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vehicle speed sensor question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Rustbucket, Jun 8, 2003.

  1. Rustbucket

    Rustbucket Registered Member

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    I have a 91 blazer with the 700r4 and np 241 x-case. I had some transfer case problems a while back and fixed those. Ever since then, my check engine light comes on till I hit about 35 mph, then it goes off and my brake light comes on. The brakes don't work like they should until the brake light comes on. I'm getting the code for the vss. Also, my speedometer bounces and sometimes doesn't work at all. From what I gather, the VSS is for the ABS system. If this is true, will I have any problems with my 3/4 swap next week? I wouldn't mind getting rid of ABS stuff while swapping, it doesn't work anyway. I did a search, but no one had all the same symptoms as I do. Thanks in advance for any help you guys can give me on this.
     
  2. HarryH3

    HarryH3 1 ton status Author

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    As a point of background, a '91 doesn't have a speedo cable. Instead, the speedo is driven electrically from the VSS (Vehicle Speed Sensor). It generates pulses that are directly proportional to the speed of the vehicle. The bouncing speedo suggests that the VSS connector may not be connected tightly since the work was done to the t-case. The engine control computer also uses the VSS signal, as does the anti-lock brake system. Check the plug at the tail end of the t-case and make sure it's plugged in all the way and that none of the wires froom it are touching the exhaust system. Once you get the signal going to the computers again, the problems should go away. /forums/images/graemlins/thumb.gif
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    I have not messed with a 241 but there should be a "Tone Ring" that the VSS picks up off of. I think these can be installed backwards I read somewhere.
    If you don't find a obvious wire problem pull the VSS and look in the hole for the tone ring. These are usualy about 1/8inch from the VSS. If it was installed backwards it will be a greater distance and you will not get a strong VSS signal if one at all. The computer sounds like it went into Limp home mode is why everything started working "Better" once you cleared 35MPH.
     
  4. TravisO

    TravisO 1/2 ton status

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    I had a similar problem, but not exactly the same. I was wheelin' and my check engine light started coming on. Later I realized my speedo wasn't working (I have a '91 also). Crawled underneath to find the VSS cable had been pinched and sheared off. At the time I had no idea why. The two leads that go to the t-case were shorting together and causing weird feedback to the computer. Turning the ignition off and then back on would make it go away for a while, but then it would come back on.
    Started hearing a clunking noise later on the same trail ride, but every time I looked underneath at all the suspension components everything seemed fine. Then I tried to check the driveline u-joints by twisting them and shaking the driveline. The whole t-case slopped back and forth on the crossmember! Moved several inches in both directions. So the VSS cable must have got pinched between the t-case and exhaust. I'll be replacing the rubber tranny mount with some stronger urethane.
    Travis
     
  5. K5 NUTT

    K5 NUTT 1/2 ton status

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    Ok...here it goes...vss to drac...drac to ecm...cc module..abs ecu..speedo.

    Vss generates a/c voltage...jack up rear wheels and support on stands...there is a break in the vss harness on the left side of the tcase...put in drive and crawl back under there and unplug the harness and check output voltage with a good autoranging dvom...reading should be .300 and up to 1 volt a/c depending on wheel speed....now plug it back in and open the glove box...all the way down...there is a break out harness for the vss and such right in front of the heater box...actually there are two but one goes to the aldl connector...you are looking for two wires...one is green/black...and the other is pnk/black...these are the vss wires before they go to the drac module located underneath the radio...if you are still getting a reading and this connector its time to pull the dash bezel and remove the radio...underneath the radio there will be a white box called the drac...it buffers the a/c volts from a round wave to a square wave pattern and adjusts the signal for tire size and rear end ratio...not automatically though...and if the siganl is present at the same two wires at the drac module its time to get a new drac...which is not ava at the dealership...nor is the speedo head...ISS (Instrument Sales-www.instrumentsales.com)will sell you a new one burned for your tire size and rear end ratio for $85 to your door...they will need the rear end ratio and the circumfrance of the tire to properly burn the drac.

    I just replaced the vss in our 90 V2500 yesterday...there are allmost $100 thru gm...$75 or so at napa...

    DW
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    Ok...here it goes...vss to drac...drac to ecm...cc module..abs ecu..speedo.

    Vss generates a/c voltage...jack up rear wheels and support on stands...there is a break in the vss harness on the left side of the tcase...put in drive and crawl back under there and unplug the harness and check output voltage with a good autoranging dvom...reading should be .300 and up to 1 volt a/c depending on wheel speed....now plug it back in and open the glove box...all the way down...there is a break out harness for the vss and such right in front of the heater box...actually there are two but one goes to the aldl connector...you are looking for two wires...one is green/black...and the other is pnk/black...these are the vss wires before they go to the drac module located underneath the radio...if you are still getting a reading and this connector its time to pull the dash bezel and remove the radio...underneath the radio there will be a white box called the drac...it buffers the a/c volts from a round wave to a square wave pattern and adjusts the signal for tire size and rear end ratio...not automatically though...and if the siganl is present at the same two wires at the drac module its time to get a new drac...which is not ava at the dealership...nor is the speedo head...ISS (Instrument Sales-www.instrumentsales.com)will sell you a new one burned for your tire size and rear end ratio for $85 to your door...they will need the rear end ratio and the circumfrance of the tire to properly burn the drac.

    I just replaced the vss in our 90 V2500 yesterday...there are allmost $100 thru gm...$75 or so at napa...

    DW

    [/ QUOTE ]
    So when are you going to do a detailed write up?

    I'm about to get into this mess myself.
     
  7. mosesburb

    mosesburb For Rent Premium Member GMOTM Winner

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    Man, you sure make it sound like you know what you're doing /forums/images/graemlins/rotfl.gif.
     
  8. BurbinOR

    BurbinOR 3/4 ton status

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    He does..........he's da man! /forums/images/graemlins/thumb.gif
     
  9. K5 NUTT

    K5 NUTT 1/2 ton status

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    I have absolutely no clue how to do a write up with pics and all...funny though...i can fix this stuff...but html is over my head...lol.

    DW
     
  10. K5 NUTT

    K5 NUTT 1/2 ton status

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    Ocassionaly i even surprise myself nick...lol.

    And frank...in the spirit of things...i finally scrounged a set of factory low backs and a year later they are recovered and mounted...so the high backs from you many moons ago went to a fellow k5 owner here in town for free...carry'n on the ck5 tradition....thanx frank!!!

    BTW frank...what kinda mileage do you get with that 4L80E equipt V2500????? Momma drove hers for the first time last night and today is the first day of DD duty for her....she loves it...except the small problem of her learning how to back it up out of a stall at walmart tonight...its what happens after 12 years of rice...Honda civic SI....lol.

    DW
     
  11. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Take pictures of the important stuff. Write a story in Word. Make note of where the picture goes. Send it to me and I'll post it for you /forums/images/graemlins/smile.gif
     
  12. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    except the small problem of her learning how to back it up out of a stall at walmart tonight...

    [/ QUOTE ]
    I feel her pain! /forums/images/graemlins/wink.gif The first time you drive a Sub, it feels like you're captain of an oil tanker. /forums/images/graemlins/eek.gif But once my wife learned to park our '94 Sub then it wasn't mine any longer... /forums/images/graemlins/frown.gif She loves being able to put the kids and all their toys in the Sub with ease. /forums/images/graemlins/thumb.gif
     
  13. K5 NUTT

    K5 NUTT 1/2 ton status

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    Well grimy my friend...when i find some time i'll take some pics...not to familiar with word...but i think i know what that program is..

    DW
     
  14. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Any word processor program will work. Then just cut an paste it into a post or e-mail it to me and I'll post it for you.

    Just go step by step, Mention key points along the way. Make a list of sources for parts you used.
     
  15. emoo99

    emoo99 1/2 ton status

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    wheres the write-up?:whistle: :pimp:
     

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