Tach and Speedometer don't mach code reader?

[1MITCH1]

My tach reads 3-500 rpm lower than what the OBDII reader says. I know the tach gets it's signal from the alternator, there are no other signs of alt problems.
The speedo is within 1-2 mph of two different gps units even though I'm on 32"s, but the code reader shows vehicle speed 5-7 mph slower.
Otherwise it runs about like you would expect a 19 year-old Rover to run. Are these signs of impending doom, or should I not worry about it?

 

[robertf]

That's how they acted from the showroom floor

The speedo is about 10% fast so 235s fix the problem

 

[stu454]

...The speedo is about 10% fast so 235s fix the problem

Ha. I guess that explains the speedo on my D1 on 235's.

 

[1MITCH1]

But why does the ecu report road speed so much slower? Do they not both get their signal from the VSS?

 

[robertf]

Because the ecu reports actual speed assuming stock diameter tire. I've heard of lawsuit threats against lrna back in the day accusing them of getting out of warranties 10% quicker based on odometer readings. not sure how those ended, I think most had the service manager take on the work to keep it quiet

I've also heard of some 97 d90 owners getting busted on ecm mileage vs odometer mileage, but I don't know how true that is, gems would have to record mileage for that to work. Maybe someone with testbook experience can chime in on that one

 

[rover4x4]

how much variation is there between your coolant temp on the code reader and the gauge on the instrument cluster

 

[1MITCH1]

Temp gauge on dash has three readings.
Cold
Normal
You're fucked

 

[jafir]

Pretty much every car I've checked is this way. Currently I'm driving a 1998 honda civic until I get my LR3 back on the road, and it's off about 5-10% on both tach and speedo.

I do think my LR3 was pretty accurate though.