Speedometer HELP!

[mfewtrail]

IF what "GhrarhG" pointed out turns out to be true, what would should be focused in on?

Here's an old post that touches on what GhrarhG mentioned:
http://www.tgpforums.com/index.php/topic,2708.0.html

[TGed]

I will forward this to the guy. 

Thank you.

[TGed]

I think the cluster reads right now (thanks to that link) .  Might be 2-3 mph off still, but the laptop should see corrected speedo still. 
I guess GM never has put 100% effort into there development.  lol

My friend said the guy went with a "factor of 9 which is decimal "32"."

[TGed]

Apparently it's still off, but only by 5 mph (cluster reading 5 faster than actual speeds) .  The datalog is on par though.

[GhrarhG]

Sorry about falling off the map. Been so busy I haven't even had time to work on tuning my car.  There are two different constants one to get the ECM right, and another to get the cluster to match. There are different cluster constants for different clusters.

The reason I asked if it was off the whole way by 15 or if it was off by 15 at high speed and less at low speed was that if the error changes with speed it's a percentage error. As in you have a constant that is wrong. If you're off by 20% at 30mph it's only 6mph off, but at 75 the error is 15mph. If the datalog is correct you have the road speed sensor constant correct. Just try changing the IP Pulse Divisor to get the gauge to match. I had some trouble with that, as it seemed to change minimally and then jump.

Good Luck

[TGed]

Pretty much now his cluster is 5 mph off from 20-60 that he knows.  I guess he'll try going 70-80 to make sure. 

We thank you GhrarhG