I am currently in the middel of my v-6 to v-8 conversion in my 1992 RS 3.1 v-6. A few months ago i bought a totalled 88 IROC with 56,000 miles on it really cheap so i decided to start this project. The motor out of the IROC, a 350 TPI is out and totally detailed, and now my 3.1 is out of my 92. Now im ready for the install, but during the whole process i have noticed a few things that are different, i knwo all about what has to be changed, and everything thats a neccesity, so im not asking those questions, there are plenty of posts everywhere for that, but im asking particularly about the dash, the speedo, and a couple minor differences i have noticed. First the dash in my 92 is totally different from the dash in the 88. Will my 92 dash still work, and if so what has to be changed, or does anything have to be changed ? I also noticed when taking out my computers of both cars that the 92 has 3 plugs going into it, and the 88 only had 2, i was curious what the extra third, yellow plus was, and if its gonna cause me issues, i get really panicky when it comes to wiring so please help me out, and i really dont wanna change my dash so any help there would be greatly appreciated also. I was told from a guy that in order for my speedo to work all that had to be done was to change the sensor in the tailshaft of the tranny, is this true, or is there more to it than that ? As for everything else i think i have it pretty much under control, i just really wanna get this dash thing straightened out so i can quit worrying so much about it. Thanx guys and i hope you can help me

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Nobody else gave this a shot, so I'll impart my ignorance and move it back to the top where somebody who does know what they're talking about will answer.

For your dash, the tach will need to be a V8 unit. The original could probably be modified, but I couldn't tell you what you'd need to change.

The story on the speedometer sounds right.

I don't know exactly what your two ECM harnesses look like, but as I remember it, my '86 carb ECM had three connectors on it. Perhaps you're not seeing the split correctly. At any rate, one goes to the left to the dash, the other two go to the kick panel to the engine compartment. Since you'll be using the '88 harness from the engine compartment to the ECM anyway (right?), just swap them out. The connector that isn't part of the engine harness should be the same on both.

Wait, the '92 has VATS, the '88 doesn't. Never mind, you're hosed. Change the whole dash, wiring harnesses, et al.

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I don't see how VATS will be an issue. You are using the 88 ecm and wiring right? You just won't have VATS anymore, that's all.

 

VATS is computer-dependant? I thought it was it's own separate module, buried in the dash, that affected the ignition switch?

Some tachometers from GM had a switch on them, to allow for 6cyl or 8cyl operation. Maybe you'll get lucky and find it on the back of the dash's circuit board.


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I read a write up of this swap, except it was a newer engine and ECM to an older car. The best way to get this up and running to gut the inside of your car and and put the older dash in. Or at least the gauge pod and other wiring. This will be time consuming, but at least you know that you'll have all the wiring straight and won't have to chase down a gremlin.

Chris

 

All the write ups I have seen out there suck, no one has a complete how to, and probably no one will ever have one because of the many differences between years and engines (its never the same that you are doing) Just so happens that I am doing the same swap. Except that I am putting an 89 TPI into my 92 RS. That 3rd plug 'has' wires for the IAC, Fuel pump signal, EGR solenoid #1 #2 #3, MAP Signal, MAT signal, TPS signal, Purge control, SES light..list goes on.
There is no reason to swap out dashes at all. YOu can still use the same tach even.
What you really need to do is get a copy of the wiring diagrams for the 92 and the 88 and compare between the two. This way you will know exactly what you are looking at and know what you need to do.
As for the VSS, your 92's VSS feeds directly into the ECM from the VSS on the side of the tranny (purple and yellow wires on the black 32 pin connector going to the ECM). The buffer for the 92 is a yellow box behind the dash on the passenger side up and to the left where the ECM is, this nmight be there to send a signal to the cruise. The 88 gets its signal from the back of the speedo then goes through a buffer (on back of tachometer) then sends the siganl to the ECM and cruise if equipped. The ECM between the two years reqiure different pulses from the VSS, I think the 88 ECM needs a 2000 p/mi and the 92 requires a 4000 p/mi. However this could be different from what I have explained, trying to remember right of the top of my head. Like I said, I think the best thing to do is get a wiring diagram for both cars and a pin location for both ECMs.
Couple of things to be aware of as well. It may not matter to you, but if you are going to use the AC you need to pay attention to the AC wiring, they are different between the cars, not just a slight difference. Also, are you using headers?...it might make a difference on clearence issues in the engine compartment where the heater lines run to the heater valve and radiator. The lines run along side the frame on the passenger side where as the lines on a V8 (not sure about all V8s) run on top of the frame. I could not get the the passenger side header (TES) on untill I replaced those lines with the V8 lines.
As for the VATS, I don't think you are hosed at all in this part. Like 'cdartz' said it should not be an issue. I am almost positive that there is no VATS in the 88 started in 89?. So there should be no problem at all, you can read more about the VATS here:

http://www.sethirdgen.org/vats.htm

Right now my swap is going fine. The last thing I need to do is solve a couple of wiring issues because the alternator is on the starter side compared to where on the 92 it was on the drivers side. I did not have an 89 wiring harness so I went with a painless wiring and that only took 2 hours to install, its nothing like most people are saying.

It's a simple swap, just very time consuming
HTH and Goodluck,
If you have any questions email me privately.

 

You can't use the same tach, if you take out your tach now, I bet it has 6 cyl printed on the back of it.

 

Doesn't the tach on a the V6 have three prongs
as where the V8 tach has four prongs?
Correct me if I'm wrong.

Because my 91RS has three prongs on the back
of the tach (it was a v6, now its a V8).