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“Pre-OBD” Diagnostics

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    Topic
  • #508607
    Patrick O'ConnorPatrick O’Connor
    Participant

      Hi everyone,

      I drive a 1991 Camaro with the 3.1L V6. It has the old ALDL diagnostic connector. I know that I can jump across two certain terminals to get trouble codes (12 = no distributor reference pulse, 13 = oxygen sensor, etc), but is this system capable of giving more information than that? More modern systems can give things like stored codes, long term fuel trim and other fancy stuff like that, does a system as old as mine have that capability if connected to a “proper” scanning tool?

      Thanks,
      PatrickO

    Viewing 9 replies - 1 through 9 (of 9 total)
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    • #508609
      davedave
      Participant

        Prior to 1995, OBD1 was a proprietary design; each manufacturer could come up with their own codes for whatever they wanted. Since 1996, OBD2 has generally been standardized among all automotive manufacturers.

        So, in short, who knows what you got or what information you get. Pulling OBD1 codes can be quite a mysterious procedure.

        #508641
        John B KobberstadJohn B Kobberstad
        Participant

          A Snap On MT2500 has the capability. There are 3 different adapters for GM vehicles. One is for GM ABS and my guess would be the other 2 are for engine and body computer connection I’ve never had the opportunity to use mine on a GM vehicle as I only have Chrysler vehicles. My son used it on a 95 Camaro though but it was kinda strange as his 95 Camaro had an OBDII plug in it. But it is possible to retrieve OBD data with the MT2500. It all depends on what data GM made available in it’s control modules for that year. Email or text me a land line number and a good time to call. Contact info is in my signature below.

          #508666
          college mancollege man
          Moderator

            I don’t think you will get much sensor data.
            Most were just diagnostic codes.

            #508672
            A toyotakarlIts me
            Moderator

              Back in the day I used an ALLTEST 3256… You can get them dirt cheap nowadays… Tells you much more than you might think… I used mine predominately for GM’s made in the late 80’s… I still have it somewhere!

              Link to scanner on Ebay

              #508706
              Patrick O'ConnorPatrick O’Connor
              Participant

                [quote=”ToyotaKarl” post=54161]Back in the day I used an ALLTEST 3256… You can get them dirt cheap nowadays… Tells you much more than you might think… I used mine predominately for GM’s made in the late 80’s… I still have it somewhere!

                Can you give me an idea of what sort of info I might expect?

                #508781
                Patrick O'ConnorPatrick O’Connor
                Participant

                  ToyotaKarl,

                  I asked the ebay seller a similar question, and he responded,

                  “It will reveal stored codes as I understand it and tell you sensor values”

                  I also called the number that appeared on the front of the manual in the picture. I actually did reach someone at “Automotive Test Systems, Inc.” but they have no information for this older unit.

                  At least being able to read some of the sensor outputs could help with diagnosis.

                  #508804
                  A toyotakarlIts me
                  Moderator

                    OK I pulled out another old one I had, this was a 3250, but is pretty much the same thing.

                    Here is what it can tell you:

                    A/C Switch
                    Air Control
                    Air Flow
                    Air switch
                    Battery Voltage
                    Baro
                    Block learn
                    Booste wast
                    CCP Solenoid
                    Clear flood
                    coolant temp
                    Coolant fan

                    Crank
                    Cross count
                    Dwelll + RPM
                    EFE Solenoid
                    EGR %
                    EGR Pressure (V)
                    EGR Solenoid
                    EPR
                    EST
                    Exhaust Gas
                    Freon/Head
                    Gear 3/4

                    IAC
                    Igniyion
                    INJ Base PW
                    integrator
                    knock rtd
                    loop status
                    LV8
                    Man air temp
                    MAP/VAC (V)
                    MPH + TPS (V))
                    Nose switch
                    Oxygen (V)

                    Park/Neutral
                    Power Steer
                    Prom ID
                    Rear VAC BRK
                    Selection
                    SPK ADV RTD
                    Spark Count
                    TCC SOL + MPH
                    TPS (V) + RPM
                    Trouble Cd
                    Water INJ
                    WOT

                    When I used this, I used the Baro quite a bit as well as LOOP STATUS to check if the car was in OPEN or CLOSED Loop. Also you could check the O2 readings and see them switch back from lean and rich. Also used the TPS function A lot. Those computer controlled carbs had to be set just right…(anyone else remember this fun of drilling in the protective cover on the carb)

                    #508811
                    Patrick O'ConnorPatrick O’Connor
                    Participant

                      Wow, that’s a LOT of stuff! Especially considering the age of the car. OK, I’m convinced that it would be worth it to pick one up. I have a few different issued this could help me track town.

                      I guess we can’t make a blanket statement about what’s available informationwise for pre-OBD-II cars, but we do know that this particular car (and possibly most GM vehicles of this time) can tell you a lot through their ALDL connectors.

                      If anyone has a different conclusion or experience please let me know.

                      -PatrickO

                      #510357
                      Patrick O'ConnorPatrick O’Connor
                      Participant

                        OK, I bought the scanner, hooked it up to my car, but it won’t read any codes! Display lights up and goes through setup (cycles thru the numbers 82 to 86 for year selection), but then gives a blank display (four dashes) indicating either no data or wrong data type. Will this tool only work on 81 to 86 cars? (checked fuse in unit, fuse is good)

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