Go Back   Corvette Forum > C4 Corvettes, 1984 - 1996 > C4 Tech/Performance
Sign in using an external account
Register Forgot Password?
Register Search Today's Posts Mark Forums Read FAQ Vendor Directory
Search
C4 Tech/Performance
L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Welcome to Corvetteforum.com!
Welcome to Corvetteforum.com.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join Corvetteforum.com today!


Corvette Store
 
 
C7 Parts & Accessories
C6 Parts & Accessories
C5 Parts & Accessories
C4 Parts & Accessories
C3 Parts & Accessories
C2 Parts & Accessories
C1 Parts & Accessories
Wheels & Tires
Sponsored Ads
 
 
Vendor Directory
  
Reply
 
 
 
 
Thread Tools Search this Thread
Old 03-26-2012, 12:42 AM   #1
GS4-LT1
CF Senior Member
 
GS4-LT1's Avatar
 
Member Since: Jul 2007
Location: Eau Claire Wisconsin
Default OBD1 to OBD2 on a 94?

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
GS4-LT1 is offline   Reply With Quote
Old 03-26-2012, 12:57 AM   #2
caddyboy84
CF Senior Member
 
Member Since: Nov 2011
Default

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.
caddyboy84 is offline   Reply With Quote
Old 03-26-2012, 01:02 AM   #3
GS4-LT1
CF Senior Member
 
GS4-LT1's Avatar
 
Member Since: Jul 2007
Location: Eau Claire Wisconsin
Default

Isn't the 94 an OBD2 connection with an OBD1 computer?
GS4-LT1 is offline   Reply With Quote
Old 03-26-2012, 01:10 AM   #4
caddyboy84
CF Senior Member
 
Member Since: Nov 2011
Default

Quote:
Originally Posted by GS4-LT1 View Post
Isn't the 94 an OBD2 connection with an OBD1 computer?
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.

Last edited by caddyboy84; 03-26-2012 at 01:13 AM.
caddyboy84 is offline   Reply With Quote
Old 03-26-2012, 01:50 AM   #5
rodj
CF Senior Member
 
rodj's Avatar
 
Member Since: Aug 2000
Location: Sydney Australia
Default

Quote:
Originally Posted by GS4-LT1 View Post
Is it possible to switch out the OBD1 to an OBD2 on a 94. What all would need to be done if it is possible?
Just the ALDL or the whole system to OBD2 ?
rodj is offline   Reply With Quote
Old 03-26-2012, 03:58 AM   #6
GS4-LT1
CF Senior Member
 
GS4-LT1's Avatar
 
Member Since: Jul 2007
Location: Eau Claire Wisconsin
Default

The whole system
GS4-LT1 is offline   Reply With Quote
Old 03-26-2012, 04:52 AM   #7
Cliff Harris
CF Senior Member
 
Cliff Harris's Avatar
 
Member Since: Apr 2002
Location: Anaheim CA
Default

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]

Last edited by Cliff Harris; 03-31-2012 at 11:56 PM.
Cliff Harris is online now   Reply With Quote
Old 03-26-2012, 10:15 AM   #8
caddyboy84
CF Senior Member
 
Member Since: Nov 2011
Default

Quote:
Originally Posted by GS4-LT1 View Post
The whole system
Thats a strange thing to want to do, what would be the benifit?
caddyboy84 is offline   Reply With Quote
Old 03-26-2012, 02:31 PM   #9
96GS#007
Tech Contributor
 
96GS#007's Avatar
 
Member Since: Apr 2000
Location: Los Angeles CA
Default

Quote:
Originally Posted by GS4-LT1 View Post
The whole system
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.
__________________
Jim
'96 Grand Sport #007
A few mods here and there
96GS#007 is offline   Reply With Quote
Old 03-26-2012, 08:17 PM   #10
93Rubie
CF Senior Member
 
93Rubie's Avatar
 
Member Since: Sep 2010
Location: Indiana PA
Default

Quote:
Originally Posted by Cliff Harris View Post
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.
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.*
93Rubie is offline   Reply With Quote
Old 03-27-2012, 12:56 AM   #11
96GS#007
Tech Contributor
 
96GS#007's Avatar
 
Member Since: Apr 2000
Location: Los Angeles CA
Default

Quote:
Originally Posted by 93Rubie View Post
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.*
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.
__________________
Jim
'96 Grand Sport #007
A few mods here and there
96GS#007 is offline   Reply With Quote
Old 03-27-2012, 02:57 AM   #12
Cliff Harris
CF Senior Member
 
Cliff Harris's Avatar
 
Member Since: Apr 2002
Location: Anaheim CA
Default

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
Cliff Harris is online now   Reply With Quote
Old 03-27-2012, 03:23 AM   #13
GS4-LT1
CF Senior Member
 
GS4-LT1's Avatar
 
Member Since: Jul 2007
Location: Eau Claire Wisconsin
Default

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
GS4-LT1 is offline   Reply With Quote
Old 03-27-2012, 05:24 AM   #14
toptechx6
CF Senior Member
 
toptechx6's Avatar
 
Member Since: Jun 2006
Default

Quote:
Originally Posted by GS4-LT1 View Post
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
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.
toptechx6 is offline   Reply With Quote
Old 03-27-2012, 08:44 PM   #15
93Rubie
CF Senior Member
 
93Rubie's Avatar
 
Member Since: Sep 2010
Location: Indiana PA
Default

Quote:
Originally Posted by toptechx6 View Post
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.


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.
93Rubie is offline   Reply With Quote
Old 03-27-2012, 09:50 PM   #16
PLRX
Southern California
St. Jude Donor '09-'10-'11-'12-'13-'14
Support Corvetteforum!
 
PLRX's Avatar
 
Member Since: Aug 2005
Location: Riverside County
Default

Im with Jim. Thats a lot of money and I dont think there would be any HP gains.
PLRX is offline   Reply With Quote
Old 03-27-2012, 10:07 PM   #17
pcolt94
CF Senior Member
 
pcolt94's Avatar
 
Member Since: Jan 2006
Location: Orlando FL
Default

Quote:
Originally Posted by GS4-LT1 View Post
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
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.
pcolt94 is offline   Reply With Quote
Old 03-30-2012, 03:14 PM   #18
DVNCI
CF Senior Member
 
DVNCI's Avatar
 
Member Since: Jun 1999
Location: Bowling Green KY
Default

For the time/money/effort you would be better off doing the EFI Connection kit
DVNCI is offline   Reply With Quote
Old 03-30-2012, 06:54 PM   #19
Benny42
CF Senior Member
 
Benny42's Avatar
 
Member Since: Feb 2006
Location: Magnolia Tx
Default

Quote:
Originally Posted by GS4-LT1 View Post
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
That won't happen without a crank position sensor. Those came in '96
Benny42 is offline   Reply With Quote
Old 03-31-2012, 06:26 AM   #20
GS4-LT1
CF Senior Member
 
GS4-LT1's Avatar
 
Member Since: Jul 2007
Location: Eau Claire Wisconsin
Default

Quote:
Originally Posted by pcolt94 View Post
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.
Awesome explanation, makes perfect sense. Thanks to all
GS4-LT1 is offline   Reply With Quote
Old 03-31-2012, 06:26 AM
 
Go Back   Corvette Forum > C4 Corvettes, 1984 - 1996 > C4 Tech/Performance
Reload this Page OBD1 to OBD2 on a 94?
 
 
 
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Confused over OBD1 and OBD2 nwarner2010 C4 Scan & Tune 17 10-26-2013 02:25 AM
92 LT1 OBD1 change to OBD2 is recommendable? ruizsand1 C4 Scan & Tune 4 06-20-2013 05:20 AM
OBD1 vs OBD2 xphnmn C4 Tech/Performance 11 05-25-2011 10:04 PM
94 vette, OBD II codes pcolt94 C4 Scan & Tune 5 12-05-2007 09:33 PM
What do you use to diagnose OBD1 computers....... ghostmech C4 Tech/Performance 6 01-05-2002 03:59 PM


Tags
1997, 2500, 95, catalytic, chevy, communicate, compliant, converter, corvette, flashing, lt1, obd1, obd2, pcm, scan, tool


Thread Tools Search this Thread
Search this Thread:

Click for Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump


All times are GMT -4. The time now is 09:46 PM.


Emails & Password Backup