speedometer off

**wvbrett** · 06-04-2011, 01:02 PM

ok so the speedo on my 2000 t/a 5.7L m6 gets more and more off the faster i go. at 35 mph i am about 3 mph off. but at 70mph on my gps i am only going 55mph on my speedo. it has stock 3.42 gears and stock tire and wheel sizes. i am guessing something has gone bad i.e a sensor or something. however, i am not too familar with this system and my hanes manual doesn't go into the speedo.

so what do i need to look at and where are the things i need to look at. any troubleshooting tips or suggestions of how to figure this issue out?

**Y2KPewterSS** · 06-04-2011, 01:09 PM

Originally Posted by wvbrett

ok so the speedo on my 2000 t/a 5.7L m6 gets more and more off the faster i go. at 35 mph i am about 3 mph off. but at 70mph on my gps i am only going 55mph on my speedo. it has stock 3.42 gears and stock tire and wheel sizes. i am guessing something has gone bad i.e a sensor or something. however, i am not too familar with this system and my hanes manual doesn't go into the speedo.

so what do i need to look at and where are the things i need to look at. any troubleshooting tips or suggestions of how to figure this issue out?

Just a thought here, are you sure your GPS is accurate?

**2001NBMZ28** · 06-04-2011, 03:59 PM

Get someone next to you on the highway at 70 and tell us what your RPM is at the same speed in 6th.

**wvbrett** · 06-04-2011, 09:02 PM

when i bought this thing my buddy drove my 2010 f-150 back. i called him, as he was following me, and asked what i was going in my truck. he said 70mph. so my gps is accurate. i'll check again, but my rpm's at 70 (according to the gps and truck) were right around 1500 in 6th gear i do believe.

**Ant71130** · 06-06-2011, 04:36 AM

Originally Posted by wvbrett

ok so the speedo on my 2000 t/a 5.7L m6 gets more and more off the faster i go. at 35 mph i am about 3 mph off. but at 70mph on my gps i am only going 55mph on my speedo. it has stock 3.42 gears and stock tire and wheel sizes. i am guessing something has gone bad i.e a sensor or something. however, i am not too familar with this system and my hanes manual doesn't go into the speedo.

so what do i need to look at and where are the things i need to look at. any troubleshooting tips or suggestions of how to figure this issue out?

Had a similar issue once. First thing, are you sure it haas the stock gears? You're probably right, but my next question would be, how many previous owners? Are you positive the guy before you didn't change the rim/tire size and then the dealer switch them back? My speedo was off when I bought my car as well, more so the faster I went obviously and my mom was wondering why I was going 50 the whole way home when I tried going 70-75. It was a 12 hour drive lol. My point being, I called the dealer and had them look up the previous owner, apparently he had put 20" rims on it and the dealer guy replaced them back to 17"s. Which is fantastic because imo it would have looked horrid with 20s but, moral of the story, it wasn't recalibrated/tuned afterwards. That's the only reason I bought my handheld tuner, in case I needed to change that or rpm limits, things of that nature. Might be worth looking into. The car's past I mean.

**Whamhammer** · 06-06-2011, 09:30 AM

WHat you might want to try doing is test the speed at incriments of 5 mph with a friend and not the variance in speeds shown. Then do some division to figure what the percentages of the variances are. If the variance is consistant, reprogram the pcm to compensate. I'd give it a plus/minus factor to take into account tire wear, etc.