Speedometer error

[aldive]

I am having a speedometer error problem.

When comparing actual speed ( via GPS ) to indicated dpeed ( on speedometer ), the indicated speed is 8-9 MPH higher than actual. Yhe odometer appears accurate.

Ideas and suggestions to fix are requested.

Thanks ....

 

[Eneurb]

Do you have the proper size tires and gears?? Have you ever had the pcm recalibrated for a different gear or tire size?? If the odometer is accurate, the speedo. itself is at fault. Be aware that factory spedometers can be off by as much as 10% above the actual vehicle speed to help prevent manufactorer liablility for speeding.

 

[CDW6212R]

That could explain why my 30.5" tires haven't shown hardly any error.

Al, do you not have any radar machines along the road in your area? Often there are radar machines in construction zones. The PCM chips and flashers can adjust the speedometer also. Good luck,
DonW

 

[ExplorerDMB]

Aldive - I have a similar problem. I do have a bigger tire size than stock, but I put in a gear ratio that is more than equivalent to stock. I have a 4.56 gear ratio wtih 33" tall tires and I believe that 4.10 would of made me "stock" again, yet my speedo is off 3mph (from 0-30), off 5mph (30-50), and off by about 7mph (50-70). 70mph is the fastest I go with SSRs ha. But uhh...yeah I used a friends GPS system and thats what it told me yet I was driving down a road one day with a police speed reader thing in front of me and it was pretty close to the speed that was indicated on my speedometer. So I might at work hook up our OBD scanners and just watch what the PCM is reading. I won't be able to do it very soon, but once I do I will let you know.

-Drew

 

[huskyfan23]

I wouldn't trust the GPS over your speedo.. it's not tapped into the VSS so it's just making predictions.

 

[aldive]

I wouldn't trust the GPS over your speedo.. it's not tapped into the VSS so it's just making predictions.

GPS is the most accurate way to measure speed, period.

 

[CDW6212R]

Okay, without arguing about the accuracy of the GPS systems, what do the police use?
What standard is more important, the radar, which determines whether you get a ticket, or GPS.
If speeding isn't an issue, then accuracy would be my highest goal. LOL,
DonW

 

[huskyfan23]

If you say so.. I guess the only way to know for sure is to go by one of the police radar screens or get a guy with a radar gun.

 

[MazdaGreg]

The police cars also what's called "Calibrated" Speedometers. These were camaro's that used to come into my dealership. Don't know why all speedometers are calibrated, but theirs are. The way you distinguish is they say "Calibrated" along the bottom of the Speedo.

Sucks, because we can be following our speedo's, and they can still bust us...

 

[huskyfan23]

My digital speedo is dead-on with those roadside radars so I'm safe

 

[Mbrooks420]

In both my Explorers the speedo's have been dead accurate with the roadside radar signs from 30 to as high as 83. The speedo may have too much drag in itself, and may be trying to read the correct speed. Otherwise the odometer would be off equally. Does it reach the bottom of the gauge before 10 miles an hour? Maybe the needle needs indexed.

 

[Charlie's_93EB]

i do not know if this is sad or not but i have done this.

both my dad and my self have driven with dual GPSes, while driven in front of the city's "your speed is thing".

-both are garmin and almost always are in one tenth of a mph of each other and is about the same as the city's thing,(within a mph).

-And my Ex and my dad's buick are about 3 mph slower then the car's speedo @ 30mph, so either the city and both gpses are wrong or the Ex is.

what do you think?

 

[CDW6212R]

Yes, there is error in everything. If we drive on the high side of the speed limit, then what matters is the accuracy of what we are going by, AND the accuracy of each police officer's device.

I had a 1986 police Crown Vic, and at about 200,000 miles, the speedometer was reading slow, while the odometer was fine. The mechanical speedometers run off of air friction. If there is anything, oil or dirt, in the air gap, the speedometer may read higher. If there is extra drag, say from age, then it will read slow. I don't know about our electronic speedos. I will be adjusting the mileage on the newer cluster that I am adding. I will see then. LOL,
Don

 

[Crankcase]

Have any pics of that Police Crown vic? Did it have the guages on the passenger side also?

 

[CDW6212R]

Crankcase, what gauges? I sold the 86 to the son of my best friend at 235k, and he died in it, wrapping it around a pole.
I bought the two 95's the same week at auctions, planning to make a good delivery vehicle from one. After choosing the tighter car(98k), I added ABS, Town Car seats, an extra relay box, overhead console(3 gauges), strobe lights, trunk power outlets, new front control arms, 16" aluminum Crown Vic wheels, new paint, windshield, remote starter, right side turn signal control, aftermarket stereo, etc.

The newer Crown Vics are harder to drive from the right seat than the older body style. It is harder to reach the pedals, and out of the right window to deliver mail. I have been working towards a dedicated Explorer for full time use.
DonW

 

[Crankcase]

You made one a right hand drive or something? Pics needed!

Uh, sorry to hear about your friend........


The old police Crown vics had 3 guages mounted on a pod just right of the clock.That way they had idiot lights AND guages.

 

[CDW6212R]

Yes, some did have extra gauges, my 86 wasn't a patrol car.
I drive them all from the right side, so I don't have extra stuff in my way in front of me.
Don