Official NBS 4.3v6 to GEN 3 V8 swap Guide

finding a harness from a manual truck will be the easiest way, but you can use either. since you'll have the manual t-case, you don't have to worry about finding one with the electronic 4x4 wiring. also, if you use a harness from an auto, you can pull out the transmission wiring (with the exception of the VSS & reverse). click my sig to find the company i sent mine to (because i didn't feel like fiddling with it). it also shows the jumper you'll have to add to the fuse block for the clutch safety switch (which you can just reuse from your V6 harness).

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Originally Posted by zebra

finding a harness from a manual truck will be the easiest way, but you can use either. since you'll have the manual t-case, you don't have to worry about finding one with the electronic 4x4 wiring. also, if you use a harness from an auto, you can pull out the transmission wiring (with the exception of the VSS & reverse). click my sig to find the company i sent mine to (because i didn't feel like fiddling with it). it also shows the jumper you'll have to add to the fuse block for the clutch safety switch (which you can just reuse from your V6 harness).

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Thanks for the info. I read over your thread, and Current wiring is about 25 miles from me. Convenient. lolc

No. Mine is an auto harness. It already has all the manual stuff in it, just shut off. Plug it in, program the PCM with a manual trans file. Drive truck.

funny... my harness came from an 01 Tahoe & wouldn't start until i figured out the thing with the clutch safety jumper. no power to the starter - just like trying to start without pushing the clutch pedal in.

I already have an issue with the clutch safety switch(I think), sometimes it just wont crank. Turn the key again and its fine.

bypass and see what happens

If this info has been posted before I apologize, but I can't seem to find it. My truck is an 02', so I know I at least need a 99-02' harness, sensors and computer. But, how much newer can the actual engine be? In some places the 07-08' engines with low miles are cheaper than the high mileage older ones.

Right up to 2013 with a bit of work.

I've got a motor and accessories, but finding a flywheel has been a bit of a challenge.

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Originally Posted by blacstar

you need to get a 2004-up harness. the pinouts are different. if ur truck were to come with a V8, it would have been dbw.

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so is it possible to move the pins to make the 99-02 dbc harness to fit a 03 4.3 dbc fuse block?

Guys i need some help. I just did my swap based off of this thread, but im having motor mount/frame mount issues. I have a 2006 single cab silverado 4x4 with the 4.3 and a manual 5 speed. I bought a 2003 5.3 engine. The motor is in my truck, mated to the transmission and i have the bolts in the passenger side frame mount. But my drivers side is not lining up. I used the v8 frame mount on the passenger side, and had to use my v6 motor mount on the drivers side for 2 reasons. 1, the v8 mount i have is made to mount flat, and my frame has the tubes on an angle, and 2; my tubes are longer then the v8 frame mount on the drivers side. So couldnt mount it even if i wanted to. This is a picture of what i have on the drivers side with the passenger side bolted up:

Attachment 9243
Attachment 9244

you sure you got 1/2 ton 4x4 mounting plates & mounts? mine bolted right up.

I got the correct motor mounts. Not sure I have 4x4 frame mounts though. Are they different in a 4x4?

yeah, 2wd & 4wd frame mounts are different
can't find the part numbers off-hand, but if you ask the dealership for the frame mounts for a 4x4 1/2ton, they should be able to get you the part numbers. usually eGay, the classified section here, or parts yards are the best places to find them cheap

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Originally Posted by zebra

yeah, 2wd & 4wd frame mounts are different
can't find the part numbers off-hand, but if you ask the dealership for the frame mounts for a 4x4 1/2ton, they should be able to get you the part numbers. usually eGay, the classified section here, or parts yards are the best places to find them cheap

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Good deal, thanks for the info man. Ill see what i can find. Another question, the motor i bought was missing the evap solenoid (one right behind the throttle body). I went and bought a new one at autzone but im still missing the line or hose that connects to the top of it. Where does that go? i may have to just buy a hose and run it myself but i dont know where the other end of the hose/line goes. Also, for some unknown reason the return line for the fuel, is gone, along with the clip and bolt that holds both the main fuel line, and the return line down. Is that something i can get from a dealer?

the evap solenoid has a flex line that runs back to where the fuel lines are
http://www.ls1truck.com/upload/files...es%20after.JPG

should be able to find one from a junk yard a lot cheaper than a new one (so long as the yard didn't cut it)

as for the fuel lines, i can't remember if some of the late model trucks went to a returnless system or not

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Originally Posted by Selbyvince

Good deal, thanks for the info man. Ill see what i can find. Another question, the motor i bought was missing the evap solenoid (one right behind the throttle body). I went and bought a new one at autzone but im still missing the line or hose that connects to the top of it. Where does that go? i may have to just buy a hose and run it myself but i dont know where the other end of the hose/line goes. Also, for some unknown reason the return line for the fuel, is gone, along with the clip and bolt that holds both the main fuel line, and the return line down. Is that something i can get from a dealer?

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you have a returnless fuel truck. 1 supply line and 1 evap. unless you already have you need a returnless fuel rail. tell your tuner to eliminate emissions and change fuel reference accordingly.

alright im confused then. I have two hard lines coming up from the fuel pump. And i do have a return style fuel rail on this 5.3. Both of the hard lines on the truck are the same size as well.

How am i suppose to plumb this up? I have to get a returnless fuel rail to plumb up one of the hard lines, and the other hard line goes to the evap valve?

Also i already have my ecu from nelson. They tuned if for a 2006 5.3 according to the sticker they have on the back of it. I never said anything about if i was returnless or return style to them, does that say anything to you as far as how they tuned it? Or should i give them a call on monday and try and find out.

Thanks for all the help guys, id never get this figured out without your help. Also i ordered a new set of 4wd 1/2 ton motor mounts yesterday off of ebay.
Part number: Left side: 15113849
Part number: Right side: 15113847 Anyone know if that is the correct part numbers for what i need? there wasnt a picture so not sure what they look like, but according to gm that is the motor mounts for a 2003-2006 4x4 1/2 ton silverado with a 5.3.

Edit: I had them remove the egr/air injection as at that time i didnt know if i had it, but my headers had the port. Im not sure if they deleted the evap or not though in the tune as i didnt mention anything on that. BUT, i do live where we have to do emission testing. With no cats going back on, and lets say i hook up the evap valve like im suppose to (considering its not turned off in the tune). Will i still pass emissions? they dont really do a visual inspection, just hook up to your obd2 port and read. I know i will have at least one "not ready" status for the cats. This motor didnt have air injection, but its supposibly turned off in the tune (not sure if that will give a not ready status too even though i didnt have it).. Just trying to be prepared on if i will pass or not.

Ok, i have 2 sets of the return style fuel rails. And cant find not one set of the returnless rails. Does anyone have a set laying around??

just buy it. sell both sets of return style to recoup.

Just found a set on LS1TECH. So good to go for now, hopefully when i get home next week ill be able to finish this.

One more set of questions, for now. I just read through every page of this, as well as your build thread zebra. I have a 4x4 (manual not auto thank god) and as mentioned above i have a 5 speed truck. My harness is for an auto so i have all the trans connectors for a 60E. Motor is already in, wiring harness hooked up other then the trans harness obviously. I couldnt find where you said you had posted something about a jumper for the the clutch pedal. And also, what do i need to do about my trans. Am i going to have to pull my harness back out and send it to have the trans harness modified like you did? Or do i have any other options?

Also i read on one of the pages in here that someone had posted up the part number for the frame mounts on a 2wd v8 truck. His part number for the "right side" assuming passenger? matched the part number for the right side 4wd frame mount that i ordered. Is the mount the same on the passenger side between 2wd and 4wd. Or did i somehow screw up and order the wrong mount. The gm website said the part number was for a v8 4wd 1/2 ton. So if it is indeed the same, i already have that mount, and all i need is the drivers side mount.

Part numbers i gathered for a 1/2 ton 4wd; left: 15113849 // right: 15113847
Part numbers from this thread for 1/2 ton 2wd: left: 15113849 // right: 15113848

anybody look into this and give me some insight?

Also my truck also already has electric fans. The 5.3 engine and harness i bought did not. Is my electric fans still going to run? I know there is a seperate harness running up from the electric fans, but my v6 engine harness has one extra conector by the fuse box that plugged into another connector that comes out of the harness coming up from the elctric fans. My v8 harness didnt have this connector. And im wondering if that had anything to do with making my electric fans work.

Edit: Called current perfromance this morning about the haness deal. They said to convert my trans harness to my 5 speed, and change the o2 sensor connections to female from male so they will just plug right in, would be $450. That sound right? Also asked him about the electric fan issue, and he said he thinks that is something that needs to be wired in? So no real answer on that. Does anybody know something about these issues?

call nelson.

Got the truck on the road about 2 weeks ago now. Over 600 miles on it and it Runs great, only issues is the battery light is on and i have a lean code. Nothing i cant sort out.

Ended up having to use a v8 4x4 frame mount on the drivers side and a v8 2wd frame mount on the passenger side. Also wasnt able to get my electric fans to run like factory so just ran it through a relay where they just run when the truck is on. Also have some leftover parts if anyone needs anyhthing shoot me a pm.

glad to hear it's up & running for ya! :D
the battery light might be due to the alternator not sending a status code that the PCM is expecting. that was an issue with mine. Justin @ Blackbear is aware of the programming fix to get rid of it.

Thanks, do you think it has something to do with being an older model alternator and my truck being a newer model. My truck is an 06 and the alternater is off an 02 ?

don't know... i originally thought the opposite because mine's a 99 & the engine/alternator are 01

ah, well probably not then. Ok, well how am i suppose to get it tuned without having my truck down again. Id have to send my ecu back to get some more tuning done on it wouldnt i? i was told you cant get a programmer to upload email tunes threw because they programmed the truck with my vin number but with the v8 codes in it. So supposibly the programmer wouldnt recognize my vin or something. Is this true?

if you're talking like a Hypertech PoS, i don't know. i've had mine tuned by shipping the PCM out, i've had one sent to me with a core charge so i could keep driving & send my old one back, and i've also datalogged with a laptop & emailed the files to/from the tuner then downloaded to truck from laptop.

i've also heard of the AutoCal that's a handheld programmer your tuner can load your file onto & then you can swap between stock & a few stored tunes whenever you need.

there's a few ways to skin the cat depending on who tuned your truck & the methods they offer.

yeah ill have to look into it, nelson did my tuning.

what kind of MPG's are youll getting? Im getting right around 13 in town and on the highway. I did the daily driving tune with nelson, i have 3.73s, and only mods are the long tubes, o/r y pipe, and a gibson catback with and a k&n intake. I do have 33" mud tires on 18s, but i put this same setup on all my trucks and none of them got this bad of gas millage. And my last 3 trucks were crew cabs with the 5.3. Thinking if its going to be this bad im just going to have them put the performance tune in it and do the cam swap like i wanted to initially. The truck runs good, but doesnt feel like it has the power it should. Even a 2nd gear pull isnt all that impressive. Only code i have is a lean code. Im still using my v6 MAF sensor, and was told thats whats doing it.

Also, was your RPM gauge correct after the swap? Mine definantly is not. It reads 500-1000 higher then what i really have. What about cruise control? What kind of wiring do i have to do to get that to work again?

i typically get about 14 all in-town & about 16-17 if it's 75% highway @ 60-65mph. that's with 33s on 16s, 3.73s, LTs, ORY, airaid intake. that's on a mid-grade tune (maybe .5mpg less than the 91 tune i had before). also consider i'm at 3500-4000' & we regularly have crazy wind (30kt+). in TX running 93, i'd see around 18mpg hwy @ 75. in FL with my 31s, i'd seen as high as 20.

if anything, i'd get the A:F doped out first before making any other decisions... not that a cam wouldn't help anyway ;)
my tach reads right - it didn't the very first time, but that was because i did the math & figured out Jesse programmed 4.10s instead.
no cruise in my truck.

maybe some other guys could chime in with their results

hmmm, wonder why mine is so low then. Ill have to get my tuning checked for sure. Im in texas so 93 is everywhere, but with the prices of gas these days i went the cheap route to save a few bucks at the pump and did the 87 oct. tune. Not sure what the deal is with the rpm gauge then if yours reads right, maybe they messed up with my gears as well. Ill shoot erica an email about it tomorrow. Thanks for the replies, and yeah if anyone knows the fix for the cruise id like to hear it, i pulled some wiring diagrams up and printed them out, im sure i can do some work with the wiring and get it to work, just didnt know if there was an eaiser fix. Didnt realize how nice it was until it didnt work anymore lol.

If i move some wiring around and get it to work ill post it up here for others that may be seeing the same problem.

Ok maybe I missed it, but maybe someone can help.

I have an 03 silverado 1500 2wd 4.3 v6 with a cable throttle.
What motor options do I have?

Use any 6.0 and swap in an 02 and earlier harness and computer? and use a cable throttlebody?

Can the stock v6 automatic tranny be built up to handle the 6.0 or would it be better to swap the 6.0 and auto together?

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Originally Posted by BrockGrimes

Ok maybe I missed it, but maybe someone can help.

I have an 03 silverado 1500 2wd 4.3 v6 with a cable throttle.
What motor options do I have?

Use any 6.0 and swap in an 02 and earlier harness and computer? and use a cable throttlebody?

Can the stock v6 automatic tranny be built up to handle the 6.0 or would it be better to swap the 6.0 and auto together?

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You can use any 03-07 motor (4.8,5.3,6.0). You will have to convert over to dbw. (Very simple) You will use the wiring harness for the motor you buy, and you can get with a tuner and have them flash your computer to work with the motor.
IMO, the trans should be fine to start off with unless your doing something crazy with the motor.

So complete turn key 03-07 engine, and harness, and flash my v6 comp with my vin for the new engine.
What about the DBW and gas pedal? pull that from the doner as well, if possible?

Also read the 03 is a PITA, why was it an odd year/transition?

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Originally Posted by BrockGrimes

So complete turn key 03-07 engine, and harness, and flash my v6 comp with my vin for the new engine.
What about the DBW and gas pedal? pull that from the doner as well, if possible?

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Yes, they will have to alter your vin in the tune so that the computer knows it's a v8. But for the most part yes. Yeah you'll need the tac module which is mounted where your cruise control module is on your truck (if you have cruise). The wire going to the pedal, and the pedal itself. Nothing to changing all that out. Fun part is going to be finding the correct frame mounts. I went through 3 different sets before I found the ones that made my motor line up. And even then they were mix matched.

yeah, about the mounts - remember each side has 2 pieces (what bolts to the engine & what bolts to the frame). the plates that bolt to the frame are specific to light duty frames (1500) and heavy duty frames (2500 & 3500) as well as also being different for 2wd or 4wd.

I got my cruise working, oddly enough, I had my vin changed in the tune and it started working. Weird, but ill take it lol.

yeah, my tune's VIN matches the tahoe i pulled the engine from

Ok quick question, I have a 2001 v6 5 speed and a late 99 nbs 4.8 5speed
Can I simply remove everything including pcm from the 99 and drive it without tuning? Or is vats gonna get me with a no start?