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I put a new motor into my 2005 chevy avalanche. Bought HPTuners and downloaded the stock tune before I started. The motor is a 5.3 with 4.8 flat top pistons and a Brian tooley stage II truck cam. Pretty mild, just wanted a little bump in performance. I figured along with a tune it would pep it up enough. My problem, after the swap the computer is acting wierd. It won't crank at all, and when i turn off the key, after about 5 to 10 seconds, the dash lights come back on and stay on? Tried to connect HPTuners and also a handheld scanner but says "no connection". Can't understand what might possibly wrong. I didn't do anything accept disconnect the neg battery, unplug all the sensors, disconnect the starter, then exact opposite to reinstall!!!! Didn't mess with wiring or computer in any way. I'm new to this computer controlled stuff, can anyone point me in the right direction and give me an idea where to start.
Grounds are all cleaned and connected. Didn't do anything to the wiring, just disconnected and then reconnected everything. And the whole top end is all the stock components and sensors. Basically, just a short block upgrade. I have checked the DTC plug and I have ground at pin 4 and 12v at pin 16. Thing that was a little strange that might be a clue is that Pin 5, which should also be ground, was showing 2.4 ohms, and pin 7 which is the data link I believe, and should have like 3.5 v was showing 8 or 9 volts? I tried the security reset procedure, but when the dash lights come back on after turning off the key, that kindof ruins that, but the passlock light on the dash wasn't on anyway. Anyone got any clues? I have ordered a new BCM as I think that may be the issue. Checked fuses and relays and can't find anything wrong there either?
I didn't disconnect the PCM. Like i said, i didn't do anything except disconnect all the sensors, the ground straps and the starter. Then just reconnected everything when the new motor was in. I have checked and rechecked every connection. I put in a different BCM and it did the same thing. I have checked all the pins in the DLC and they all check out okay. I only have 4 pins, #2, #4,#5 and #16. 4 & 5 show good ground and 16 shows 12 volts. Not sure what pin #2 is but it showed about 7 or 8 volts. I worked on it all weekend checking everything I could check, cleaning connections, etc. Can't figure this out!!! Is there any way to check if the PCM is good? Somehow, I feel as if it connected to the climate control system. When I turn on the key, it appears everything is working okay. The radio comes on, the windows work, the power seat works. But when the climate control is activated, everything freezes. If i push the off button and keep the climate control from activating, everything will stay working, except it still won't crank. If I try to crack it, everything freezes. The only way to unfreeze it is to disconnect the battery, then reconnect and start over. Does the climate control automatically activate normally. I don't remember if it did before?
Just throwing this out there but maybe you crushed a wire putting the motor in. Sounds like you have a short somewhere. When you turn the key to on not starting does your check engine light come on and stay on? Does the Hptuner's box light when connected?
Actually, i did crush a wire. The ground wire that goes to the back of the block got crushed between the block and tranny bellhousing, but I loosened the tranny and fished out the wire, and then spliced a new wire on it and grounded it to the back of the block. So that should not be a problem. Otherwise, I have looked at all the wiring harness many time over now and cannot find any thing unusual. I tied all the wiring back and away from the engine when I dropped it in to make sure no wires got caught. Except for that ground wire, there was NO problems with the wiring. The HPTuners does light up, but after a while it just says something like "no connection made" or something to that affect.
The ground you crushed goes to the back of the cylinder head correct? Not the block, ive heard of weird crap happening with those grounds loose or grounded to the wrong spot. Also there is atleast 1 ground on each cyl head, prob more.
Modules dont generally just take a **** for no reason. The hvac module iirc is on a different network than the pcm so it shouldnt affect it.
There has to be a bad connection some where. I would first check the battery and its connections, a weak battery will make things weird. Check the back of both heads for grounds and any inline connectors. This isnt likely to be a sensor not connected, more like 1 that connects the engine harness to the body or something the like
I put the ground wire back on the block, not the head. Not sure where it came off of now. I was pretty sure it was the block. It should be okay to run them to both locations, shouldn't it? I will try that, splice in wires and go to both heads and the block.
Haven't checked voltage at the starter yet. Trying to figure out why the dash lights come back on and everything freezes first. I know I have a good battery. Made sure to keep the charger on it most of the time to keep it well charged. Have checked it and it shows 12.8 volts most of the time. Do you think no grounds to the heads could be the problem? Why would that cause these issues? There is nothing on the heads that should need a ground. But, like I said, I will splice the ground wire going to the back of the block and ground the heads too, see if that does anything.
No grounds to the heads shouldn't' be a problem. The truck grounds go to 2 spots on the block by the cam sensor and one on the block by the exhaust manifold near cylinder 1 and the power steering pump.
Yes, that is what i have. Actually, the ground that goes to the back of the block, the one that I got caught between the block and the bellhousing is two grounds that go into one connector. And then there are two grounds that go to the ground down on the side of the block by cylinder #1 behind the power steering pump. That is the way I have it connected. I have searched thoroughly for anything i may have missed, but can't find any thing. I was thinking, is there a ground to the frame somewhere?
Don't worry about insulting me, i'm human and make mistakes. If i am being a SF let me know, i can take it. I just want this fixed!!! I took every connection back of and cleaned them thoroughly, both the connectors and the connection location. Used a wire brush and sand paper and made sure they were nice and clean and shiny. Even the bolts that go into the block. Then put electrolytic grease on them and made sure they were tightly connected. Even took the starter back off, cleaned the connections and the surfaces where the started meets the block, cause the started is grounded by those surfaces, right?
I found some wiring diagrams on another site. The diagrams show a ground #103 that looks like it goes to the back of the pass side head.
I don't think I connected that ground. I have looked and don't see a loose wire anywhere in that area. What is this gound?
May not be the right next step, but I would go right back to the starter and see if you have 12v when turning the key to RUN. If you don't have a helper, drop the starter down. Put a jumper cable on the housing and the other end to the battery ground bolt. Take a small alligator clip and your voltmeter and attach to the small trigger wire on the starter. Place your voltmeter on the windshield so you can see and hit it!
Also do you have 12v on the heavy battery lead coming down to actually run the starter once its engaged? Be careful here...disconnect the positive battery cable at the battery before removing the starter! You don't want to take a chance of shorting the battery directly to ground while you're wiggling the starter down.
Also be aware that if it does engage and run, its going to jump around quickly. Secure it somehow.
I will try that, but I really think this computer issue is preventing voltage getting to the starter. There is absolutely no activity when trying to start it. Not so much as a clicking noise. Just absolutely dead. The only sound I hear is a slight clicking noise coming from down under the dash on the passenger side. Like a relay or something under the dash. But i will check the voltage. Did you say check it in the on position or in the start position? I did take it out and bench tested it and it worked. But have not checked voltage to the starter when it is installed.
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New motor, now computer problems??? 
