sinister-one

I just purchase a 99 Silverado. It had a 4.8 that was shot so I replaced it with a 5.3.


Question is.... do I need to swap the computer to the 5.3 as well ?

FFDP

iTrader: (2)

No, you can just tune the 4.8 computer to run the 5.3.

Or if the computer is very similar in year, like 99-02 you can just swap it right in. Either way would work.

sinister-one

The new 5.3 is out of an 02.
And the reason I ask this is that the motor has developed a little bit of a miss. I figured plugs and wires. Swapped them out yesterday and it ran really well. Went out this morning, it ran the same and then all of a sudden it's got the miss again.
So I was thinking maybe its the computer.

FFDP

iTrader: (2)

Without it in front of me I can say why it's misfiring but regardless you do not want to run the 5.3 at full tilt on a 4.8 tune. I wouldn't anyway, there are just too many parameters in the computer that are different between the engine programming that wouldn't make it safe.

I would say check for vacuum leaks and watch fuel trims and that stuff or even other readings from the computer to help diag the problem but even all those things are going to be skewed because the engine size is larger than what the computer is programmed for.

sinister-one

Any particular procedures in swapping out PCM ??

Wolftrk99

iTrader: (5)

Honestly probably be best to have it tuned, you have to have the pcm reflashed and when you do it will probably put the same os and parameters into the pcm, so you would essentially be back at square one!!!

2xLS1

iTrader: (25)

What injectors did you use? A 99 4.8 had 21.8 lb injectors and a 02 5.3 had 25.2 lb injectors.

sinister-one

using the 02 5.3 injectors. the motor was a complete swap out. Took out the 4.8 and replaced with a complete 5.3.

sinister-one

So tuning it JUST to get the right 5.3 parameter is still like a custom tune, correct ?


cost for a tune around here (performance tune) is $500 bucks !

2xLS1

iTrader: (25)

I would use the 02 PCM and put your VIN# in it and other things that may be different like rear gear ratio, tire size, fuel tank size...etc. If you ever want to add e-fans in the future you will need the 02 OS And no reason to spend $500 to get something like that done. Any competent mail order tuner with a bench harness could do what I suggested for way less. Shouldn't pay more than $100 plus shipping for that.