As you can see from my number of post, I am new to this forum, I have been doing some reading but not posting much, however I have a question that prob. has been answered many times in the past, but here it goes one more time.

I want to do an LT1 swap in my 91 Z, I am not new to the LT1's as I've been working with this motors for the past 8 years, I have done many LT1 swaps, but never on a third gen, well my 91 Z has the L98 I think, 350 TPI, I have located the computer and also have located the C100 connecor, my question here is.

Can the stock computer be removed from the car at all? is the C100 connector just for the instrument cluster? can I run an aftermarket stand alone wiring harness? sorry for all this questions.

I have read the stickies up top, but I can't find anyone that have used a wiring harness from painless or speartech, and that is what I would like to use, please help.


Jose

 

I used a speartech harness.. simply spliced in where it was labeled and removed all my old wiring harness that was for engine management and the ecm..

my car was carbed however.. the gauges I replaced with all autometer but the basic conveniences were left alone and still run off the stock fuse box..

just recently with my rebuild I ran a painless circuit boss to clean up the wiring some along with separate fan relays..

 

So this means that the stock ECM on a 91 can be removed, correct?

that way I can run a stand alone system, then reconect all the wires from the C100 for my gauges, am I in the right path here, or am I totaly lost.

Jose

 

Yep the ecm is removed and a pcm of your choice is put in its place with the associated wiring harness.. stock, speartech, painless, msd, etc...

My vote is for speartech but I am biased since I use it..

As for converting the gauges.. try texasLT1 on the board here, he has more experience with me on that since all my gauges were replaced.

 

The stock gauges with the exception of the speedometer do all go through the C100, the speedometer signal is in the C230 under the dash near the ecu, each of the harnesses i've built for th swap used the stock gauge cluster on 90-92 cars. The pulse is the same for the speedometer, the only time it gets a little tricky is when you want cruise since the cruise module uses an 8000 pulse/mi signal where the spedometer uses a 4000 pulse / mile.

 

'91 Z won't be a problem with the speedo, matter of fact you don't have to get a custom harness from speartech or painless if you have an f-body harness and that $500 can go to something else.

 

Easier than I thought it would be, thanks for chiming in fellas.. was tougher converting from carbed.

 

Man, this is great information, thanks a lot.


Klortho, as a matter of fact, I do have an F body harness, I have read the LT1 swap sticky, but I'm not so sure how it works, let me see if I am understanding what you are trying to say here.

If I have an F body harness from a 94+ car, I can use it in my 91? what about the trans, I don't plan on changing the transmission, I have a new 700R4 with a good stall converter already, and I don't want to spend any more money if I don't have to, you know what I mean.

so how can I make it work, can you please elaborate for me.


Jose

 

The stall you have should be able to work with a 4L60E, to make the swap as simple as possible, get one of those and swap the 700 out. This way the LT1 PCM is doing everything for the gauges, speedo tach etc etc and you won't have to purchase the TCI lockout kit (about 90 bucks) so the torque converter will lock out, you don't have to screw around with finding a '93 throttlebody for the TV cable going the 4L60E route either since the PCM does all the shifting in the tranny. There are about 8 wires that have to be spliced into the '91 dash harness to get the motor fired up and all gauges working, I myself think that paying $500 to get 8 wires to hook into my harness was a little steep.

 

Yes, technically you can get it up and running by hooking up a few wires, however someone doing a harness for $500 is typically doing a lot more than just connecting a few wires together, trust me i've done a few, getting it to run and getting a nice fitting harness and everything working properly requires a good bit more than just splicing 8 wires together.

 

But why spend 500 bucks on something that can be done by yourself and make it look just as good, people taking advantage of engine swappers imho, you can hook 8 wires up and make it look just as factory as anything else in the car, I can unhook the LT1 harness and plug it up into a '95 t/a or camaro and fire it right up, or put an L98 back into the '87 and hook it all up, no ends cut or soldered together and everything is under the dash.

 

To do that would require having an extra harness to cut up, the TPI harness just doesnt have connections that undo as you make it sound, the LT1 harness wont reasonably reach under the dash to connect up at the C230, and nobody is taking advantage IMO except for maybe speartech for what i've seen for a full harness from them, I know i dont charge $500 to wire it up, but theres a lot more to it than you are telling.

 

I guess if you think there is, I personally didn't run into a bunch of trouble wiring mine up, alot of the time was just tracing wires out but each dash harness is different anyway from V6 to '87 TPI, 88-89 TPI 90+tpi, then differences in camaro and firebird as well. But the plugs on my LT1 harness that have all the gauges in it were more than long enough to go through the passenger side of the car.

 

Z28*****,

You mean you can make an engine harness to work in my 91 without me cutting and tracing any wires? for $500.00 I will take one, The motor going in this car has cost me more than $8000.00 so buying a harness for $500.00 is not going to brake my bank, please let me know on this.


Jose

 

Let me ask you guys something.

Talking about gauges now, Do the gauges get their feed through the C100 connector on the firewall?????

Or is there another connector under the dash that I need to tap into???

from hat I've been reading in the last minutes, this is what I can come up with.

The stock 91 ECM is located under the dash pass side.

The ECM has 3 connector that connect to the ECM and go through the firewall to control the motor, am I right?

so to make my stock 91 gauges I need to keep supplying signal through the C100, am I correct?

Which in other words means that the stock TPI harness and the C100 harness communicate some how, right?

So if I want to swap my engine, I have to remove the engine and the stock harness, and there will be some wires to I need to cut and the splice to the new LT1 harness for the gauges to keep working, if in fact this is all it take, then it's not that hard to make.


Z28*****, if you can make the harness that I need I will still buy it from you.


Some one correct me please.



Jose

 

Jose, I can do whatever you want with the wiring, yes almost all of the gauge feeds themselves go through the C100 connector, the only one that doesnt is the speedometer pulse, it goes through the C230, the area where Klortho is leaving things out is he's making it seem you can just use a 4th gen LT1 harness and nothing else, sell off the L98, L03, etc harness or set it aside for converting right back, which isnt possible, the LT1 harness doesnt have the starter wiring, the power feed wiring, the wiring for relays for the fuel pump, fan 1 and 2 (also if someone is doing a swap from a tbi or V6 car, or non perf pkg 305 tpi car they have no 2nd fan relay or wiring), yes you may be able to drill a hole in the firewall and get the 4th gen connectors near the C230, or even take some of the wire and extend them into there, but without a thirdgen harness to cut up your going to be short the wiring for the power feed, the relays etc, yes i've done the same, made a harness that plugs into a 90-92 at the C100 and C230, plugged directly into the 4th gen LT1 harness, and didnt cut up any harnesses, it started with a brand new C100 connector and terminals, but most people dont have that at their disposal...

Klortho, what im saying is your leading people to think the LT1 harness will just hook right up with 8 wires, everything will work and they dont need a thirdgen engine bay harness, which simply isnt the case, you need a harness to start with, or someone doing the work who can build you a new one, the people that have someone do a swap harness, or at least those that have had me do a harness usually still have their harness to sell with the original injection setup getting them back most of the cost of paying to have the swap harness, so they pay a small bit more than someone doing the wiring themself but end up with a nicer product in the end.

Jose, if you want i can set you up with anything from your stock harnesses blended together to a completely new harness with you sending me nothing at all, PM me if you want.

 

PM you.



Jose