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98 gmc different speedo problem

Discussion in 'Chevy Trucks' started by Catfishman, Oct 3, 2008.

  1. Catfishman

    Catfishman Junior Member
    Messages: 5

    Hi All
    I have been reading myself blind on every board I can find, but I still haven't found what I am looking for. I have a 98 GMC 3500 4x4 with 5.7l model:K30309 (I think that is right). My speedometer always reads faster than I am going, not wildly so like so many I have read about, but constantly. So 35 mph reads as 55, 45 reads as 70 and 55 reads as 85. I did (years ago put on different wheel and tires) but they are the factory sizes, so I don't think they could be the culprit (could be wrong though). I have replaced the VSS already and that made no difference.
    Could this be another incarnation of the step motor issues? Fuel pump sender?

    Please help. Redlining towards wits end.

    Thanks

    If you guys have already answered this 1K times please just point me to the thread.
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    First thing you need to do is determine whether its the speedo receiving the incorrect signal, or just the speedo head itself thats causing it to show the erroneous MPH.

    A scanner with live data readability will tell you. Plug the scanner in and take the truck for a drive and compare the MPH reading through the scanner with the MPH that the speedo is showing. This will help to get you pointed in the correct direction for further repair.
     
  3. Catfishman

    Catfishman Junior Member
    Messages: 5

    B&B thanks for the reply.
    Is there a scan tool that you recommend? I just bought a OBDII scan tool only to find out that almost exclusively covers the emissions stuff. I would like a real scan tool, but can not afford the few I have seen. I am not above buying used if you think that would be ok. I did try to run down the road and scan for codes at the same time, but still did not generate any codes.

    Thanks
     
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Thats the problem with so many of the inexpensive scan tools (don't mean code readers either)..there very basic. Scanners are like anything else you get what you pay for. For the DIY AutoXray makes some nice stuff thats reasonably priced for the DIY level if you want to look into them.

    Now if your talking a pro type scanner, personally I prefer OTC over the Snap on/Kal/Matco (whatever)... but thats probably more than your looking to spend. Although you can buy a new OTC Geynisis 2 with just the basic software (no ABS, Asian, air bag, TPMS, etc) for around $2000. I see used ones for sale from time to time, nothing wrong with a nice used one.
     
  5. Catfishman

    Catfishman Junior Member
    Messages: 5

    B & B
    Thanks for the info that is exactly what I was looking for. The code reader I bought is an autoxray, but it is the 700 (their most basic). I will start looking for a used Genesis 2.
    Is there anything else I can try in the mean time?

    Thanks you for all your help
     
  6. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Afraid not without a scanner, or at least not without using the shot gun method or I would have mentioned it.

    I just bought a used Genesis 1 (older model) that included some decent software to have as a backup at a local auction for $340 so I know there out there. Check Fleabay as well you can probably find some good used one on there.
     
  7. Catfishman

    Catfishman Junior Member
    Messages: 5

    OK thanks
    I will start saving my pennies and check around for a used one.

    Thanks again for the help.
     
  8. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Good luck with your hunt. :waving:
     
  9. 70monte

    70monte Senior Member
    Messages: 468

    I have an AutoXray EZ-Scan 6000, their top of the line scanner. Its a good scanner for the DIY and you can buy them new on Ebay for about $270 or so. I've had AutoXray scanners since 2000 and have always been happy with them.

    Wayne
     
  10. Catfishman

    Catfishman Junior Member
    Messages: 5

    70monte
    Thanks for the tip. Will the 6000 give you the data from the individual sensors?

    Thanks