Speedo issue and tire fitment question on '91 Chevy

Discussion in 'Chevy C/K Truck Forum' started by CHoffman, May 11, 2009.

  1. CHoffman

    CHoffman New Member

    Hello all,
    I am having an issue with a recently purchased truck. It is a 1991 Chevy Cheyenne C1500 with a Muncie SM465 4-speed manual with the 4.3V6. I purchased it and had to pick it up on the other side of the state and on the return trip it worked wonderfully and made it here without a hiccup. Then all of the sudden the speedometer and odometer quit working. I checked the vehicle speed sensor and it tested a little low on resistance but replaced it anyway. That didn't work obviously. I didn't have much time to work on it today (the wife would have killed me being mothers day and all) but I did manage to visually inspect most of the wiring and completely disassembled the instrument cluster. The wiring looked fine and the cluster, although dusty, showed no signs of corrosion, burnt circuit board, or any other damage other than I may have to replace some of the bulbs later on. Next weekend or if I find time earlier I plan on doing a continuity test on all of the associated wires and a more complete visual just to rule wiring out. I am having issues finding the DRAC, speedo buffer, or whatever its called but have heard its in the cluster but I didn't see it. I am hoping its not the ECU or cluster but am not sure on how to test them. I've got a really good Fluke multimeter so if anyone knows how I sure would appreciate it. I have checked all fuses and they are fine and have also disconnected the battery for half an hour to clear the codes after replacing the VSS but still get a 24 code. I have found a schematic for the VSS circuit but am having issues finding the vehicle speed sensor buffer as I said earlier. I got my first speeding ticket in my 12 years of driving on the way to work last week so am kind of bummed my perfect record was ruined on account of not knowing how fast I'm going but oh well. That $90 would have been better spent on my truck IMHO but the trooper didn't see it that way :neutral:. Any help will be very appreciated. Thanks.

    Also I was wondering if some 31" tall tires on the stock 15" steelies will clear without rubbing on my truck. It is stock height and a regular cab long bed if that matters any. It looks like it will but would like to be sure before ordering them and hear from others who may have done this. Once again thanks for your time. I realize my speedo will be off roughly 4.1%, well that is if I ever get it working again :glasses:.
  2. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    I have a friend who's speedo quit working and he just pops his T-Mobile G1 up on the dash and uses a GPS program that displays his speed. If you have a Garmin or other GPS unit, you might have to do the same to prevent another ticket at least until you get the speedo repaired.

    The later model GM clusters had chronic problems. I don't know if anyone specializes in the earlier models.

    If all else fails, and you need to repair the cluster check out digi controls
  3. CHoffman

    CHoffman New Member

    Thanks for the link I saved it under my bookmarks just in case it does turn out to be the gauge. I just wish I knew how to test it to be sure. I don't have a GPS so I just pace traffic or drive much slower than usual now.
  4. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The DRAC units do go bad on these trucks. It can be hidden behind the glove box. First thing to do is get a wiring diagram. Then make sure you have a good ground <.300Mv or less> and battery voltage to the drac. Next check the AC signal from the speed sensor to the drac. Check it at the sensor first and then at the drac. The AC voltage should increase with wheel speed. Next check for a digital signal from the drac to the PCM. DC volts and Hz.on your meter.
  5. maxpower_454

    maxpower_454 Member

    You should have got it done on Sunday. Your wife isn't your mother......hopefully
  6. CHoffman

    CHoffman New Member

    maxpower_454- No, my wife isn't my mother. And judging from your response you aren't married as you would know your 'man badge' is revoked when you put on that ring:lol:.

    Jimmiee- I have learned that '91 was the last year that the DRAC was built into the circuit board inside of the instrument panel so that makes testing it extremely difficult. I think I may end up doing the swap to the later model gauges which involves a bit of wiring but I hope will be more maintenance friendly in the future. I've tested the voltage to the gauge panel and tomorrow will test voltage to the ecm. Would have done it today but got called in to work. It seems no one wants me to get this fixed or they would leave me alone for a good solid weekend.

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