Speedometer calibration

[98chevy2500SS]

I adjusted the tire size setting with my Jet flash tuner to get my speedo to read rite. Then I swapped my cluster with a Denali cluster with the 120 MPH speedo. I had to adjust tire size again for it to read rite. The programmer is under $350.

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I might have to check into that. Thanks for the picture. I would love if both trucks' speedos read right.

 

[kennythewelder]

Summit racing has them in stock. Keep in mind that a dyno tune is more effective, but this is a handy tool to have.

I might have to check into that. Thanks for the picture. I would love if both trucks' speedos read right.

Only problem is, you can only use it on 1 truck at a time. It locks it self to the truck, and you can not use it on another truck with out putting the first truck back ti factory settings.

 

[RayHardesty187]

Hyper tech makes one as well. I'd just send the black box to black bear performance its cheaper plus they can adjust alot of things

 

[Insert Quarter]

Has anybody tried one of these?

https://www.lmctruck.com/1988-98-chevy-gmc/gps-speed-sending-unit

 

[gearheadE30]

Something to think about: My GPS speed and my PCM speed are within 0.6mph of each other across the entire sweep (5-85)... My speedometer is around 4mph fast, also across the entire sweep. All I'm going to do is pull the needle and reposition it, because that all I feel needs to be done. If I reprogram my PCM, then my speedo MAY be closer, but my odometer and PCM won't be anymore.

Are you sure that both your odometer was correct? My Limited's speedometer was off by nearly 10 mph because the tire size wasn't quite the same as original, and the odometer was off by nearly the same percentage.

There is also a parameter that you can change to adjust the speedometer output signal independently of the gear ratio/tire size part. That parameter is the key to keeping the PCM speed correct but also fixing the speedometer. I'm not sure why people always change the gear ratio parameter instead of the speedometer scaling parameter. I don't know which one the handheld tuners adjust. I did mine in EFILive, and I assume HPT is capable as well.

I adjusted the tire size setting with my Jet flash tuner to get my speedo to read rite. Then I swapped my cluster with a Denali cluster with the 120 MPH speedo. I had to adjust tire size again for it to read rite. The programmer is under $350.

That's surprising because the speedometer calibration isn't in the cluster - it is in the PCM. But it is possible that the 120mph clusters may be slightly different than 100mph or something.

 

[AK49BWL]

Are you sure that both your odometer was correct? My Limited's speedometer was off by nearly 10 mph because the tire size wasn't quite the same as original, and the odometer was off by nearly the same percentage.

10 miles driven according to the GPS equaled 10 miles on my odometer, so I would venture to say it's pretty accurate.

That's surprising because the speedometer calibration isn't in the cluster - it is in the PCM. But it is possible that the 120mph clusters may be slightly different than 100mph or something.

All 96+ calibration is in the PCM save for Diesels.

 

[DN7050]

I tried to get a local shop to calibrate the speedo with a tuner but they apparently didn't know how to do that so consulted with a speedp repair shop (in Tacoma, WA) who said the problem is a bad circuit board that had to be replaced for about $200. I called those guys too just to verify. Fortunately the shop didn't charge me for that effort and I went to a nearby "pick and pull" yard and found an instrument cluster from a very similar C2500 for $50. Installed that and the speedo is accurate. So my problem is fixed.