jamesx17x

I have a 2003 Chevrolet Silverado with a 4.3 v6 under the hood. Just today I purchased a 5.3 v8 with 111k miles out of a 2004 Chevy avalanche. To have a successful swap what would I need to do so?
i have read the very detailed writing about the v6 to a gen3 v8 but that’s for a 4.3 going to 6.0. So I am still curious about some things. We did receive the PCM/computer and the motor mounts off the guy we bought it from. Any advice or help is greatly appreciated

RB04Av

Wiring for the 5.3 is IDENTICAL IN EVERY WAY to that for the 6.0; so all of that writeup stuff is equally applicable.

Since you have the ECM & harness that came on the V8, you should be good to go. There may be acoupla minor details to work through; the TAC for instance (I'm not the least bit acquainted with the 6-cyls, so don't hold me to any kind of standard of accuracy or completeness; but other than that, you're largely in business. The 6.0 swap writeups will cover all of that.

jamesx17x

Ok so since I have the ECM would I still have to get my current PCM reflashed/retuned into v8?
I’m assuming still go through acquiring the new fuel lines, ac hoses, heater hoses, radiator hoses, v8 torque converter, flex plate, fan shroud/e fans, the TB bypass for the radiator, air intake.

This one part of the write up confuses me a little

“you will also need a nipple that connects to the back of the intake manifold that provides vacuum for your brake booster, the 6.0 engines power breaks use their power steering pump. you can get this from the dealer or off a 4.8,5.3 intake manifold”

i would not need what is mentioned above because I have a 5.3 motor and intake manifold or am I wrong?

thanks for your time

strutaeng

That quote is assuming the 6.0 came from like a 2500 with hydro boost brakes. In your case it came from an Avalanche, which I'm pretty sure has vacuum assist brakes just like your truck, so no issues.

Yes, you'll need your V6 ECU reflashed for the 5.3. I believe the V6 stayed drive by cable for the entire GMT800 generation. Does the 5.3 you got have drive by wire? You got the harness too, right? You'll also need the TAC model and the gas pedal assembly to convert it to drive by wire.

Does the 5.3 has return fuel lines on the intake? Or is it the single fuel line (return less?)

jamesx17x

No the v6 is not drive by the cable I heard after 03+ they all became electric and going by that logic the avalanche being an 04 i would assume it’d have electric. I’m a novice when it’s comes to this but it seems the intake has return fuel lines on it due to the smell motor was taken out just today and running 2 days ago. I Can provide pictures if necessary

strutaeng

Double check your 4.3 truck on the throttle body. Yes, they all went to electric throttle body, but that's only on the V8s.

I do believe the 4.3 eventually got drive by wire but that's on the GMT900s.

jamesx17x

I did not get the harness due to the fact some wires were burned that’s why they sold it, I do plan on getting a stand alone harness. I did a little research and you are right how would I proceed?

RB04Av

The 03 Avalanche, same as my 04, had HB. (not sure all the V*s do but I kinda think so, starting in whatever year, it's a year thing not a 5.3 vs 6.0 or 1500 vs 2500 thing, butt in any case there's no 6-cyl Avalanches) Also is drive by wire. Also the 6.0 Escalade motor (LQ9) I have is DBW and it also originally came with HB. As far as I can tell, IDENTICAL IN EVERY DETAIL. Same same same same.

Since you have the V8 ECM you don't have to worry about reflashing the 6-cyl one. All that talk is moot.

Well duh. You have to have stuff that fits. If it won't bolt up then you have to get stuff that will. Lots of that stuff may or may not have come with your new motor; butt it's too dark out now for me to see if it's there though, and besides, your monitor is at the wrong angle. Regardless, if it didn't come with your new package, there's like BILLIONS of em in junkyards. Pickups have mostly all the same stuff, you don't "have to" find an Avalanche for the most part.

I'd STRONGLY recommend swapping over to HB. It's SO FAR superior to vac assist for brakes, it's like ... no comparison. Especially if all that stuff (apart from the HB itself) came with your new 5.3. Otherwise, go hit yer local buzzard nest, and pry em off of whatever you don't have yet, rather than dinking with vacuum fittings. You'll be glad you did. Mostly you need the HB itself, the hoses if you can get em, and the fluid cooler.

Should be the returnless system, just like the 6.0 would have had. Same same same same. Whatever the 6.0 writeups say to do, if they cover the 03 model year, will apply to your 03 5.3.

The 03 motor came with a clutch fan. You could certainly use that setup. However the later electric fan system is a dead drop-in. See the tech articles on this site for details. It's quite easy, almost effortless, to make the upgrade. Which I did to my 04 Av, and HIGHLY recommend. Major improvement in every way. I think you'd need the V8 radiator for that though, not sure that the 6-cyl one is the right size for it, I think they are 2 different widths, which you'd want the V8 rad anyway, no matter which kind of fan you use. Also not sure that the V8 fan shroud will fit on the 6-cyl rad. You don't need the shroud with the electric fans anyway.

DO NOT do that!!! WWWWWWWAAAAAAAAAYYYYYYYYY too much trouble, no good reason, and very high probability of unpleasant surprises. Go get one off a junkyard truck.

I suggest you go to a junkyard and spend some time LOOKING AT trucks before posting any more. We're not going to be able to give you an absolute step-by-step and complete parts list since we can't know what all you actually got with your new motor. Do some research on your own so you can ask intelligent questions instead of floundering in ignorance.