First off, Hello thirdgen community! i have been a long time lurker dreaming of doing a lsx swap. However, I have the opportunity to buy a 1995 TA. Has LT1 and 4l60e. It is missing wiring harness and stock pcm. However the seller says he has an extra pcm.... all this for 500 bucks!!!

Now to my main question: computerized cars are not my forte. Does a pcm have to programmed to the the specific car its in? or to put it differently can any lt1 pcm be straight swapped and plugged in to replace another pcm? is it plug and play across the board? or does it have to be programed to the specific car?

Thanks in advance I have tried searching for my answer but I don't exactly know how to search for it and explain it clearly.

 

Welcome aboard thirdgen.org.

The engine itself doesn't care, but you can't just mix and match the rest. '93 in particular is an oddball year, as it didn't use the MAF, and had a 4L60 transmission ('94-up had 4L60E). '96-'97 were OBDII, which had different sensors than the earlier years.

So, as long as the PCM matches the rest of your harness/sensors, it'll work. '95 seems to be the fav among the LT1 faithful.

The engine/transmission don't really car what car they're in, though...

 

The 92 and 93 Lt1s used an ECM which had a removable e-prom,speed density (no mas air flow sensor) the oil pressure switch was mounted on the drivers side above the oil filter,the intake and fuel rail has no crossover,non vented opti,non heated O2 sensorsand the exhaust manifolds had a bulky tube on the rear with a check-in valve.
94 non-vented Opti,intake and fuel rails have crossover,the oil pressure switch may or may not be above the filter some early 94s had them in the same location as the 92/93 models.heated O2s,new style TPS and IAC connection (round),the IAC no longer is screwed into the housing it will be held in with 2 tors screws.
95 has all this as above for 94 however it now has a vented Opti.and the system is like OBD1.5 can be a pain to work with as far as code scanning since it comes with an OBD2 aldl connector but its really OBD1 (special )
96/97 is OBD2
You can identify this quickly because the timing cover has a sensor in the bottom which h is your CPS crank position sensor and vented Opti. This engine can be run with earlier computers you just will not have connection to the CPS.....
There are a few more little differences but not big.

 

Perfect! exactly what I needed to hear.

So i have spent the last 48 hours or so reading up on wiring harness conversions by pocket and others.

for clarification. is the reasoning behind the lt1 wiring to third gen merge solely for components in the dash? If i were to swap the 4th gen dash into my third gen would zero wiring harness modifications need to be made? or am I missing something?

 

Most of the wiring harness for the engine is for the engine components to the PCM. Coming from your drivers side firewall you're going to one by one cut most of these wires and merge them into the LT1 harness you acquire. Among these wires are your gauges, fuel pump, starter trigger wire, 2 orange 10awg wires for your fusebox main power. When I did my conversion I printed off wiring diagrams for my car and for my LT1. I one by one tagged the wires and figured out which ones get cut and spliced and which ones didn't need to be cut.
If you swap the dash you will just have more wires to figure out. The only way you'd come ahead would be if you used the 4thgen wiring harness for both the dash and the engine. However you don't have at least the engine side and I can't see how that would save you any significant pain.
If you're not used to PCM controlled engines (such as I was) I would suggest taking your time not to hack the harness in your car and just concentrate on one project at a time and forget about the 4th gen dash for now.
You need to answer a few questions before you jump into things though.
What car is the LT1 going into? The '84 in your tag?
Was it originally a fuel injected car?
If the answer to the above is no, then there are a few ways to do it but maybe the easiest is to use the gas tank and sending unit in your donor car. They say (never did it) all you need to do is cut the filler neck a little.
Try to get a PCM from a '94-'95 LT1. They are OBD1 and will be easier to deal with.
Get a harness from '95 to '97 LT1. There are 2 types of ignition coils and they have different plugs. should be ok with '95+ .. if not, it isn't the end of the world to fix.
I personally used '96LT1, '94 PCM, '96/'97 harness.
Make sure the harness is from an automatic as the 4L60E is electronic controlled. If going with a T56/T5 then either auto or man harness will work.
This is a good site for LT1 reference material.

http://shbox.com/1/4th_gen_tech1.html

Don't be shy of the swap for all the wires, it isn't that bad once you understand where they all go.

 

Sorry, to directly answer your question.. If you leave your 3rd gen dash, the gauges each have 1 wire that would wire into the LT1 harness. Since you say you don't have that harness now, it wouldn't be connected to your 4thgen dash harness and therefore you would still have to make splices. Good soldering skills/practice, heatshrink and 3m electrical tape and you won't have issues with the splices.