BMW Intermittent Tach

STUFF2C · 12-31-2004, 12:14 PM

I need some help with my tachometer. I have an 87 BMW R80 with an electronic tach. It just recently started to Bounce/Wave after I ride for a while 83k miles. It is an intermittent problem. This is the dumb part. Any suggestions?

Possu · 12-31-2004, 01:53 PM

Charging problem?

Rubber Cow · 12-31-2004, 02:21 PM

Check the battery connections and all of the ground wires for corrosion. Better yet, remove them all includignt he battery cables, clean thoer contact faces with 600 grip wet/dry sand paper and re-fasten them with dielectric grease (found at most hardware stores). Do the same with your fuses, the few that there are. These models of tach are very sensitive to poor grounding.
Hope this helps.
Cheers,
Jorge

dehager · 12-31-2004, 05:05 PM

Quote:

Originally Posted by STUFF2C

I need some help with my tachometer. I have an 87 BMW R80 with an electronic tach. It just recently started to Bounce/Wave after I ride for a while 83k miles. It is an intermittent problem. This is the dumb part. Any suggestions?

I don't have a schematic in front of me but it could mean you have a hall sensor about ready to fail. On oilheads the same wire from the motronic goes to the tach and the coil. Any starting problems or missing while driving? It would feel like you hit the kill switch for a few seconds.

Some Hall Sensor info here, it's for oilheads but it should help.
http://users.rcn.com/dehager/

Google ??? BMW Hall Sensors, there is a site that talks about airheads.

johnjen · 12-31-2004, 06:40 PM

Also check your coil (both primary and secondary), and spark plug wires for opens. Sometimes the tach will begin to fail in just this way as well (you're at about the mileage where they can begin to wear out), in which case replacement/repair is necessary. This also applies to the speedo.

JJ

Frank Warner · 01-03-2005, 03:45 PM

On some of the airheads the ground for teh tacho was through the handle bars - and thus through the steering head bearings. Not a good idea. Suggest you run a new ground wire from the tacho back to the main ground point - On my G/S that is under the fuel tank on the main frame. Not the battery ...

If your hall effect sensors were failing you'd feel the power loss. Sp I don't think that is your problem.

STUFF2C · 01-03-2005, 06:06 PM

I spent my new years with a wire brush and grease, with all the suggestions I'm sure I'm headed in the right direction.
THANKS!

12-31-2004, 12:14 PM	#1
STUFF2C ^OP We Ain't Left Yet!! Joined: Aug 2004 Location: O-lando Oddometer: 1,176	BMW Intermittent Tach I need some help with my tachometer. I have an 87 BMW R80 with an electronic tach. It just recently started to Bounce/Wave after I ride for a while 83k miles. It is an intermittent problem. This is the dumb part. Any suggestions? __________________ Thanks to the Interstate Highway System, it is now possible to travel from coast to coast without seeing anything. -- Charles Kuralt I never plan a ride, just the destination and that's always subject to change.

12-31-2004, 01:53 PM	#2
Possu de-nOObed! Joined: Jan 2004 Location: Oxford, UK Oddometer: 5,050	Charging problem? __________________ www.possu.smugmug.com

12-31-2004, 02:21 PM	#3
Rubber Cow GS Dork Joined: Jul 2001 Location: Aloha... yes, Aloha, Oregon Oddometer: 5,299	Check the battery connections and all of the ground wires for corrosion. Better yet, remove them all includignt he battery cables, clean thoer contact faces with 600 grip wet/dry sand paper and re-fasten them with dielectric grease (found at most hardware stores). Do the same with your fuses, the few that there are. These models of tach are very sensitive to poor grounding. Hope this helps. Cheers, Jorge __________________ "He had that rare weird electricity about him--that extremely wild and heavy presence that you only see in a person who has abandoned all hope of ever behaving"normally"." HST-RIP "Woof, woof woof woof ...woof woof!!!!!!!!!" Cricket the Dog-RIP

12-31-2004, 06:40 PM	#5
johnjen Mod-U-Later Joined: Nov 2001 Location: Seattle Oddometer: 13,506	Also check your coil (both primary and secondary), and spark plug wires for opens. Sometimes the tach will begin to fail in just this way as well (you're at about the mileage where they can begin to wear out), in which case replacement/repair is necessary. This also applies to the speedo. JJ __________________ QUOTE from vermin I lie to myself because I am the only one who continues to believe me.

01-03-2005, 03:45 PM	#6
Frank Warner Traveller Joined: Mar 2002 Location: Sydney, Australia Oddometer: 6,593	On some of the airheads the ground for teh tacho was through the handle bars - and thus through the steering head bearings. Not a good idea. Suggest you run a new ground wire from the tacho back to the main ground point - On my G/S that is under the fuel tank on the main frame. Not the battery ... If your hall effect sensors were failing you'd feel the power loss. Sp I don't think that is your problem. __________________ Regards Frank Warner motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S http://www.geocities.com/fwarner_au/

01-03-2005, 06:06 PM	#7
STUFF2C ^OP We Ain't Left Yet!! Joined: Aug 2004 Location: O-lando Oddometer: 1,176	thanks for the input! I spent my new years with a wire brush and grease, with all the suggestions I'm sure I'm headed in the right direction. THANKS! __________________ Thanks to the Interstate Highway System, it is now possible to travel from coast to coast without seeing anything. -- Charles Kuralt I never plan a ride, just the destination and that's always subject to change.

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