I swapped the trashed 6.0 out of my buddy's 05 2500HD. The new motor had 130,000+ miles on it, but he needed a motor bad. I checked everything I could think of as far as connections. Crank sensor, cam sensor, grounds, starter, MAP, MAF, Throttlebody, Oil sender, O2 sensors, injectors, and coil packs. Everything is connected good except maybe the injectors...those were hard as crap to remove and re-install...not sure if I did them correctly.
The truck just cranks and kinda sounds like it's either backfiring in the exhaust pipe or gurgling water in the muffler. We did get it to start one time, but shut it off right away because of a loud tapping sound. After that it wouldn't start again. Shortly after that, we didn't have enough battery to try it anymore.
What should I check? I know the O2 sensors are blackened pretty bad and may have been water contaminated(owner drove through water and motor injested a lot of water and threw a couple rods out the block). The owner continued to drive the truck and start the motor. What should I be checking next?

 

Double check injector pack connectors. When I did my swap, one wasn't connected tight enough and it made the engine knock/tap really bad too. Scared me cause I thought something was wrong w/ the motor at first.

 

I got it going. My helpers didn't hook up the big ground to the engine block and I didn't bother to look over their work until today. After that everything went smooth. Thanks.

 

Well, I thought it was fixed and done, but I guess I messed up somewhere. It keeps going into reduced power mode. Do we need an obdII scanner in order to see the codes? I can't figure out what I did wrong.

 

Yes codes would be a good start. Write them all down double check your install for the specific codes and clear them. Then see which ones come back.

 

We had someone scan it and clear the codes. Took it for a drive and when it warmed up, it went into reduced engine power mode again. The guy cleared the code while driving and the truck went back to driving normal for a bit. We repeated this about 4 times. It kept saying lost communication with throttle position sensor or actuator or something like that. I'm assuming the plug on the side of the throttlebody may be damaged or a one of it's wires. Where is the TAC? The scanner mentioned that too.

 

What you doing with the 6.0 that was removed? Are you at a dealer, buy the core for the $300

 

The TAC Module is located on the cowl, on the driver’s side, to the right of the master cylinder when looking from the front of the truck and directly behind the fuse box. While it is possible for the TAC Module to fail, it is also highly unlikely. The most common issues and especially since the problem has reared it’s ugly head after a swap, is either a grounding issue or issues and or the actual harness going to the throttle body has a damaged wire. The wires are very small gauge and can be broken easily, as they can become brittle with age and heat. GM does sale a replacement pig-tail, but while it can become necessary, it also can present issues if not properly installed due to resistance. I know it’s aggravating, but keep your head up and I’m sure you will find the cause of the issue.

 

if you swapped the motor...wouldn't the PCM need a crank relearn?

 

No, I'm not at a dealer. The 6.0L I removed has two big holes in the block. I'm not sure if they can be repaired, but everything on the inside of the block is junk. One piston disappeared completley as well as 3 or 4 rods broken in half. I was hoping the block was in good condtion, but as soon as I took off the starter, the pieces started falling out.
There was a ground at the back of the block that got torn during removal. I used a butt-connector(I think that's what they're called...little sleeve type thing) to connect the wires back together. I've been told that may have been the problem. I suggested a crank relearn, but I wasn't sure if that would help the current issue. The kid did drive it 22 miles yesterday to drop it off with a real mechanic. He said the truck drove fine with no problems, but we'll see what's up when the real mechanic reports back.