Help! Motor In--Dead, No communication

[Red03SilSS]

could it be the VAT's?

[TimeLimitHit]

could it be the VAT's?

probably not, you kept the same pcm initially and it would not start, correct? The computer has no idea what engine is in there, it will just try to run it based on its current programming. once you get your power issue sorted out you will need a tune. The 6.0 programming will run a 5.3, but not the best. The VE, fuel tables, spark timing, all that is going to be out of whack because of the smaller cylinder volume in the 5.3. The pcm will not auto-correct. It will "expect" a certain amount of air and thus inject a proportianate amount of fuel but it will actually be taking in less air and adding the same amount of fuel. The MAF will not correct it untill higher rpms as the engine does not use the maf for fuel calculations at low rpms, if it even helps. Being that the truck sees limited use, you can probably just drive it the way it is, but you might as well through a v6 in there if you arent going to tune it.

[Wtfan18]

sounds like a ground to me to, when i did my 98 5.3 obs swap the ground to the relay was not connected so the key would turn the gauges would work but i would get no starter when turning the key. DOUBLE AND TRIPLE CHECK the grounds...

[lechez71]

did you ever disconnect the pcm? i had a similar problem, it was the connectors.