I was trying to measure my "fuel economy" mpg, and noticed that my odomoter is way off. I compared the odomoter indications to the milemarkers along side the freeway over a 10-mile stretch and discovered about a 65% odomoter error. Odometer reads 16 miles when I've only gone 10. My speedometer seems reasonably close, since I'm going about the same as other cars and the speedometer indicated speed sounds reasonable (it sure as heck isn't 65% off) and I'm not getting ticketed, or having to drive in the slow lane. It's a'90 IROC, so I'm pretty sure it's a VSS and not cable. just wondering if I inadvertently messed something up while modifying my BINs.

or does the odometer normally read Kilometers instead of miles. this isn't a european or canadian car.

 

the odometer works directly off of the speedometer, so im guessing, the speedometer is really off, and then your needle is off as well, maybe in the way that its actually showing close to your real speed, but behind it, its quite off. make sensE?

 

yep that makes sense. I guess my real question, which you answered, was whether the odometer had a separate input signal independent of the speedometer, and I suspected it didn't., but wanted a 2nd opinion.

thanks.

 

Have you changed gears or tire size??

 

I haven't changed rear-end gears. it's the 9-bolt Borg-Warner rear end, which should explain that. Actually, I'm okay with the stock rear-end ratio since 1st gear with the TH700R4 is so darn steep. It's my daily driver, gets me to/from work.

I did change the rear tires from the stock 245/50/16 to 255/50/16 to get more rubber meeting the road with the stock rims since "breaking traction" was a little too simple (every little bit helps), but that by itself does not result in a large speedometer error. I'm thinking a few percent, certainly not 65%.

I forgot to mention in my earlier posting that I do use DataMaster to log data, and according to DM, my speedometer is indicating "close-enough" with what DataMaster is showing the VSS indicates.

Therefore, I'll have to reluctantly conclude that my odometer is screwed up, although the 1/10th's roll over smoothly, not indicating missing internal odometer gear teeth which of course makes me not want to believe that it's hosed. oh well.

 

http://www.tbichips.com/drac/

 

belatedly, I discovered my odometer is metric, kilometers.

another camaro-dude asked if my car was export, "huh, what?" I thought he was talking tail-lights.

my speedometer has 240km/h in bright yellow, and within that it goes up to 145 mph in subdued blue. the inverse color scheme of domestic speedometers, I guess. I hadn't really paid attention to speedometer color schemes, I thought that was normal with GM's halfway attempt at going metric back then.

odometer is 7 digits (including the tenths). it never occurred to me that it would be metric.

no wonder it's sixty-something percent off. gee whiz. duh.

now I'm wondering what's an export 5.7L car doing in Hawaii...

well, I've got 220,000 KILOMETERS which now ain't that much.

 

Wow, that's actually pretty cool...

 

The odometer is "right", if anything is. It's nothing but an event counter. All it knows, is to count pulses; 2000 or 4000 pulses, whichever version you have, = 1 mile. MUCH harder to screw that up than the speedo.

Drive a measured stretch of highway at a constant speed on the speedo; say, 10 miles at 60 mph. Time it. 10 miles @ 60 mph = 10 min. If your time comes out more than a few seconds different from that, then your speedo is off.

Sounds to me rather like your rear gear has been changed, but your speedo gear has not; and somebody has just wacked on the programming to reduce the more obvious appearance of error.

 

the car was bone-stock when I got it. original rear end, no gear swaps. When I swapped the tranny, I pulled the tailshaft housing to pull the wheel off the outputshaft, and transferred the VSS.

the speedometer reads okay, I've had the opportunity to compare it with different "references" and it sure as heck isn't 60% out-of-whack.

other threads on this site confirm the "export metric odometer".

I've futzed with the ECM programming myself, but didn't touch the speedometer or VSS areas. I've compared my "bin" with the factory "bin" to make sure I'm tracking.

I've stopped pondering.