Motor problems!!
 

I recently purchased a 2008 Sierra Denali with the 6.2 and after I bought I took it and had a tune put on it. The guy that tuned used hp tuners and said it would take a couple hundred miles or it to re-learn the changes. After driving it a while I wanted to see what kind of changes the tune made and matted it from 15 mph or so . When it shifted there was a pause or delay before it jumped into the next gear. I called the guy that tuned it about it and he said it was trying to learn the new shift point and to just drive normal for another hundred miles or so. Well after 100 more miles I tied giving it a 0-60 and the same thing happenend it ran good until it tried to shift them paused then shifted to the next gear . After I would finally shift it sounded a little different. Then on that same run at about 65 mph the check engine light start flashing as well as service traction controll. When I come to a stop i noticed a slight knock on the motor. Took it and had it scanned and the code come back cylinder 7 misfire . Can any one help me and tell me what might have to be done to fix this ??

Check your spark plugs and wires. Especially check the porcelain on the spark plug for cracks or chips. That's the easiest thing to check when a misfire code pops up. It may just be a coincidence that it happened right after your tune.

Lonnie

Would that cause the motor to be knocking ?

I don't think a single cylinder misfire code is tune related. Lonnie is spot on, check the plug compared to others. Be sure the wires and connectors are on tight, not a bad idea to use dielectric grease.

Do you have a shift kit or tuned shift points? Sounds like he is leaving trans control to PCM learning. That's a great idea with BMW SMG but not so good with GM PCM.

Yes, it could sound like knock. It shouldn't sound like rod knock but bad spark can do a lot. If ceramic or plug tip broke off it will likely cause internal damage. Try to isolate the knock source with stethoscope or knock ears. Bottom end, top end, in the cylinder, or what.

I had the guy take the tune off because I was scared it was going to mess it up more because of the way it was shifting but it's defenitly a top end knock. It's not real loud but noticeable and the truck still drives but not quite as much power . The knocking doesn't get louder when I'm cruising down the road though.

I check the plugs and everything think is good . The sound is coming from inside the cylinder.

Take the valve cover off and check out your valve springs and make sure nothing is broke.

Lonnie

Could it be the push rod since I was running hard when it happend?

Could be bent pushrod or other valve train. Pop valve covers and take a look before it gets worse.

So am I in the clear as far as having a rod knocking and having to replace the whole motor ?

Nothing is ruled out until you do some investigating. We're just giving you the easiest stuff to check. A rod knock is a pretty distinctive thumping sound. Most valvetrain problems are a ticking sound. You just have to tear into it and start inspecting.

Lonnie

It takes a LOT of damage to need replacing the whole motor. I never jump the gun to say replace motor unless you ran without oil.

What's your redline before rev limiter kicks in? How high did you rev the motor? Stock cam, valves, retainers, pushrods, etc?