I am working on a john deere 5210 currently that we use for spraying. I had to replace the gauge cluster on the tractor because the fuel gauge failed on it. After replacing we used it for a season and it seemed that the rpms off. So we got a non contact laser tachometer to test if it was off. I tested the the rpms with the non contact laser tachometer off the crankshaft pulley and the results showed that the tachometer is not reading correctly but everything else on the cluster is working correctly. My question is there a way to adjust to correct it or could it be a faulty cluster that I got? Also could it be something else wrong with the tractor.
The result I got from testing:
Gauge RPM: Actual RPM with non contact laser tachometer:
1500 18701700 2120
I would first check and see if you have the tach switch in the correct position. On the back of the dash cluster there is a small switch that needs to be up for the three cylinder engines. If this does not fix the problem then I would check the wiring going to the engine speed sensor. It is on the left front top side of the timing gear cover. If the wiring looks good then replace the speed sensor. I would bet you have the switch in the wrong position.
More than likely the one you are using is setup for 4 cylinder and not 3 cylinder. If is an old one there will be a switch on the back. If it is a new one it has to be programmed for 3 cylinder. There is a kit to do this, but I believe it is around $75. I would call your local JD dealer and see, if they will program it for you.