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“Pre-OBD” Diagnostics

This topic contains 9 replies, has 5 voices, and was last updated by Avatar Patrick O’Connor 7 years ago.

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  • #508607
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    Patrick 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

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  • #508609
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    dave
    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
    Avatar
    John 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
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    college man
    Moderator

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

    #508672
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    Its 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
    Avatar
    Patrick 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
    Avatar
    Patrick 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
    Avatar
    Its 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
    Avatar
    Patrick 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
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    Patrick 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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