Tachometer flaking out

[Sporadic]

Just traded up to an 08 Mastiff and my tach ring started flaking out on me in the first 100 miles. Was fine when I left the shop. Left the house and when I started it the tach LED's didn't light. About 10 miles down the road they started working again. Stopped at a watering hole and the same thing happened when I left, but took about 15mi to light up this time. Any ideas as to what's going on here? I called the dealer, but only talked to a sales guy. He said it could just be the sensor needing cleaning from sitting so long and if it doesn't clear up to bring it in... I'm not positive on how the tach gets its data, but thought it was from the crank sensor (first bike w/ sensor or tach). Speedometer, odometer, and other indicators work fine. And if that's the case wouldn't I have ignition issues?!?! Can someone clear me up here or point me in the right direction before I call BS on him? Anything I should check first? Thanks!

 

[MARV]

tach gets input from the ign module.

you have a crank sensor not cam.

speed sensor is in the trans

 

[Sporadic]

tach gets input from the ign module.

you have a crank sensor not cam.

speed sensor is in the trans

Not enough coffee yet, crank is what i meant But doesn't it go crank sensor->ignition module->tach? If so and the bike is running that tells me it's not sensor related. Thanks!

 

[Cutter]

Have them clean the sensor, but it might be a weak battery as well...

Mine was strong enough to start the bike as long as it wasn't below 40, but a new bat cleared up the speedo, tach and odometer problems... make sure you are getting the full 12.8.

The electronics are crazy sensitive.

 

[chacha]

smells like a grounding problem to me. I think the 08 tach line doesn't even pass though the EHC, so you should be good there

 

[Gas Man]

Its not going to be the crank sensor if the bike is running... the crank sensor runs the ignition. The tach just comes off the ignition... its a single wire pick up from the ignition for data.

 

[Sporadic]

Thanks for the input everyone. Just to follow up on this, had the issue checked out by the dealer last week. Mechanic said the tach line from the ignition does run through the EHC (rev hit recording). They pulled the tach ring and went through all the wiring and the issue seems to be centered around the EHC. He bypassed the EHC and when the tach is connected directly to the ignition, it works fine. He also said the EHC wasn't recording rev hits when the problem was occuring. New EHC is on order and I take it back in next week. Will follow up once the issue is solved. Thanks!