Anyone know how to correct speedo error my 88 Formula with a 4.9 Cad engine and auto trans with 225/45r17 Mich run flats is running 7 miles /hour fast at 75 miles / hour I can't find anyone to correct it i9n the Tucson Phoenix area . Help

quote Originally posted by 2268irma: Anyone know how to correct speedo error my 88 Formula with a 4.9 Cad engine and auto trans with 225/45r17 Mich run flats is running 7 miles /hour fast at 75 miles / hour I can't find anyone to correct it i9n the Tucson Phoenix area . Help

have a cop ether follow you and clock your speed or hit you with a radar gun while you are driving at a certain speed by you speedo, you can also send the speedo into a shop to have it certified, not cheap and they will need to know lots of info about your car tires and trany I believe.

not sure how far you are from this place but give them a call.

http://www.dicksspeedotach.com/

there's also this place in Tuscon

http://www.yellowpages.com/...11?lid=1000309256256

Steve

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Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

[This message has been edited by 84fiero123 (edited 05-19-2014).]

are you sure the vss gear is correct? i read a ton of info and specific threads related to spedo gears and transmissions/rear ends/tire sizes etc. when i had speedo problems. there are at least 3 different plastic color gears.probably you have the wrong one, or you can compensate by getting different one for your "off" .

I called the Cadillac dealer and he thought you have to flash the computer . What is the vss gear and where is it located in the trans?

dont know how it works exactly but on an auto it is below the alternator with 2 wires and metal clips to hold it in place. the different gears tell the speedo about revolutions which are determined and affected by things like different tire sizes/gearing etc. you can probably just try different ones that have different amount of teeth until your gauge is accurate.

There is no speedo gear on the 4T60E. It uses a magnetic pick up with a reluctor ring set up for 24,000 PPM (Pulses Per Mile). No you can't get a reluctor ring cut witha different number of teeth. The ECM needs to be programmed for the actual PPM input. This can be done by the person who programmed your ECM. Hit me up if you don't have someone who did your programming.

4T60E VSS pick up


Not the 4T60E reluctor ring but a generic example


The 4.9 Caddy ECM uses a PROM chip, not flash programming. The plus on this is that you can 'reprogram' your ECM by swapping the chip. Flash programming would have required you to send the ECM to someone to have it programmed.

My emai if you don't have someone else to program the ECMl - gofast@reddevilriver.com

[This message has been edited by phonedawgz (edited 05-21-2014).]

sorry,
i was talking about fiero speedos, thanks for giving corrected info phonedawg.

Fiero speedo correction is very simple. Remove the plastic lens on the cluster. Slip off the speedo needle...it just pulls straight off. Use or borrow a GPS and go up to say 60 mph (middle of the band)on the freeway and hold it steady while you push the needle back on to match the reading on the GPS. Then in the normal driving range of 35-70 its very accurate. It just is off more than a mile or two under 35 or over 80...and in either of those cases, its not that important anyway. Works everytime and requires no parts or dismantling anything. I did all 3 of mine. I reset false reading gas gauges the same way...I just reinstall the needle when its almost completely empty. You dont need to know when its over full.

great tip, roger. thanks

Im assuming the speedo works, just dont read correctly.....

quote Originally posted by rogergarrison: Fiero speedo correction is very simple. Remove the plastic lens on the cluster. Slip off the speedo needle...it just pulls straight off. Use or borrow a GPS and go up to say 60 mph (middle of the band)on the freeway and hold it steady while you push the needle back on to match the reading on the GPS. Then in the normal driving range of 35-70 its very accurate. It just is off more than a mile or two under 35 or over 80...and in either of those cases, its not that important anyway. Works everytime and requires no parts or dismantling anything. I did all 3 of mine. I reset false reading gas gauges the same way...I just reinstall the needle when its almost completely empty. You dont need to know when its over full.

Old School Rules.

Steve