5.3 No throttle

[Beerj]

Just finished my gen 3 5.3 swap in my yj using a PSI conversions harness. This engine is dbw. Starts and runs fine but after a couple of blips of the throttle, I lose all throttle response and the pedal is essentially dead. Throws a U0107 code which from my research is indicating a possible grounding issue with the TAC module. As far as I can tell, there isn't a dedicated grounding wire for the tac module so I'm guessing it's grounded through the ecu and uses the same ground that is located where the harness splits to either side of the engine. Am I missing something obvious here? Of course, I could just buy a new tac module but I'd rather not just throw money at it until something sticks. I should also mention, I can apply light throttle to hold rpm but as soon as I give it any remotely quick input, it quits working. Also, I've also seen that this can sometimes be an issue if the ECU, TAC and pedal aren't all from the same vehicle. In my case, the ECU came from PSI but the pedal, tac and engine are a matched set. If this is the case, how would I go about fixing that since I don't have the original ecu? Thanks in advance.

 

[whiskeymakin]

You got the body/frame/engine/harness all grounded together good? My only thoughts

 

[Beerj]

You got the body/frame/engine/harness all grounded together good? My only thoughts

Yessir, at least I believe so. Harness is grounded to the head, other head is grounded to body and negative battery cable.

My latest developments show the ecu is essentially an 03. The pedal is 03-05 but the tac is showing as an 06-07 so I'm thinking that's the odd man out at this point. I'm going to call PSI in the morning to see if they've got any bright ideas.

 

[Lil ugly]

I dont know about PSI harnass' but I know that Painless had alot of notes about making sure that the grounds for the harness were done correctly for my 6.0. I dont have DBW but still it speaks to how important grounding is to the new motors. That being said it sounds like your getting some wrong info back to the ECU from the pedal/throttle position sensor. Could easily be the different years or just a bad sensor.. Not much help really but I like typing long responses with out helping.

 

[Beerj]

I dont know about PSI harnass' but I know that Painless had alot of notes about making sure that the grounds for the harness were done correctly for my 6.0. I dont have DBW but still it speaks to how important grounding is to the new motors. That being said it sounds like your getting some wrong info back to the ECU from the pedal/throttle position sensor. Could easily be the different years or just a bad sensor.. Not much help really but I like typing long responses with out helping.

The effort is appreciated! Seriously though, when I built my buggy, I struggled for quite some time to get it to start. Pholmann kinda sarcastically asked if I connected the ground at the back of the block, which I hadn't. It was then that I learned the importance of grounds. He also explained that the ecu works almost entirely by applying grounds to circuits rather than 12v which was news to me. Again, grounds are important. Well damn, looks like I just typed a bunch too just to say I agree. Haha.

 

[Beerj]

Small update. So I talked to the harness builder and he asked if the brake switch wiring was connected, which it's not. He suggested at least grounding the yellow wire which would usually be connected to 12v when brakes applied. Now, instead of losing all pedal, it goes into limp mode and limited to 1300 rpm. Still throws the U0107 code. He also suggested that I use dielectric grease on all of the throttle/tac plugs which I did but no difference there. He says my components are all correct (metal pedal, metal tabs on tac and computer flashed as an 04) but I have my doubts. Seems like most people with my current symptoms end up swapping out the tac, pedal or both. Everyone else finds a common broken wire near the throttle body but that's only on the factory harness. The other thing that makes me wonder is if I search for an 04 Silverado tac module, it brings up both metal and plastic mounting tab versions. So tac seems to be the most plausible at this point.

 

[Lil ugly]

simple solution seems to be to invite a friend over with the correct year chevy and distract him with beer and porn mags while you "borrow" his pedal to see if it fixes the issue.

 

[Beerj]

simple solution seems to be to invite a friend over with the correct year chevy and distract him with beer and porn mags while you "borrow" his pedal to see if it fixes the issue.

Unfortunately, I think I need to convince someone to buy an 04 Silverado first. Then on to steps 2, 3 & 4

 

[Zjman]

I'm just talking out my ass here but would it be cheaper to take it to a tuner to diagnose and tune instead of throwing costly parts at it ?

 

[Beerj]

I'm just talking out my ass here but would it be cheaper to take it to a tuner to diagnose and tune instead of throwing costly parts at it ?

Unfortunately, I'm sure I could get a new pedal and tac for way less than a new tune that probably wouldn't make a difference anyway. I considered that early on but after reading damn near every thread on the internet regarding this issue, it's almost always mismatched components that a tune wouldn't resolve, especially when I can get another tac for $20. However, if that doesn't work, then tuner might be the last resort but if I'm doing that then I may as well go to dbc and never have to worry about it at all.

 

[Beerj]

Quick update. Picked up a pedal and tac module from an 03-05 tahoe. The only visible difference is the identification number on the tac starts with an "A" instead of a "K". Swapped just the tac to start and everything works perfectly now. Not going to bother with the pedal since I had to modify the other one to fit and it works.

 

[Lil ugly]

Quick update. Picked up a pedal and tac module from an 03-05 tahoe. The only visible difference is the identification number on the tac starts with an "A" instead of a "K". Swapped just the tac to start and everything works perfectly now. Not going to bother with the pedal since I had to modify the other one to fit and it works.

That is good news. It is really frustrating that manufacturers change stuff in such minor ways without a clear way to tell the difference. had a similar issue with an oil pan on a 6.0 a little bit ago. Good that you were able to fix it though.

 

[Beerj]

Yessir. I fully expected it not to work. Especially since there's at least a couple of other versions besides the A and K. Got lucky on that one I believe.