Hey smart people,

I have a 5.3 from 01 Silverado. It's dbw, everything came out of a donor.. I reworked the harness myself.
Car runs well, it's about 2500 lbs with 4.10 gears so it's a bit of a handful. One issue I've noticed for awhile is a lack of power over 3000 rpm.

According to the pid for throttle it won't open past 32%. No codes related to etc, tac, TPS, or pedal.
I do get random misfire codes.

I've also been watching map, it never goes above 10psi, which tells me throttle is not opening.

Key on, engine off throttle will go to 100%. But on the highway I floor it, it kicks down to 3rd and throttle is limited.

Ideas?

Just off the top of my head, is it possible there might be a fuel restriction?? Filter, bad pump or regulator, pinched line, etc.

I did test pressure at idle and in park revving everything seemed correct.

Fuel demand is minimal revving with no load. Check fuel pressure at the rail when the throttle limitation occurs. It needs to be under load.

Shouldn't it throw a code if it's creating a limit because of starvation?

Maybe, or not. Check it out anyway.

Before I route a high pressure fuel line into my passenger seat, wouldn't this show up as a lean condition in the afr? How would the pcm know if I had low fuel pressure?
I suspect the pcm isn't commanding the throttle to open because of some software issue.

Meanwhile, it would do NO harm to do a pressure check under load. The computer doesn't tell you everything. Once you know the true pressure, THEN look for glitches. Handle the physical side first. If you securely attach the lines there should be no issue.

Put the gauge under the wiper arm, and drive it???

an option.
I don't have wipers.

I did some poking around.
I have my tablet displaying desired tp and actual tp.
And they are the same.. I suspected abuse management, but after putting that back to stock and seeing that the pcm thinks I'm asking for 32%. And giving me 32% I looked at the tac module and pedal assembly.

Pedal voltages check out ok key on engine off. And throttle will go to 100%

Key on Engine on is when it acts up.

I played with grounds and managed to kill all pedal function.

Redid them, and got it back, now 24% max pedal.

I think I have a voltage leak or ground fault, lousy plug somewhere or the tac module is f'd

I'd expect it to set some check-engine-light codes if there was something wrong with the DBW system. If you have no such codes, the DBW hardware is probably just fine.

Have a look at all of the DBW tables and torque limiting tables, and compare them to the tables in a stock ROM. The PCM software has a bunch of conditions that will cause it to limit torque, and limiting the max throttle opening is one of the ways that it limits torque (retarding timing is the other).

Post the tune file and a data log.

So I just took it out and got as close to 100% throttle as I dared ... Ls in 2500lb car with 4.10s is a lot.

So I reverted my tune file back to the original and only changed the minimum parameters, vats, egr, mph shift tables and speedo settings.

It solved the throttle issue. Now I'll be more careful when I delete btm etc. 1 or two parameters between flashes/tests.

I had done the file compare before, but starting from scratch was the ticket! Good advice.

I'm having this exact problem!

ive got a 2006 5.3 from an avalanche in a 1972 g20. the guy i bought the motor from slimmed the harness and flashed the pcm to 'get me started'. it's been running great but as it got cold it started doing weird things. some times it limits to 30%. if i drive it around a bit, turn it off, then on, it'll get to 38%. then 55% next round. every once in awhile it'll open all the way up. it's like im driving a different van every time.

got an obdxpro and downloaded the pcm w/ pcmhammer and of course the OS is an odd one. wanted to get in there and turn off torque management and fiddle around, but im pretty much locked out unless i buy hptuner or something. Thinking about having a local tuner flash another OS and hoepfully that is one I can access - looks like it's what fixed your issue.