The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Doing LS Swap

**MidLifer** · 09-07-2020, 12:28 PM

I don’t know if member 68fouronthefloor is still doing this but when I did my lq4/4l80e a few years ago he sold me a pre-stripped oem harness and ecm with vats and cats removed (cats = you also have to deprogram the downstream o2 sensors, since you won’t be putting catalytic converters in). Price was very reasonable and I have had no issues with the gm harness other than it isn’t as pretty as the aftermarket ones. lt1swap.com has great instructions about the relays you’ll need and how to graft the harness into existing wiring. Sounds like your in-cab harness is pretty hacked up so you may want to just rip it all out and start over. American Autowire has good harnesses (not ls harness but what you’d need for the rest of the truck) at competitive prices.

Other lessons learned:

I tried to keep the in-cab tank and put a high pressure pump in it. Because I had a return-type fuel rail, the gas running back into the tank caused a smell and the pump sounded like a dentist’s drill. I ended up getting a Boyd’s welding tank in back.

If you are going to use -AN type fuel line (the braided type) buy the Teflon lined type. Ethanol fuel will vaporize right through rubber fuel line, make your cab and garage smell and eventually rot it out.

Note that after you get the truck running you’ll want to have the ecu tuned to increase hp and perhaps tighten the shift map for more fun. Find a local tuner, I’ve heard the mail order jobs are variable in quality. Should cost about$400 the first time (that includes the software license) and $200 fof subsequent tunes if you want to keep fiddling.

Also if you want a more classic gas pedal feel you might want to switch out your air intake to a drive-by-cable one. The earlier LS engines had them and you can find them everywhere. Then you can keep your stock gas pedal and even the cable iirc.

Feel free to dm as you go through your project. There are tons of little tips and tricks and I can’t remember them all here.

My swap was by far the best thing I did for my truck. No more low vacuum stalls, better gas mileage, and starts up in all weather with one turn of the key. Oh yeah, and runs great on ethanol regular gas. No more paying up for premium.

09-07-2020, 12:28 PM	#18
MidLifer Senior Member Join Date: Apr 2011 Location: South NJ Posts: 1,261	Re: Doing LS Swap - I have no idea what I'm doing! I don’t know if member 68fouronthefloor is still doing this but when I did my lq4/4l80e a few years ago he sold me a pre-stripped oem harness and ecm with vats and cats removed (cats = you also have to deprogram the downstream o2 sensors, since you won’t be putting catalytic converters in). Price was very reasonable and I have had no issues with the gm harness other than it isn’t as pretty as the aftermarket ones. lt1swap.com has great instructions about the relays you’ll need and how to graft the harness into existing wiring. Sounds like your in-cab harness is pretty hacked up so you may want to just rip it all out and start over. American Autowire has good harnesses (not ls harness but what you’d need for the rest of the truck) at competitive prices. Other lessons learned: I tried to keep the in-cab tank and put a high pressure pump in it. Because I had a return-type fuel rail, the gas running back into the tank caused a smell and the pump sounded like a dentist’s drill. I ended up getting a Boyd’s welding tank in back. If you are going to use -AN type fuel line (the braided type) buy the Teflon lined type. Ethanol fuel will vaporize right through rubber fuel line, make your cab and garage smell and eventually rot it out. Note that after you get the truck running you’ll want to have the ecu tuned to increase hp and perhaps tighten the shift map for more fun. Find a local tuner, I’ve heard the mail order jobs are variable in quality. Should cost about$400 the first time (that includes the software license) and $200 fof subsequent tunes if you want to keep fiddling. Also if you want a more classic gas pedal feel you might want to switch out your air intake to a drive-by-cable one. The earlier LS engines had them and you can find them everywhere. Then you can keep your stock gas pedal and even the cable iirc. Feel free to dm as you go through your project. There are tons of little tips and tricks and I can’t remember them all here. My swap was by far the best thing I did for my truck. No more low vacuum stalls, better gas mileage, and starts up in all weather with one turn of the key. Oh yeah, and runs great on ethanol regular gas. No more paying up for premium.