Well guy's, wealth of knowledge on this board! I've searched and read and absorbed what I could.

03 Baja 275 performance with a 496-MAG.

Erratic and bouncing tach. RPM will go up and down during steady cruising or even at idle.

Bought new RAYLAR ceramic plug wires, replaced alternator all this past weekend without any remedy. Even pulled gauge cluster to check connections, plugged and unplugged everything. nothing has changed. (these are all the recommendations I've found on here)

I've thought about upgrading the gauges anyway, but would like to figure this out first. any chance it's the tach? Any suggestions on replacing the gauges does anyone offer plug and play?

Thanks for any help!

I'm having the same issue on a 502. Thanks for posting, will be curious to see what everyone says.

Iirc it's generally a ground issue, check and clean all the connections.

Had a cruiser doing that years ago.....bad ground on the tach.

does the tach ground go back to battery? (as it's the weather pack plug on the back)? or is it jumped in to another at some point?

I did check and clean battery connections, but I also installed new batteries last year as pm work and the tach never was affected. (didn't get better that is). it's been happening for a couple of years and has been getting worse.

is this a smartcraft Tach

Related problems - loose cannon plug in or wiring harness connection and or pin connection in the wiring harness cannon plug. Sometimes the pins need to be spread out for a better connection.

GROUND issue and or corrosion issue

Internal ground with the tach itself

Loose backside connection(s) to the tach

If old style analog tach - the pole setting on the back of the tach off its setting by a hair. Readjust. Again NON smartcraft gauge. Smartcraft gauge is both showing a analog reading and can show digital reading in that display.

I chased this issue for a couple of years on 500 efi's. I finally ran a wire right off a hold down screw on the distributor right to the block and the problem went away. I read somewhere that the paint under the distributor can effect its grounding. Not sure but it worked for me.

Don't think it's smart craft. it does have a 4 prong weather pack plug in the back of the tach. No terminals or posts.

No distributor either. It's the 496 mag. I did see that while searching. The distributor ground issue.

Been in contact with livorsi I'd be tempted to upgrade the gauges anyway. I'll pull the dash again this weekend and see if I find anything new. But what are all the grounds everyone is mentioning?

Have you removed and cleaned the ground from the battery to engine? possible corrosion within the cable itself.

All 496 / 8.1 have no distributors. This is PCM 555 controller in which is smartcraft compatible. If your gauge is just an analog gauge then its not a smartcraft gauge / and the rest gauge package. .

I will stick by what I posted earlier as you have analog gauges non smartcraft. Many 496's came with smartcraft gauges Just saying.