floating tachometer

[92Sierra]

Anyone else have their tach "float" back and forth occasionally by 300-500rpm? mine will read idle accurately but usually at cruising rpm it goes up by 300-500rpm more than it should and will go back to normal for a short time.
Just wondering if there is a fix for this or thread somewhere i missed?
thanks

 

[BLACK_1979_TA_SE]

How are your spark plug wires? Bad wires can cause erratic tach behavior...

 

[John Deere 4240]

I noticed that my ECSB 350 will do that sorta thing alittle but my CCLB dulley 454 does it alot. I've also noticed that the RPM jump only happens when I'm moving down a road, let off the gas, and the press on the gas again and it is revved up about 500 RPM for a few seconds and then goes back to normal. Sorta sounds like what you were saying.

 

[92Sierra]

How are your spark plug wires? Bad wires can cause erratic tach behavior...

The wires are in good shape from what I can tell. I plan on getting 8 or 8.5mm ones soon but the truck drives fine and doesn't act like there's any ignition issues.

 

[Horns]

I noticed that my ECSB 350 will do that sorta thing alittle but my CCLB dulley 454 does it alot. I've also noticed that the RPM jump only happens when I'm moving down a road, let off the gas, and the press on the gas again and it is revved up about 500 RPM for a few seconds and then goes back to normal. Sorta sounds like what you were saying.

That's your rpm's actually jumping in that case.

 

[dirtridinz71]

When the pickup coil in my distributor started going bad it caused the tack to jump up and down in rpm very errectically. It too did this just while cruising and at first would not feel the miss when driving the truck.

 

[Vortec Lover]

never heard of this problem... its usually the gas gauge

 

[Horns]

Every single one of my gauges jump around. Except the speedo.

 

[John Deere 4240]

That's your rpm's actually jumping in that case.

Oh lol misunderstood his comment the haha I didn't relive it was just his tach moving.

 

[BubbaZ71Tahoe]

sure its not the torque converter locking and unlocking? ... you will see rpm jump 3-400 if its doing that