I am very early into my ls1 swap and have a few questions.
What are you guys doing about the obdII connector? i still need to remove VATS and such and from my understanding must be done from the diagnostics port. I have a complete ls1 parts car (minus the t56) that i have stripped out completely. I recently removed just about every wire from the car, from the fuse block to the tail light wires, and now I am stuck with a giant rats nest and very confused. I am trying to weed out anything that has to do with the body control module, which is just about every wire inside the firewall. But i am stuck on the obdII connector. I read the ls1 miata swap featured on swaptastic and he states what each wire behind the obdII connector goes to, but there is way more to it. For example, he states the purple wire is the diagnostic wire, but when i followed it through the harness, it lead to a dead end that split into 4 different wires. Im pretty sure one of the goes to the cluster for the cel, but not completely sure which one after the split is the actual diagnostics wire. Is there a place to wire this into the engine wiring harness? (from my understanding the ls1 harness is standalone) I know which wires are supposed to get ground and power, just not the diagnostic wire itself.

Are you guys sending out your ecu's to be tuned? (like vats and rear o2's) If so where can I send it to that is reasonable?

Did you give up on your own harness and just buy one? How much? ease of installation?

I have been searching frantically lately and now im asking for some expert advise.

 

I'm no expert, but here's what I did for my LS3 swap. I assume the LS1 is not too different in this part of the wiring. I bought the crate engine, harness and computer from the local GM dealer. The only wiring I removed from the donor car was the engine management stuff and whatever else went to the Mazda computer. I had a rats nest too, but I unwrapped the original harness so I could trace out the wires and compare everything to the wiring diagrams (which I got from the Mazda dealer - I think it is available online somewhere as well). I removed *most* wiring that wasn't connected at both ends. The GM OBDII connector in the harness doesn't have a lot of wires in it and I put it in the slot below the fuse cover where the hood release was (I say 'was' because I had to remove all the hood release and latch for the cold air intake I put in). I left the Mazda OBDII connector where it was - mostly dead now! I also left the Mazda diagnostics connector in its original location even though most of the functionality is absent. The GM bulkhead connector has the CEL, VSS and so on there, not the OBDII connector.

 

Ha welcome to the nightmare!! It would be handy to know what year your car is, what your donor is and where you are at.

I'm no expert for sure but I spent 5 miserable years as an electrical systems specialist at a large Chevy dealer so I have messed with a few wires in my day. Key disclaimer for what I am about to say - my car is not running yet so I have no firsthand knowledge on if any of this works!

OK to start with I have a couple posts in my blog that might help you some. There is not a lot of technical detail here but a good place to start anyway.

Jim and Jenna build diary, Miata LS1 Conversion: Snuggling into a big pile of wire!

Jim and Jenna build diary, Miata LS1 Conversion: It's easy to be brave from a safe distance…

Jim and Jenna build diary, Miata LS1 Conversion: The tangled web I've weaved!

In a nutshell I started with pin out sheets on the 2 big GM ECM connectors and just followed every wire on them. Some were not touched because they went to the engine harness. Some went to their matching wires in the Mazda harness and some were tagged and abandoned.

I did the same thing with the Mazda computer but nearly all of them were abandoned. It is a bit scary how much you cut out!

To answer your questions Yes I had my computer tuned when it was still in the Camaro and there is lots of stuff they can fix. Mine was tuned by Frost. He is not cheap but he is good. Where are located? Any big city will have a number of tuning shops and I would try to stay local. Not only is it handy if you need something tweaked but a local shop will know your emissions laws and how to work with them. Just google auto computer tuning, dyno tune, speed shop etc with your city and see what you find.

Tuning should cost around $150 or so. What they keep or drop depends some on emissions laws and what you want but the speedo, vats, turning the cooling fans on 10 degrees lower, gas tank pressure stuff and rear 02s are all pretty safe to fix. Depending on your donor year you may want to tune out the EGR, AIR and update the timing curve a bit too.

Just so you know on the vats you can tune it out but I decided to keep mine and use the body computer to run it and to let it do it's thing. Not because I wanted the vats feature but because it was cheaper than haveing my computer tuned again and I have all the stuff so may as well use it.

I was just kidding about this being a nightmare. This is not rocket science and no I would not use a standalone harness. Yes it is easier but you already have everything you need so it is a waste of 500 to 1700 bucks depending on what you use. There is a few relays to ad or rewire but none of it is hard to do, it's just time consuming. The good news is when you turn the key you will know right away if you got it right and it’s not going to leave you on the side of the road or surprise you down the line if you miss something now.

You are on the right track by reading. LS1tech and a ton of stuff in their swap section. Also there is a guy at about the same stage you are at you might want to follow here:
My Mean Miata

Swaptastic and Flyin Miata is also a good source but remember some of those are older builds and everyone is different.

I'll try to put more detail in my blog for you as I button up the wiring in the next couple weeks. But you get no more help from us till you do a proper build thread so we can see what you are doing!

Good luck man!

 

yeah my build thread is a little over due..... didnt want to start too early because the only conversion parts i do have are the engine and wiring.

Its a 2000 firebird, and I actually found the pinouts. The sad thing is the diagram wont open on my phone, so i need to go somewhere and print them out. Im guessing thats where i need to start, and just suck it up and learn to read it.

The transplant car is a 95, which is pre-obdII. So it needed the port anyways.

Im located in Jacksonville Florida.

 

2000 is a great year - no EGR and the good intake.

IMO the best $17 you could ever spend on you build would be right here:

2000 Camaro Firebird Factory Service Manual Volume 3 | eBay

You better grab it before Shannon reads this!