Tacho accuracy

[Guest]

I suspect that on occasions either my tacho or speedo is inaccurate.

When travelling 80 km/h, the motor is usually turning over at a steady 1875 rpm. However on occasion it sits at around 2100 rpm. Conditions are the same, driving on straight road, no extra weight in the car, no aircon etc. No difference in engine noise as far as i can tell.

Not sure if anyone has experienced this also, or maybe it's just me being paranoid.

 

[Scottie]

You sure it isn't the torque converter not locking up? Would make about that many revs in difference.

 

[bradc]

you'll have an auto, and when the car is cold they do that for up to 10 minutes. To confirm it, chuck the car down into 3rd or 4th on the same road at the same speed, and you will see that in the lower gears it is always the same rpm.

It is only when you're pootling around in 5th at low revs that it does it. Which by the way you shouldn't be doing, if you drive regularly in 5th gear below 70kmh you'll chew the torque converter to pieces and need to buy a new gearbox. Keep it in Tip and select the gears properly

 

[Guest]

I'll have a go at 3rd and 4th gear rpm readings tonight. Can't remember if it only happened in the first 10 minutes of driving or not, but i was going 80km/h in 5th.

I also didn't realise about the torque converter. Transmission puts it into 5th if i'm cruising at 60 so i just leave it, i figure the computer would know best.

 

[bradc]

I found that at 110kmh in 5th it would sit at 2700rpm for some time before dropping down to 2500rpm.

The ecu is pretty good at gear selection, but it does select 5th way too early for it's own good

 

[Guest]

So basically there's nothing that can be done. it's just something the ECU does in the first 10 min or so of driving.

But to ensure the torque converter's life, don't drive in 5th at low rpm.