GMC93

I had this issue too and it took a few tweaks to the original tune to get it worked out. Possibly ask the tuner to take another look.

Steve L.

I picked up my truck from the second shop yesterday. They fleeced me for almost $400 without fixing anything. Drove the truck home with the O2s unplugged and it ran pretty well. I’m going to completely rewire the O2 harness and see if that helps. If not, I’ll have it tuned to run without the O2s in open loop all the time.

PS. Anyone in the Waterloo, Iowa area that wants to know the name of the second shop so they can avoid it feel free to send me a PM.

GMC93

not good... sorry to hear that

Greg Hansen

I'm so sorry to hear about all your problems. I had exactly the same thing and am still not totally fixed. My biggest problem was that after totally having to rebuild my engine after inspecting the innards I had to try and fix my problems as I could afford them.
The biggest difference I found was getting the plug gaps correct, making sure that I had good plug wires. I actually bought two new coil packs to replace the worst offenders. The other thing I found was to replace everything I could from the original L31 in my truck. I put in a really aggressive cam so it was really hard to figure out what was wrong but once I replaced the entire exhaust with 2.5" performance cats, muffler, tail pipes and new style 02 Sensors, the truck ran much better. After all that I sen my recorded log back to the tuner and magically all my codes finally went away.
Good luck.

Steve L.

What "new style" o2 sensors are you running? I've installed new AC Delco AFS105 sensors.

Greg Hansen

I ordered the ones that are from a 2004 LQ4 Silverado C2500 from Rock Auto Delphi Part # ES20008. These are the upstream 02's, I had the downstream ones removed from the tune and from the truck.

Greg Hansen

Hi again, I just looked up the 02 sensor that you used and it appears to be the one from your original truck. I had such trouble with the originals that I went to the ones used in the 2004 truck.
Any luck yet? By the way, I used Justin from Blackbear Performance for my tune. He's the one that seems to have cured my P0300 and misfire problems.

Steve L.

I want to update this thread with the solution that was finally found a couple of weeks ago. I broke down and to the truck to CJ Tunes in St. Paul, MN. Carl needed less than thirty minutes to diagnose and resolve the problem that had stumped me for three years.

The problem was with O2 sensors. I had installed and ran a 411 ECM in the truck for awhile prior to the LS swap. Carl said that bank 1 is on the passenger side of an L31 5.7L. The ECM was still reading the O2's as though bank one was on the passenger and bank two on the driver side. Carl reconfigured the banks to an LS orientation and it runs properly in closed loop now. I can't say enough good things about Carl. He was excellent to do business with.