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Re: Non-linear speedometer error [message #370670 is a reply to message #370652] Mon, 10 October 2022 08:14 Go to previous messageGo to previous message
RF_Burns is currently offline  RF_Burns   Canada
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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Senior Member
TomK,
The EBL has a VSS-Pulse per mile parameter (6th entry from the top in TunerPro) that you can adjust to set the WUD speedometer. I had adjusted that parameter to match GPS speed long ago, so I just multiplied that number by 1.114 and came up with 2224.44. It seems to be close to GPS, but I'll need to test it when the dog is not with me. Dog and laptop are not compatible in the same space beside me!. Also check the setting of the VSS filter. It smooths the speed reading. I noticed several years ago that my engine would randomly cut-out. I then noticed the WUD speedo was jumping up by 40-50kms. Turns out it was the Over-Speed parameter causing the engine to cut-out. My VSS sensor had a noisy reed switch causing extra pulses. Replacing the reed switch fixed it. RandyV then told me about the VSS-Filter, so I raised it to 75.

Matt,
Thanks for your info on calibration. Since the error percentage seems to increase with speed, I was thinking maybe the needle spring has weaken. Or maybe bearing, or 45 years of dust accumulation has increased a slight bit of physical drag. This past summer the needle would jump up in speed. I found the cable was not tight at the transmission, but seemed to turn freely. I didn't notice it "jumping" on this trip. Could be just things are worn and dragging.

Larry,
I plan to do some tests with Paula recording the data. Your plan seems a viable way to keep the old speedo, however I'm not sure I'm good enough at graphics to pull that off. I'm an electronics guy so I could replace the mechanical guts with a stepper motor.

I don't really want to replace the speedo with a new one because I'll loose the PRNDL indicator. Non of the replacement speedos I've seen have that.

Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

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