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Thread: Having problems connecting via ALDL with 8625 PCM

  1. #1
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    Having problems connecting via ALDL with 8625 PCM

    Back sometime ago, I asked a similar question and Dave W provided an answer which was to move ALDL wire from Pin E to Pin M. I recently did this by cutting the wire and attaching male and female connectors. The net effect has been "no go". I have access to a SnapOn MODIS scanner and the resulting message is unable to connect/communicate. I am not able to read anything which signifies no connection.

    I am running a self-made ECM-to-PCM adapter between my stock harness and an 8625 PCM. Any thoughts/suggestions?

  2. #2
    Super Moderator dave w's Avatar
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    I would take a second look at the ALDL wiring. The '8625 only uses 3 wires to the ALDL; pin A, pin B, and pin M. Remove the unused wires from the ALDL.

    It sometimes causes confusion with scan tools, select a 1993 '8625 $E6 vehicle by make / model / year / engine / trans. For example 1993 / GMC / K1500 / 5.7 liter / 4l60E Vin code K. The vehicle you choose might need to be different if your using $OD, $OE, or $31.

    dave w

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    Happy New Year to you Dave W!

    Thank you for responding and providing the insight to using a scanner. The main reason I used connectors versus pulling and re-positioning the unused ALDL wires is I could not remove the white, plastic retaining clip. Do you have a gimmick or know of a method to remove the clip without obliterating it? Thanks in advance.

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    Super Moderator dave w's Avatar
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    One option would be to get an ALDL connector from a salvage yard vehicle that has Pins A, B, & C, to replace the existing ALDL connector. Remembering to connect old Pin E to new Pin M.

    dave w

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    Dave,

    Am I correct to interpret your response to say there is no easy way to remove the retaining clip without damage? Okay. To ease my salvage yard adventures and search, are OBDI connectors limited to only GM manufactured vehicles in specific years or did other automakers also install them?

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    Super Moderator dave w's Avatar
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    Yes, GM only. Most all 1990 - 1995 (except maybe some 1995 LT1 GM vehicles) Buick, Olds, Pontiac, Chevy, GMC, and even Cadillac will have the OBD1 ALDL connector with pins A, B, & M. Chevy and GMC pickups starting in 1993. I'm betting your going to be able to find what you need at any salvage yard that has domestic GM vehicles 1990 - 1995 You will likely never ever have a such an easy and readily available salvage part to search for again!!!

    dave w

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    Thanks DaveW. I hope you are right about my search being an easy one. Unfortunately, being in the middle of the Pacific, that sometimes may not be true.

    Is the wiring actually different between the ALDL and the square OBDII?

  8. #8
    Super Moderator dave w's Avatar
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    Quote Originally Posted by 57 Handyman View Post
    Is the wiring actually different between the ALDL and the square OBDII?
    OBDII started in 1996, and has different wiring.

    OBDI ALDL with 160 Baud will use Pin E.
    OBDI ALDL with 8192 Baud will use Pin M.

    Generally GM passenger cars started using OBD1 ALDL Pin M with 8192 Baud in 1990.
    Generally GM Light Trucks started using OBD1 ALDL Pin M with 8192 Baud in 1993.

    The 16168625 computer is OBDI ALDL Pin M with 8192 Baud.

    I'm very fortunate to live in an area with several salvage yards close by. I sometimes overlook that some members are not nearly as fortunate with salvage yard selection as I am. What is likely less than a 5 minute part search in a salvage where I live, could be a nightmare to find for some members.

    dave w

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    is a 16144288 ecm a 8192 baud?

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    Happy New Year, Anthony!

    From all that I've read and am aware, 4288's are S_LL_OOO_WWWW at 160 baud. The difference in processing speeds between black connectors ECMs and red/blue PCMs was my main reason for opting to go 8625 PCM. However, the side-track foray we took with the 7747 ECM was beneficial to determine the sensors and existing systems, i.e., ignition, fuel pump/relay/regulator, etc. were operating properly.
    Last edited by 57 Handyman; 6 Days Ago at 12:07 PM.

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    handy is your calpac for a v6/4.3? I have one for a 427 pcm but it is a 4.3 std trans if you need it.

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    Thanks for the offer, Anthony. If I remember correctly, my 8625 was from a '93 4.3L Sierra. Yes, it does have a memcal with .bin chip and netres.

  13. #13
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    DaveW, thanks for the information. Rather than cutting the wires and isolating Pins A, B, and E via M location, I fashioned separate jumper wires to connect the ALDL to the AutoProm. I'm now able to emulate.

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