5.3 drive by wire mistery

[hemi43]

I usually post in the Blazer/Jimmy area, but figured I would ask here because of the larger audience.
I just finished a 2003 5.3 swap into a 70 Blazer about a month ago, and it runs perfect except for an odd problem. The throttle plate will hit wide open throttle (WOT) with only about 50% pedal travel, which makes for a touchy throttle response.
All parts used for the swap came from only one donor vehicle which was in perfect running condition, so mismatched parts is not the problem.
The only modifications done to the PCM is the VATS was removed. Everything else is stock.
Any help would be appreciated.
Dan

[5150.4.67]

Try: Swap in known good pedal. And double check wiring and pin placement.

[hemi43]

Originally Posted by 5150.4.67

Try: Swap in known good pedal. And double check wiring and pin placement.

As I said in my original post, nothing has changed from the working donor truck, and the wiring for the TAC and pedal has not been tampered with.
This is a known issue, but can't find a fix for it.

[KEL]

does this thing have a TPS ?
I think you can check the voltage and see if it is a problem.
Just a guess.

[88Ironduke]

If its DBW the TPS will be part of the throttle assembly and is not serviceable/replaceable without replacing the entire throttle body. TPS voltage would most likely not be an issue because the PCM will go in to low power mode if there is a disparity between TPS circuit legs and TAC module. It might be worth a trip to someone who is running HP tuners or equivalent and see just exactly what the PCM is reading and commanding. Otherwise you're troubleguessing and not troubleshooting.

just my .02 cents
Paul

[MrMeseeks]

Just a thought, but you may want to check if there is a relearn procedure for the tps. Some cars have that. Not sure what the doner car was though.

[hemi43]

Originally Posted by MrMeseeks

Just a thought, but you may want to check if there is a relearn procedure for the tps. Some cars have that. Not sure what the doner car was though.

We are using HP Tuners, and there's no relearn option for 03-07 because this setup uses a TAC module. Newer DBW can be retaught.
This is a problem that's been talked about on the net, but no one has had any luck finding an answer. I can learn to live with it, but it makes for a touchy pedal especially on rough roads.

[Willie Makeit]

I have the same issue, and this is with an LSA supercharger. Pedal way way too touchy. Searched high and low for an answer with no luck. Logged both the ETC (electronic throttle control) and the TPS (throttle position sensor) simultaneously in HP Tuners and found that this is exactly how it is even in the original setup. It is NOT linear in nature, meaning at 50% throttle pedal the throttle body is NOT at 50% or half open. What we discovered is GM did this intentionally in order to smooth out acceleration to mimic the drive by cable throttle bodies. Lots of guys on the Corvette forums talk about improving throttle response with the drive by wire throttle bodies for this very reason.

The problem is when the pedal is used in our trucks, the angle in which the foot depresses the pedal is DIFFERENT than the angle when it is in the 03-07 style vehicle. In the original setup, the foot tends to make the pedal use the fulcrum point on the pedal linkage more. In other words, we make the pedal "seesaw" at the attachment point more than we do when they are mounted in our year trucks. We tend to push straight with little to no "seesaw" motion.

I also learned that when power is turned off, the pedal re-calibrates to set itself to ZERO once power is reintroduced, so I used that to my advantage. Me and a friend fabricated a "stop" behind the pedal, reducing travel by approx 1/8" of an inch. The stop is not in the WOT (wide open throttle) position, but in the IDLE position, so when power is cut and reintroduced, the pedal tells the PCM to idle, but it is not as far back in it's "throw" as it would be if it went back to stock position. Less pedal travel to (smaller arc) in an effort to have pedal travel the same as the throttle body. I still have WOT. I still have idle. I just have less pedal travel between the two points. It did reduce the "touchiness" of the pedal slightly (or maybe i'm just imagining it since the pedal travels less <shrug>), but it's still not as "linear" as I'd like with regards to the steep (instant) torque curve increase due to the supercharger.

Not sure this helps, but wanted to share what I've learned.

[hemi43]

Thanks Willie;
This has been an ongoing problem for a number years by quite a few people. I would have hoped that by now someone would have found a fix. I also was going to machine a stop, but never thought of doing it at the return side of the fulcrum (idle). I will mess with it a bit to see if I can make it a bit more comfortable to drive. I can live with it, but it sucks trying to accelerate smoothly on rough roads.

[TooTall]

I'm pretty sure that in HPTuners there's a few tables that can be changed for the pedal position and relation to the TB opening. Pedal position vs throttle area or something

[Hart_Rod]

Originally Posted by TooTall

I'm pretty sure that in HPTuners there's a few tables that can be changed for the pedal position and relation to the TB opening. Pedal position vs throttle area or something

This is correct.

[hemi43]

Originally Posted by TooTall

I'm pretty sure that in HPTuners there's a few tables that can be changed for the pedal position and relation to the TB opening. Pedal position vs throttle area or something

Only for 07 and up pedals that don't have a TAC module.

[Hart_Rod]

Originally Posted by hemi43

Only for 07 and up pedals that don't have a TAC module.

The 07 and up have a TAC module, it's just built into the ECM. I will check my 06 tune when I get home, but I was pretty sure it would let you play with the pedal response somewhat. I'll take pictures of the tables if I find them.

[Willie Makeit]

Originally Posted by Hart_Rod

The 07 and up have a TAC module, it's just built into the ECM. I will check my 06 tune when I get home, but I was pretty sure it would let you play with the pedal response somewhat. I'll take pictures of the tables if I find them.

That would be awesome! Thanks rob!

i've read horror stories on guys poking around in the TB / ETC tables and bricking their ECMS.

[Hart_Rod]

Originally Posted by Willie Makeit

That would be awesome! Thanks rob!

i've read horror stories on guys poking around in the TB / ETC tables and bricking their ECMS.

I've seen that also. You definitely need to do some research before you start messing with the tables. I'll look this evening and see if I can find them for the earlier tunes.

[Hart_Rod]

Here's a picture of the table I found in my Gen3 tune that allows you to adjust the pedal response. Full disclosure: I've never tried adjusting this table and would do some research before messing with it.

EDIT: I found this thread on HPTuners that discusses the issue with Gen3 truck pedal response:

http://www.hptuners.com/forum/showth...pedal+response
http://www.hptuners.com/forum/showth...pedal+response

[Willie Makeit]

Thanks for sharing Rob, unfortunately they are discussing how how to make the throttle pedal more responsive in regards to pedal-to-throttle body movement, and we'd like to do the opposite.

This is where I've read where guys have bricked their PCM's by lowering these numbers in an effort to take throttle response OUT. Thus my hesitation to poke around in here very much.

[hemi43]

I sent an e-mail to the guy that runs LS1swaps.com , and he said all of his 5.3 conversions have this problem, and no one has found a way around this unless they use an 06 and up operating system in their PCM. I can live with it, so I'm not ready to start doing drastic changes like that for fear of making a paper weight from my PCM. I'll wait till someone figures out a fix, or if it really bothers me, I'll convert it to a drive by cable.

[Willie Makeit]

one does not simply run a Gen 4 OS on a Gen 3 PCM ... it doesn't work like that

[Hart_Rod]

Originally Posted by Willie Makeit

one does not simply run a Gen 4 OS on a Gen 3 PCM ... it doesn't work like that

True. My 2006 PCM is a Gen3, I think 07 or 08 is when they went to the Gen4s

[Willie Makeit]

my bad, was under the assumption Gen 4 started in '06

[Willie Makeit]

Rob: took your numbers and plugged them into a tune and then compared that tune to my existing tune. The graph was drastically steeper in relation to pedal travel vs TB travel in my tune versus the one with your numbers. Plugged your numbers into my tune and dayj1 & I went for a little test drive. Definitely improved the over-sensitivity, but would still like a bit less "instantaneous" torque application so I came back to the shop (nice cool HVAC running) and did another 2.5% reduction in the 0 to 80% range (90-100 is still 100%). Doing changes in small increments for fear of allowing the magic blue smoke to escape from the PCM.

Headed to a local cruise-in later and will report back once that test flight is complete.

Thanks for pointing me in the right direction!

[Willie Makeit]

Post flight debrief: the 2.5% reduction across the scale is dang near spot on.

Before changes - top pic. After changes - bottom pic.

Magic blue smoke still contained in PCM.