2nd Gen Non-Engine/Transmission Canada truck, Speedometer off...rpm too?

[DHayden]

My truck came from Canada (sold new in Canada) and I bought it through a wholesaler in WA state. They changed the odometer, MPH over to US. I noticed a while back that I was passing people when I had the cruise set at the speed limit and found it somewhat strange (nobody drives the speed limit )



Anyway I checked the speed with my GPS and with the speedo reading 70mph I am actually going 75. 4mph. I was wonder how I can change this and if the rpm guage is effected also. As it is my truck doesnt seem to like it much above 2200-2300 rpm but really starts dropping off at 2400-2500rpm. Infact I have never taken it above 2500rpm because it just doesnt feel good.



With cruise set at 75mph (actual speed around 81) the rpm reads just under 2100 rpm. Does that sound close for what you guys are running? Any input is much appreciated.



Oh yeah, I have the 3. 54 gears

 

[johncameron]

what size tires are you running? At 2100RPM, you should be going 77MPH with 265's and the NV5600.

 

[DHayden]

I'm running Michelin 235's

 

[johncameron]

Ah, 235/85/16... 77MPH@2100RPM. That's what I run in the winter. I have no idea how to re-calibrate, but there is a problem!

JC



Somebody should know, this is a great place

 

[B.G. Smith]

Originally posted by

With cruise set at 75mph (actual speed around 81) the rpm reads just under 2100 rpm. Does that sound close for what you guys are running? Any input is much appreciated.



Oh yeah, I have the 3. 54 gears [/B]

You should turn about 2k at 70 mph. Sounds like the tach and speedo are off. The speedo is recalibrate in the pcm, I don't know if the tach can be recalibrated. bg

 

[DHayden]

2k rpm and 70mph with the 235's and my gear ratio? Is this based off your truck or have you tested it precisely?



No guru's out there that can wow me with numbers and give me some options?

 

[B.G. Smith]

Originally posted by DHayden

2k rpm and 70mph with the 235's and my gear ratio? Is this based off your truck or have you tested it precisely?



No guru's out there that can wow me with numbers and give me some options?

Yep, 235 Michelins, 2:54 gears, tested as recent as yesterday. I'm turning 2250 at 80 mph, I don't know how accurate my speedometer is though, I haven't checked it with GPS lately. bg

 

[bmoeller]

speed/rpm calculator

http://www.f-body.org/gears/

 

[DHayden]

Thanks bmoeller, looks like my rpm is off by 100 and my speedo is off by around 4 mph. Seems to corralate, wonder if it's an easy fix? You guys think they put the needles back on wrong? I dont know what else is involved but maybe adjusting the needles will work

 

[B.G. Smith]

I don't know how accurate the tachometers are, you did notice that the graduations are in 125 rpm increments? I would guess the tach. is getting it's info from the crank position sensor through the PCM(power control module computer). The speedometer picks up it's signal from the sensor in the differential and it also goes through the PCM. To recalibrate the speedometer for tire diameter/gear ratio etc. changes, the PCM has to be reprogramed by someone with the proper equipment. bg