Anyone done this. What is involved? What do you lose going from OBDII to OBDI ? I read that you must change the knock sensors.

first off, why? ODBII isn't that much of a hindrence towards power production.

As for your question... IIRC, the 95 and 96 harness is about as identical as they are gonna get. I would have to sit down with both helm manuals (or at the very least, Corvette Electronic Ignition and Fuel Injection: 1982-2001) to see what differences there are.

The other thing is the CCM...

Why? A lot of folks have done it. They must of had a reason.

Two good questions:

1: Why would you have to change the knock sensors?

2: Why oh why would you want to do this when there is Tuner Cat for OBD2 and you allready have a datalogger?

Seems like a really stupid change to make when the 96 PCM has alot better adjustment resolution.

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Thanks, that was a great help! Where did I say I wanted to do it?

The knock sensors in the '96 are 100k ohm while the '94-'95 style
are 3.9k ohm.

A little tact goes a long way!

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I might be wrong or my answer incomplete but didn't people do this to take advantage of low priced OBDI tuning software? I seem to recall reading that somewhere...

That's one big reason. Doesn't sound stupid to me!

That's one big reason. Doesn't sound stupid to me!

Change knock sensors and transfer your LT4 knock module over to the OBDI PCM. Then plug it in and away you go. You can even get a tune installed to the PCM before you plug it up so that you don't have to do it while at a shop where it can be tuned immediately.

As for why do you want to do this? It's cheaper to do the conversion and buy the software needed than it is to buy just the software and cable for the OBDII stuff. OBDII is not superior to OBDI with these cars. If anything it's more of a pain because of the added codes. You'll be fine staying with OBDII though. It used to be that ODBII software for the LT1/4 cars was crap(yes LT EDIT is pure crap) Tuner Cat was only available for the OBDI cars. So to make everyone's life easier, they switched to OBDI. Your choice now on if you want to do the conversion. Look around and investigate some more, especially prices. You may be able to find a deal on the OBDII stuff and save time and money by not converting.

I had a problem with my OBDII computer breaking up over 6,000 rpms. I was told by my tuner that it "couldn't keep up". Sure enough, the car was fine after throwing in an OBDI computer. It could be that I have a problem with my OBDII computer. However, I've heard of several more people having that same issue with the 96 computer. Plus with OBDI, you get no stupid codes every 10 minutes and TunerCat is cheap.

Oh yeah...first post on C4guru

Believe me I have looked. Not finding much for the OBDII LT1/4. It was only OBDII for two years so there is not much support. Why are they all so expensive?

Jonescap, good to see you here

Back to thread allready in progress

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Yeah, I wondered where all you guys went :wave:

Back on topic now, fer sure.

I like the OBD1 set-up better too.

OBD2 is more expensive to tune. You can do flash style OBD1 car for free if you look hard enough on the net.

Most on here mean well, don't take their comments the wrong way.

OBDII LT stuff is no more expensive the LS stuff which is also OBDII. Well, it wasn't at the time. Competition with the LS stuff has gotten so fierce that may have changed. OBDII is a huge change over OBDI.

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Our cars don't have LSX motors? I really don't see how LTX OBD2 stuff, being the same price or more than LSX stuff, relates to this at all?

To the OP, if you do the swap, you'll have a flashing SYS light just below the MPH indicator. As far as I know, there is no way to correct this. I've seen OBD1 PCM's from PCMforless that were supposed to be special OBD1/2 conversion computers still have this problem.

Just out of curiosity, why are you asking about the swap? Is it tuning related?

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Inquiring minds want to know. I try to learn something every day. I may never do it but want to make my own decision. You have already stated it.

"I like the OBD1 set-up better too.
OBD2 is more expensive to tune. You can do flash style OBD1 car for free if you look hard enough on the net."


What's your source for the flashing sys light, I have read everything I can get my hands on about this and that is a new one.

The two 96 corvettes I've seen with OBD1 PCM's have the issue. One of them had the converted PCMforless PCM, the other was with the stock ECM from a 1995.

I don't really know what causes the light to flash, my guess is that it's somehow related to the CCM, but that's a guess at best. I don't have a ton of experience with the OBD2 to OBD1 swap, just a couple cars. It seems like most people stick with what they have or go stand alone.

I just re-read my post, and I really came off like an A-hole. That wasn't my intention, lol.

No sweat Josh, I am just trying to learn! You are never too old.

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DropTop, you seem to have some sort of issue with me and i have no idea why mate, but i think you should get over it. Im not and have not given you a hard time, and im not about to. Seems youre taking the written word to mean something that isnt intended, and there is no future in that.

No good ever talking to me about tact, im not interested. You cant please all the people all the time, and im not about to change for anyone so i can.

I could sugar coat things for people until the cows come home, but at the end of the day, im not going to beat around the bush, i say it like it is seen to me, i ask direct questions, i give direct straight forward answers, and im quite sure most people have no problem understanding what i say.

If you take offence to people being honest and upfront with you, im really sorry mate, but im not about to lie. I know you like to learn something everyday, so maybe learn to stop taking everything i say so personally, then you and i will get along just fine. If you were to meet me in person (which in the comming months you may very well have the chance to do since ill be in your area) i think youll find im quite an easy bloke to get along with.
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My point exactly Josh, ive heard of people using 94-95 PCMs on a 96 before, and ive never found out a good reason as to why. From what ive seen on the CATS OBD2 tuner program i had a trial version of a while ago, the increments for change were substatially smaller, which to me, led me to believe the PCM from a 96 is indeed capable of more precise calculations. To top that off, i have also heard of people that have moved up to a 96 PCM for a 94-95 car, albeit a rare move, its been done, so given that along with the other info, it begs the question to me, why would you go backwards?

Ive heard of a few people having break up issues over 6,000rpm, TobiJohn was one of them if i recall correctly. I simply dont understand how this could be something that is excepted as normal for a 96 PCM.

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Good memory! Actually, mine was/is breaking up over 4500rpm or so. The dyno operator thought it might be an ignition problem. Still, it got to 290HP on a Mustang dyno which still isn't bad. I posted over there after the dyno run but there was no clearcut consensus on what might be causing it. Car has just over 50K so I thought I might replace the plugs/wires to see if that resolves it:

Case, I am sure you are a good bloke. You say you don't sugar coat things or care about tact. That approach sometimes rubs people the wrong way. Calling an idea stupid because you may not agree with it is perhaps not the best approach for a representative of this site.

I would be glad to talk about it over a pint anytime. The first round is on me!

Well youve read between the lines there mate, cause i didnt say it was stupid, i said it seems really stupid. That's not saying youre stupid or anyone else that does the change is.

The fact i may or may not rub people the wrong way isnt really something that is ever going to change no matter what anyone does, there will always be people that read too far into things, and others that dont like the way something has been expressed. If i was going to insult someone id be taking it to private message, so there is nothing written in open forum that i mean people to take offence to. They simply took it wrong if they do, and nothing i can do will help that. Im not saying i dont care about tact, but i am saying my idea of it is different to yours.

We will talk more about that pint when the time gets closer mate for sure, but right now im going to jump the gun and crack open a tallie