from the same vehicle? I've found that yards can be somewhat unreliable, and in my experience, they go by the book as to what is supposed to work with each year/model, but you may have ended up with a tac or pedal that's supposed to work together, but really doesn't.

If you did all the pulling yourself, how about the harness from the pedal to tac module? If you made your own, make sure you wired it correctly, because they are not direct Pin A -> Pin A connections. Several of them are swapped around.

How about the engine harness? I left all the factory grounds in place, removing the ones that went to sensors that I didn't use.

If you start up your logger without actually starting the engine, what's it say for TP% at dead rest? Then just very slowly apply throttle and see how it reacts and how far you go before you hit 100%

The only other thing I have read through my own research is that the TAC module needs to be powered on either at the same time, or before the PCM gets power. It will throw everything out of whack if you power up the TAC module after the PCM is up and looking for the TAC.

You could also check the connector up at the throttle body. Go over each wire carefully up there, tugging and prodding each one, making sure none of the terminal wires are loose or partially broken.

 

Ok Thanks. The car has been running for about a month now and the TP problem is something that has developed. The first time it acted up I started the car and it would just idle. Shut it off restart and it was fine. It did that a couple of times then it started fluctuating while driving down low stretches of road at steady throttle and at WOT will randomly drop to under 20% until throttle is released and reapplied. This started about the same time the trans went out and I changed it. After changing the trans it wouldn't always start right like low bat power. I would mess with the disconnect switch and it would start. A couple of days ago I changed the disconnect switch (4post) one of the small terminals was over heated internally, new switch and it fires right up. I thought that would fix driveablity issue too but it didn't. I don't have a spare TAC and pedal of my own to try but a buddy of mine has an '05 2wd trail blazer ss parts truck that I can try. My PCM is from an '03 suburban so would that work or do I need something different? What will work?

 

I bet I have replaced over 50 ETC T-Body's in the last 2 years. I have a stack of old ones. 90% of the time they get replace for a TPS DTC or 2. The main DTC that we see is P2135.
P2135 = a T-Body 99% of the time

 

Did you do a full scan for codes?

 

Thanks for the input guys. Im a heat and air contractor in a vacation community so I've been extremely busy the last week. You guys have givin me some great direction to start looking. Im a mechanical/cut and weld kind of guy, anything I can see is not a problem for me but I get a little lost on some of the electronics.

 

i drove it tonight and didn't compare the two (my *** is tired) but I did check for codes related to TP and nothing that looked suspicious (no P2135)

I played with the throttle with engine off and idle was 21% and 100% came in around 1/2 or so travel which is fine with me as it's not too aggressive feeling. With the car running and driving around 30-35% it will fluctuate 5% or so at cruise. At Wot it will kill the tires at 100% then go to 16% which is idle when running. At aggressive throttle 80-90% it will throttle up then drop to 25ish% and if I go ahead and go 100% it just drops to 16%(idle)

I don't really think there is anything wrong with pedal or TAC for that matter. I've got a spare TB I think I'll swap it check the wiring and try again. Also log TP vs ETC pedel position.

 

If it's reading 100% at around half of the pedal travel, then you have the same problem I have. I never threw any throttle related codes either!

This is my theory:

The PCM is expecting a certain range of throttle movement from the Pedal/TAC. When you send the pedal to it's mechanical travel limit, it's sending signals that the computer sees as being out of range. At that point, it starts ignoring the pedal and just goes back to idle. Why it doesn't throw a code, I don't know. I suspect it's just because there is no "throttle control out of range" code for it to throw.

I have a picture somewhere that shows an electronic adjustable gas pedal next to a fixed gas pedal. In the picture you can see that there is about 1/2 the amount of total pedal travel in the electronic adjustable pedal than there is in the one that's fixed.

I still haven't figured out how to remove the electronic adjustable gas pedal from my Yukon to prove my theory, but in the end I don't plan on mounting one of those in my swap truck, so I'm not sure I care to continue exploring. I already lost one of the nuts that mounts the pedal to the firewall, and the mystery cable that moves the pedal in and out looks hard to replace and easy to break, so I quit trying.

So anyway, what I've done temporarily to fix the issue is to stack some magnets where the pedal arm meets the pedal base to limit the mechanical pedal travel to where throttle position hits 100% on the scanner. I have not had a single issue with reduced power mode or the engine just falling to idle and ignoring throttle input since I've done this mod.

Long term, I'm going to customize the pedal so it doesn't ride so high, and in general just make it fit my cab floor a little better.

 

Thanks! I'll try that. why wouldn't that have been a problem from the start instead of something that has developed?

 

"So anyway, what I've done temporarily to fix the issue is to stack some magnets where the pedal arm meets the pedal base to limit the mechanical pedal travel to where throttle position hits 100% on the scanner. I have not had a single issue with reduced power mode or the engine just falling to idle and ignoring throttle input since I've done this mod.

Long term, I'm going to customize the pedal so it doesn't ride so high, and in general just make it fit my cab floor a little better."

Jim, I found the same issues w/ the 05 H2 pedal in my 55....Idle to 100% doesn't come close to the pedal base.
I am going to follow your lead, and make an adj stop to allow for fine adjustment at 100%.
I data logged mine and never see more than 99.6%...

 

I wish I knew, but from your description, it may have been there all along, you just hadn't held it WFO for long enough for the computer to get pissed off and quit talking to the pedal/TAC.

 

Have you had any problems with the pedal not responding after keeping it mashed to the floor for more than 5-10 seconds?

I hope the day comes that someone unlocks this mystery <caleditor>

 

I will have to pull some OE scans and share them.

Hey Jim I was up in Wisconsin a few weeks back to tune a truck for a friend. I was thinking about stopping by to have a look at your issue, but you have a solution for now and I needed to get back to Rock Hill. Maybe one of these day I can head up.

 

Yeah, it's really not a big issue for me anymore, but figuring out why where and how to fix it properly would make me feel better if nothing else