I got me a Tahoe!

[Fless]

A few things I'd suggest:

1. Check the fuel pressure at the rail.
2. I assume that you have a scanner that reads individual cylinder misfires -- is #4 the only one showing anything significant?
3. Just to rule it out, do a quick CASE relearn. If the crank position sensor has been changed this might make a difference, and it's quick and easy.
4. What is the MAF reading in g/sec at hot idle? It should be close to the engine displacement in liters.
5. Look at the short- and long-term fuel trims. You could have an injector that's over- or under-fueling. Might do an injector balance test.

 

[Nutro]

I don't have a scanner but I just added one to my Amazon cart, a cheaper one ($250) because I just flat out need one.

I swapped injector to a good GM Flex fuel injector. I deleted the CEL code P0304 and let it idle for a bit. No CEL came back... yet.

If I rev it up in park, the idle hangs BAD, like if I take it to 3K RPM and let off throttle, it will take a good 3-4 seconds to come back down and when it does, it stumbles a little and starts smoking out of the tailpipe. Its not an oil or coolant smoke though, it smells like a lot of water in exhaust pipe and there is a ton of water/vapor/moisture coming out of the tailpipe.

 

[Fless]

I'll add throttle body cleaning to my list of suggestions.

 

[Nutro]

Not sure why half the muffler has mud on it and the other half is clean. Hmmm

 

[OR VietVet]

I'm watching the Army - Navy game..... Was distracted....

I am watching it too. Go Navy and looking good.

I thought he had said that in post #1 and was not sure, so I had to go look.

 

[OR VietVet]

I'll add throttle body cleaning to my list of suggestions.

If in fact #4 is the only cylinder effected, I have to lean at a vacuum leak, since the compression is right on spec at 170 psi.

 

[Nutro]

Well, ate some dinner then swapped out the throttle body for a new one I had on my fathers C10 LS swap. No real change. While idling, I disconnected each coil plug electrical connector and the idle changed on all except #4 so there is something going on there. I decided to drive it around the neighborhood and she's smoking pretty good now and might be burning oil.

 

[mikez71]

Keep an eye on coolant level.
Might check coil harness and make sure you are getting power and ground to #4 coil.

How did the sparkplug look that you replaced?

 

[Nutro]

Keep an eye on coolant level.
Might check coil harness and make sure you are getting power and ground to #4 coil.

How did the sparkplug look that you replaced?

It looked pretty good but was fuel soaked and had some wet oil on threads

 

[mikez71]

Definately check coil harness.
I think there have been a couple threads before that ended up being a bad harness.. can't find them now of course.

Some have problems from bad sparkplugs, new!

Another one was a bad injector.. perhaps you have a leaky one, that might explain the smoke too..