'95 S3 Tach problems and Pick-up coil.

I have a tach that is not working and I am in the process of trying to solve the problem. After reviewing the wiring diagram, it appears that the tach receives its signal from the pick-up coil. The pick-up coil being an electronic component that senses movement of the timing chain sprocket as it rotates. Is this correct ??? If this is true then I need to confirm that the pick-up coil is ok. Clymer's covers the procedure for testing the coil. Also, is there any relationship to the tach and the #3 coil as reported in previous posts on this site. Some members have reported dirty #3 coil connectors being the cause of tach problems as well.
Jim Morgan

Did you get it working jemllc? I have a similar dodgy tach and scraping the coil spade connectors doesn't seem to help (neither does cleaning the mysterious ic-board in the headlight wiring loom) (as suggested by trypcil).

Coincidently the ignition pick-up sensor failed a few weeks ago and having replaced it with a fresh one (thank you Sprint Manufacturing) I've only noticed the tach acting erratically since then but because my bike is running smoothly I figured that wasn't the cause of the tach problems.

What is it that drives the tach - a signal from the pick-up sensor? Something magical in the igniter box?

rik

[texspeed]

Do all your indicator lights work also? Especially the neutral light? Reason I ask is that recently I messed with the headlight shell (undid the mounting bolts and layed it on the fender) in order to mount some small horns behind it, under the top fork clamp. I've also in the past unbolted the headlight shell when mounting/taking off the bikini fairing I've got. Well, this last time messing with the headlight caused my tach to quit working. What drew my attention to this problem was when I went to start it I had no neautral light come on. I unbolted the headlight to start checking for any signs of loose wires with the bike running when I noticed that when I moved the headlight around the tach would intermittantly work, along with the neutral light. Ahh Haa!! Started messing with the harness between the headlight shell and the console/gauage cluster. That's where my problem lay. Looked in the manuals wiring section and found that the tach ground and neutral gauge light were grounded/ joined together............Buried midway in the main(large) harness between the gauges and the headlight is the two ground wires coming from the tach and neutral light crimped/soldered to a single wire that goes into the headlight. And it was broken (I slit the covering to reveal the wires) along with some corrosion. Broke from messing with the headlight to many times I figure. Recrimped and soldered, tied up the covering.............good as new. Good luck!

Not working yet. I have not had the time to perform the tests. From the Haynes WIRING DIAGRAM the pick-up coil goes directly to the igniter only. Tach has three wires leaving it, one goes to the igniter which appears to go be on the same node as two ignition coils (either 3 and 2 or 2 and 1) The other 2 tach leads are tied with the regular type electrical functions ( gages, lights, ect) and the other appears to be ground. Procedure to check the tach gage is to check continuity between the black/blue wire at the the tach. All that being said, I first plan is to check the tach. I recently replaced the #3 coil due to #3 cylinder not firing. The connectors looked good. So it is possible I just have a bad tach. The is rust on one screw on the face of the tach which is not a good sign. Keep me advised of your progress. Also, I suppose that the pickup coil tells the engine when to fire when it senses movement of the crank gears, similar to a distributor in an older model auto. So the I suppose the same signal is used for the tach, although not directly wired to the pick-up coil but vis the igniter. Another place to check would be the igniter connections.

Jim Morgan
jemllc

PS: Tex's post above is very good information.

[ This message was edited by: jemllc on 2004-05-20 06:50 ]

Thanks Jim & Tex,

I'll be sure to check the connections you advised and have a closer look inside the headlight wiring maze. Coincidently my right turn signal indicator light stopped functioning about the same time as the tach problems (all other lights, including neutral light work fine) but I just put it down to a blown bulb and never got round to replacing it. Well maybe the wiring is at fault - so you may have also saved me the price of a bulb!

Thanks for your feedback. I'll let you know my progress.

rik

[trypcil]

try switching the coils if you have'nt already!Could be a bad # 3 coil but if are'nt having a miss fire it may be the tach's gone south - there have been other cures listed on this forum! good luck! Share & Enjoy! :hammer:

Haynes in Chapter 9-17, 25.8 states that " Note the tachometer, oil pressure warning light, neutral light, side stand warning light and cooling warning light all share the same power supply from the fusebox, so if they are not working the fault must lie between the instrument wiring connector and the fuse box."

I have no indication of an neutral light or side stand light, never seen the low fuel, oil pressure or coolant light come on. When I turn the key on none of the five vertical bulbs light are on. Starting from the top, which light is which of the 5 vertical lights on the cluster ? There appears to be problem here.

Jim Morgan
jemllc

[texspeed]

From top to bottom: Coolant temp, fuel low, oil pressure, neutral, highbeam. There is no side stand indicator. Sounds like either a fuse, or more likely a bad connection, (open circuit.....the worst case)
An ohm meter is your best bet when checking for an open circuit going from component to connection, connection to connection, etc. Eliminate the obvious :fuses, bulbs..they do burn out often,and all visible connections.Fun part is figuring out where they connect up at in the hidden wiring maze!..... Good luck! You'll find it soon! :wink:

Thanks for all your help - I've corrected the problem with my tach and now frequently enjoy the site of the needle swooping up to 9000rpm (although there's not really much time to gaze at the rev counter at that acceleration).

Wiggling the socket on the back of the tach revealed a poor connection with the circuit board inside the tach. I contemplated opening it up (using the pictures in the photo album/shop scrapbook as a guide) but found that wedging a piece of cardboard to hold the socket firmly in place was sufficient to eliminate the intermittent open circuit which was causing the tach needle to be so erratic.

I hope the problem with Jim's tach is as simple to fix as mine - keep searching and you'll find the fault.

rik

[trypcil]

What does the mysterious IC board do , the one in the loom thats buried in the headlight - any ideas? Share & Enjoy! :razz: