Can I use the same harness/computer from one LSx with another engine?
 

Okay, a bit of a story here. Got the LS swap running. Love it, does everything I'd hoped. Only problem is that there's a bad knock in our used engine. That sucks, of course. Trying to work it out with the vendor, but so far no dice, they're being difficult. More on this later after we resolve it one way or another. In any case, we're way too far into this truck to stop now, which leads me to...

My question of the day: If I were to just say screw it and purchase a new/remanufactured long block, is it as simple as buying a 5.3 LS-based engine and swapping it out? We have a custom harness, we have a computer dialed for the harness, we have all the accessory drives, manifolds, etc. from the current engine. The current engine is nothing fancy, no performance tune or anything, out of a 2002 Silverado. I'm not savvy enough to know if there's something specific about a given long block that makes it different from any other 5.3. I see here that Summit has a 5.3 GM long block, and that they specify it's for '99 GM trucks with a VIN beginning with LM7, but I have no idea why it's so specific, especially since it isn't as if they have an entire lineup of years/VIN prefixes to select from. Anyone care to educate me on this? Thanks!

Re: Can I use the same harness/computer from one LSx with another engine?
 

Yes, the long blocks are going to be essentially the same from '99-'07 (Gen III). You can't use an '07-up Gen IV engine with your harness/PCM.

LM7 is the RPO code for the "garden variety" common Gen III 5.3. It's the most common "LS" engine there is.

Re: Can I use the same harness/computer from one LSx with another engine?
 

Awesome, thanks. That makes sense! So a swap from our current engine to another should truly be "plug and play", no additional tuning or anything needed... perfect.

Re: Can I use the same harness/computer from one LSx with another engine?
 

I have heard some comments on the "O" ring being defective on the oil pump pick up and causing some problems like you describe, just saying!

Re: Can I use the same harness/computer from one LSx with another engine?
 

We have good oil pressure, so I assumed no oil circulation problems. Took the valve covers off, all looks good, operates normally. Could be a rod bearing, don't want to rebuild an engine that was supposed to be good - my pro mechanic friend thinks it could be timing chain problems. In any case I'm more than a little frustrated that this "Ready To Run" engine is crap. It drives, though, and I love it, so the motivation is still there to finish the job.

BR3W, I saw you posted, but I guess then you deleted your post. If it was important, let me know!

Re: Can I use the same harness/computer from one LSx with another engine?
 

I believe the fuel injector connections are different for trucks and cars. as is the maf.

Re: Can I use the same harness/computer from one LSx with another engine?
 

also if you replace the oil pump use the fat o-ring no matter what or you can have pressure problems

Re: Can I use the same harness/computer from one LSx with another engine?
 

This would not apply for him since he is looking to swap out long blocks if he goes that direction. He will swap intakes, injectors, sensors, accessories, etc to the new long block.

Re: Can I use the same harness/computer from one LSx with another engine?
 

Just an update... after three days of driving and consistent noise under all conditions, took it two miles to the tire shop the other day. Pull up in the lot, put it in park, about to shut it down - and the noise disappears. Shut it off. Start again - no noise. Have driven it around until good and hot - no noise. Cold start - no noise. Appears to be gone! Guess maybe the engine sat a while and had some gunk built up - my mechanic friend says maybe one of the lifters wasn't able to operate properly, but after a few days of driving and oil circulation whatever was in there broke down and got flushed out. Holy moly I'm stoked. Not gonna have to break the piggy bank after all... knock on wood.

Re: Can I use the same harness/computer from one LSx with another engine?
 

3 mo later, any updates?
Do you have a part number for the "fat" o ring for the oil pump?