Speedo calibration
 

Can speedometer be reprogramed with tunerpro?
I have tried to change 4000 pulses/mile but it only changes
speed that ECM see, not LCD display reading.
What is this used for?
http://i31.tinypic.com/2mmg3n9.jpg

Car is '90 Corvette with 727 ECM. I'm using Super $8D definition file.

Re: Speedo calibration
 

This is a good question.

I think the '727 sends a 2000 PPM signal to the CCM.

This needs more clarification. I'm going to dig a little deeper, but hopefully some of the experts will chime in.

-- Joe

Re: Speedo calibration
 

There are three bits (5, 6, 7) in word 8014 that are divisors for the pulses in hardware. The ECM does not see this according to some old notes from Ludis. (Where i found the info)
The S_AUJP V4 definition has them in it.
I have never adjusted to see what effect they had on the outputs (I don't have dash or cruise)
There are only a handful of possibilities that seem to be for high output count optical sensors, If this is to correct for a rear gear or tire change, A DRAC fix or trans gear would most likely be needed. The settings indicate they divide to obtain the 4000 PPM the ECM is looking for.

Here is the table A = b7, B = b6, C = b5
I found this somewhere in the DIY-EFI archives that Ludis Langens posted about years ago.
That guy deserves alot of credit for the work he did on the hardware schematics and info he brought to the surface.

A B C
0 0 0 Divide by 1 (ie for a 4000 ppm VSS)
0 0 1 Divide by 9 (36000 ppm VSS)
0 1 0 Divide by 7 (28000 ppm VSS)
0 1 1 Divide by 11 (44000 ppm VSS)
1 0 0 Divide by 6 (24000 ppm VSS)
1 0 1 Divide by 10 (40000 ppm VSS)
1 1 0 Divide by 8 (32000 ppm VSS)
1 1 1 Divisor disabled, no output

Also do a search for "VSS scaling "
There was another member 92Z-666, who did some investigation while changing the bits and documenting the results.
Found a link to the info:
http://www.eecis.udel.edu/~dzug/92z2...0-vss4T56.html
Enjoy :-)

Re: Speedo calibration
 

Is he still around?

Off topic, but thought i'd ask you. Can CCM's data be altered by reading and reburning with a prom burner? I.e, my car has 120k on it. If I do a dash swap with a CCM that has 93k on it, how do I advance the miles to 120k? I don't want an RMV issue when I get a new inspection sticker.

-- Joe

Re: Speedo calibration
 

No idea, He seemed to be around before my time.
I have certainly benifited from his leg work, I always try to give credit where due.
As far as the CCM goes, IDK. Haven't done anything with them.
Pretty much just swearing at the BCM in the wife's Caddy when it doesn't cooperate.