Hey Everyone,

I posted earlier on speedometer and tachometer-(RPM cluster) question. I found and fixed the issue on the speedometer. Need to dry and re-tape the VSS unit on the rear differential. Tachometer is going a little weird. I had some of you telling me that the tachometer might need to be changed.

I just wanted to give you another issue on the tachometer and to get some feed back. It might be that I have to change the tachometer, but here is the other issue I'm having. Sorry it's long.

The tachometer and speedometer had been reset by turning off the truck. I double checked by turning on an off the truck and hitting the reset button on the dash an waited to here it reset.

I was driving around for a few day an everything was working fine. I wanted to check my ESOF system, hubs and vaccum lines. I was driving today on 4x4 high and my tachometer started to decline to zero. When I switch back too 2H the tachometer went back up to normal. Just to make sure I switch back to 4H and it happen again. Is this due to the vaccum lines, PHV solenoid, fuses, relays or electic motor next to transfer case going bad? Or is it the tachometer needs to be changed?

Also while driving around 50 miles my floor heat turn to defrost. When this happen the tachometer also went down to zero. I know the sign from floor heat to defrost is a vaccum leak, but does this also affect the tachometer RMP. I will also check and change all my lines. It might be a small hole or crack somewhere in the lines or connection. Again, sorry it's long I just wanted to give you all the information.

Thanks,

 

The tach should be ECM controlled and use the CPS for engine position and rotation reference. It sounds almost like the 4x4 light causing a ground issue for the tach. If you want to try some diagnostics, try removing the 4x4 bulb or 4x4 switch and see if the problem comes back. With the bulb out, try engaging 4wd.

 

ReAX - That so weird, because when I turn on my lights I have to tap my 4x4 switch on my dash a few times to light up. Or when I switch from 2h to 4Hi it will turn on. Do you think I need a new switch?

Also today while driving on the freeway in normal 2h my tachometer needle drop down again. I hit the gas too pickup some speed and I noticed the needle dropping. I didn't feel like I lost power just that the needle went down to zero and it had a hard time going back up.

Do you think its still the 4x4 switch or my tachometer? Again, its weird that you mention the light issue on my 4x4 switch.

Thanks

 

doing your own diagnostics is usually free (unless you screw up it is.) I would say try unplugging the 4wd switch and driving a couple of days. If the problem doesn't return, you have the culprit.