What injectors are you running? I would run the injectors that the tune is for. You should see if you can get a computer for the 6.0, or get a 6.0 tune.

 

I am running an lq4 6.0 pcm and harness and everything. I'm also running the whole 6.0 injectors and intake and all sensors on the 5.3.

 

I still think it is the tune. The computer is thinking it is firing a 6.0, but it is only firing a 5.3. That is basically another cylinder worth of engine. Just think a 6.0 is .75 of a litre, and a 5.3 is .6625 of a litre per cylinder. From everything I have read, the first few seconds of starting does not work off of long term fuel trims (LTFT'S) like once it gets running. I would get a tune or get a different computer. Does the computer think there is still a 4l80e tranny in it (I'm not sure maybe there is one in there).

 

It has a 4l65e in it. We tried a 5.3 DBC PCM and it wouldn't even start with it. If I could find an 02 yukon XL PCM which those came with 5.3's we could rule out a PCM problem.

 

Have you checked the sensors on the side of the TB?

 

We used HPtuners to confirm that the TPS is reading right. And it would go from 0-100%. Also everything is plugged in.

 

Are the throttle blades physically opening to WOT while this is happening.

Have you checked each and every ground on it.

The tune is not going to cause the problem a 6.0 tune on a 5.3 will idle and run perfectly albeit a tad rich. Done it before more than once until I could get them tuned.

First thing you need is a live scanner to check it out without it you are pissing in the wind and changing parts wont fix it. You need hard data to make a diagnosis and get it back on the road.

 

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Something else just popped in my head. It says you swapped it in to an 02. Was the engine a newer engine? Some of the older engines had the fuel regulator on the engine, and the newer engines have the regulator in the tank. If there was no regulator in the fuel system, the pressure would be high letting the injectors flow more. Just a thought. Did you check your fuel pressure?

 

If there was no regulator, there would be no pressure, you would be pumping fuel through an open pipe.