GS4-LT1

Hello All,
Is it possible to switch out the OBD1 to an OBD2 on a 94. The connection is already there and from what I understand 94 was the transition year. What all would need to be done if it is possible? Thanks as always.
-Mike

caddyboy84

Try getting a OBDII connector at the junkyard and use a diagram from one of the manuals and wire it in, it may plug right in for all we know. Doesn't hurt to try.

GS4-LT1

Isn't the 94 an OBD2 connection with an OBD1 computer?

caddyboy84

Thats a good question, which connector do you have? I have the Snap-on 2500 OBDII scanner and it reads both, the older 2500 don't. If your plug is OBD I, you might be able to swap the plug with some McGuyvering. I'm sure the amount of wires are the same, you'd just have to place them properly in the plug. I'm sure an OBDII scanner would read it, it's all money making BS by simply changing the plug you gotta buy a new scanner.

rodj

Just the ALDL or the whole system to OBD2 ?

GS4-LT1

The whole system

Cliff Harris

The OBD II communication protocol is completely different from the OBD I. The '94 computer doesn't speak OBD II and it wouldn't work.

Even the '96 (which does speak OBD II -- the first year that does) isn't fully OBD II compliant and it only responds to a limited set of OBD II commands. Full OBD II compliance didn't happen until 1997.

[EDIT: I was wrong on this. What I remembered wasn't true. See post #12]

caddyboy84

Thats a strange thing to want to do, what would be the benifit?

96GS#007

Interesting way to spend a lot of time and money for basically no benefit other than the added codes you'll need to program out.

93Rubie

Huh? Where did you get that nugget of info.
I'm fairly certain 96 and newer is OBDII compliant per federal law, PERIOD.

I agree with 96GS#007, why do you want OBDII system?
You have the ODBII connector with a flash-able OBDI PCM.
Any decent scan tool can communicate with that PCM using a standard OBDII cable. *Code readers are NOT scan tools.*

96GS#007

The difference between '96 and '97 & up are relative to the bi-directional controls. On a '97, you can change software parameters while the car is running and see what effect it has. On a '96, you cannot do this.

Cliff Harris

I was wrong about the timing of the OBD II communications in Corvettes. From Wikipedia's article on On Board Diagnostics, in the OBD-1.5 section (note the "subset" comment):

"...the 94-95 Corvettes have one post-catalyst oxygen sensor (although they have two catalytic converters), and have a subset of the OBD-II codes implemented. For a 1994 Corvette the implemented OBD-II codes are P0116-P0118, P0131-P0135, P0151-P0155, P0158, P0160-P0161, P0171-P0175, P0420, P1114-P1115, P1133, P1153 and P1158."

In rethinking this, I remembered that the OBD II in the '96 Corvettes is fully OBD II compliant but does not report all the extended GM trouble codes (which are not part of the OBD II standard). THAT didn't happen until 1997.

My connection to OBD II is that I was involved in a project to write an OBD II scan program for Macintosh OS X. It's Open Source and available on my web site:

http://www.misterpeachy.com/OSX/OSX.html

GS4-LT1

Basicly if it was easy enough I wanted to use the ability of the OBD2 system to specify individual cylinder missfire. Like I said...If it was easy enough

toptechx6

As others have pointed out 94 and 95 cars have some similarities to OBD II vehicles such as the communication connector and downstream O2 sensors, utilizing them however is problematic.
The feature you desire (misfire detection) requires a crankshaft position sensor first available on 96 Corvettes, the sensor also requires a new timing cover and other related parts to function including a wiring harness to get the information to the PCM.
One suggestion if you are tracking down a misfire is that your 94 does have sequential fuel injection, with the engine idling try unplugging each injector in turn, when you find one that does not make a difference it is likely the offending cylinder.
Understand this simply identifies the weak cylinder, you will still need to determine if the miss is caused by lack of fuel/spark or mechanical condition, but that would be necessary even on an OBDII vehicle.

93Rubie

That and even OBDII vehicles will sometimes not detect misfires. Depends on when they occur. I (on purpose) had a 5.7L Hemi running on 5 cylinders by killing spark, did this multiple times NO misfire codes. That particular Chrysler does not monitor for them at idle.

PLRX

Im with Jim. Thats a lot of money and I dont think there would be any HP gains.

pcolt94

Lots of good information said already. But just to answer the "question" in simplified and different terms.

All the boxes PCM, CCM, A/C controller and EBTCM (brake computer) are all on the OB1 system bus. It speaks in OBD1 language at a 160 baud rate. All the systems are on the same page so they can communicate with each other.

A system that is OBD2 has OBD2 language and protocol. You can't just change a PCM (to OBD2) and expect the rest of the car to work as you think it should. All the other boxes and systems are designed to work together on the faster OBD2 bus and communicate with each other.

Doesn't matter what kind of connector that is installed, the 94 system is OBD1 electronics. It just so happens that it has the OBD2 connector is on for the transition year. It does make things a bit strange but does not change anything. It's a whole different world of electronics between OBD1 and OBD2 .

Just to add as I have heard from tuners that OBD1 cars are easier to deal with.

This is why you can't convert due to the system bus and protocol.

DVNCI

For the time/money/effort you would be better off doing the EFI Connection kit

Benny42

That won't happen without a crank position sensor. Those came in '96

GS4-LT1

Awesome explanation, makes perfect sense. Thanks to all