Taken from a PM, but thought it should be on the forum for others to find useful information...
Quote:
Originally Posted by 69lsvert
Thanks for all the info. I decided to go with Holley on all my stuff, mounts, adapters,crossmember,headers, oil pan.
Now another question. All this is new to me so bear with me. The computer and harness what do I need to do with it. The guy at Holley said he had a comp and harness for 1750 and I passed.
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You already have a computer (PCM) and a harness?
Do you want to tackle modifying the harness yourself?
If the answer to the previous 2 questions is "yes", then you have some decisions to make.
First, I'm not exactly an "expert" on this stuff. However; I just completed my build so it's fresh in my mind and I've learned about some stuff I'd do differently the next time.
So, think of all the stuff you want to eliminate. Most likely that will be rear o2 sensors, EVAP system, skip shift (CAGS). It's also mandatory to have VATS (Vehicle Anti Theft System) deleted or your engine will only run for a few seconds and shut off.
Second, think of what you'd like the PCM to control (Besides the engine). If you plan on using the PCM to control your fans for instance. What about the reverse lockout? Will you install cruise control? Do you want the PCM to control your AC system if you have it (Recommended for idle control).
After you've decided on that stuff, you will need to send off your PCM to a reputable person that can reprogram it for you (unless you want to buy $1K worth of software and learn it yourself). Work with this person and get everything fleshed out that you want. When he/she is finished they should be able to provide you with a pinout and a wiring diagram. I was able to get someone to do mine for under $300 which included a base tune for my modifications (CAI, 3" exhaust and LT headers). I would also recommend buying a second computer. I was able to get mine from a junk yard on car-part.com for about $25. This way you can have one in your car and send the other one back for tuning and you won't be dead in the water. Also, after all is said and done, you'll have a backup.
When you have the pinout, you can start modifying the harness. The first thing is to remove all of the loom and then to remove all the wires you won't need. After that, (and I learned this the hard way) wait until you install your engine and other components. At that time, decide where you want to put the PCM and lengthen or shorten wires as desired. You'll also either need to use the fuse and relay box from the donor car or buy one. I got this one from Current Performance:
http://www.currentperformance.com/Ac...ies/SA-1k.html
Basically, the above kit is the crossover from PCM and engine to your car. It's the piece that makes your harness "stand alone".
Doing this isn't exactly "easy" but it's not really as difficult as you first think. I was scared my first time doing this but now I wouldn't hesitate to do it again as opposed to spending $1k on buying it premade.
Of course, there is always the option to buy a harness from PSI, Current performance, Speartech or what-have-you. Even GM has their own kits you can buy now.
The bonus about working with a tuner is that they can set it up almost exactly how you want it. My PCM has partial code from a Savana Van, Corvette, CTS-V and GTO. All working to give the control I wanted. For instance, a GTO doesn't have fan control through the PCM, it uses the BCM (body control module) so the code that controls my fans is from the van. My AC fan control is actually from a GM prototype vehicle. I wouldn't have known the first place to start without my tuner.
You could just control the fans with a thermostat and the AC with whatever kit your using but it's way nicer to have the PCM take care of all of that and it makes a lot more sense from the engines perspective as it should idle up for AC for instance, and it already has a coolant temperature sensor, so why not use that for the fans? I like it as integrated as possible.
Anyway, it's a lot to think about. The planning is key. You really need to decide exactly how you want to do it.
For a perspective on whether you want to do it yourself or purchase something. I spent about $400 total on my PCM programming and harness modifications. I also put in about 20 hours of my time.
Hope this helps!