Tach Dead 1991 ST1100

The other day tach stayed at zero. I gave it some throttle and it jumped and worked. A couple of days later dead again but this time it stayed dead. I checked all wires in back of tach and all connected OK including the bullet connector. Someone said there was something on the bike that sends impulses to tach from somewhere around the engine but I don't know what it is or where it is. Can someone help please? Thanks.

Replace your tach it is bad

If you have the Honda Service Manual, (maybe Clymer or Haynes have schematics as well), check the wiring schematic to trace where the wires go. Could be something loose elsewhere, although, I confess, I don't know where that "sensor" on the engine is either. Possibly it runs off a coil?

The Pulse Generator is located on the top rear edge of the engine case where it senses crankshaft movement. Pull the fuel tank and you'll see it easily. It sends its signal to the Ignition Control Module via yellow and white/yellow leads. The tach's lead from the ICM is yellow/green. I have pictures of the Pulse Generator on my desktop somewhere if needed. Years ago I had an oil weep at the generator and had to replace the gasket/seal. The Honda Service Manual has schematics of ignition system components' locations and flow diagrams (p. 18-2/3) and the Pulse Generator Inspection (p. 18-8) and Removal/Installation procedure (p. 18-9). HTH

John
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Cyclegeorge said:

The other day tach stayed at zero. I gave it some throttle and it jumped and worked. A couple of days later dead again but this time it stayed dead. I checked all wires in back of tach and all connected OK including the bullet connector. Someone said there was something on the bike that sends impulses to tach from somewhere around the engine but I don't know what it is or where it is. Can someone help please? Thanks.

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I have a 94 with a similar problem, try giving the Tach a couple of taps with the engine running to see if it is just stuck.Mine jumps to life when I tap it.
I hope all mine needs is to be cleaned and possibly oiled.

Slydynbye said:

I hope all mine needs is to be cleaned and possibly oiled.

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Possibly cleaned, but I highly doubt oil would be a good idea.

the old Shadows had a bad solder joint that was an easy repair ... ir you consider cutting apart the tach and resealing things back together "easy" ...
Anyhow, one of mine on the 91 STs died, and I had replaced the panel on the other, due to crash damage (the bike bought from Doghouse) so I had a spare and swapped them It was nice to just be able to plug in the cracked panel and test things to make sure before digging into the tupperware. Likely that is what you will need to do if you do not find any breaks or bad connections.

Cyclegeorge said:

The other day tach stayed at zero. I gave it some throttle, and it jumped and worked. A couple of days later, dead again, but this time it stayed dead. I checked all wires in back of tach, and all connected OK including the bullet connector. Someone said there was something on the bike that sends impulses to tach from somewhere around the engine, but I don't know what it is or where it is. Can someone help please? Thanks.

Click to expand...

The first thing to try, if possible, is to check the two screws into the white back of the instrument cluster that anchor the two electric wires for the tach. They take a #2 Phillips (or Jap equivalent) screwdriver and might be loose on a '91.

If your tach is still dead: I think the tach has simply one ground/earth wire (usually green) and one signal wire (with some yellow, I think). If you can, put a voltmeter across those two wires. That is, connect one meter lead to the ground wire (green), and one to the signal wire (yellow). Start the engine, and watch for a voltage change.

1. If a voltage change is seen, roll on the throttle, and look for even more voltage change. If seen again, tach is bad, or those wire connections have rust on them. (I'd double check for rust where the two wires bolt onto the back of the tach.)
2. If no voltage change is seen, you may have to pull your gas tank and go a looking at that pulse generator at the top rear of the engine. (But I've never seen one of those fail.)

Bottom line: I'd look for loose wiring or a rusty connection at the back of the tach. (That back of the tach can get wet. You have a rubber cover over it to shelter it, right? You get a lot of rain there in Plantation? Is that Florida? By the way, the instrument cluster is not that hard to remove and disassemble, IMO, if it comes to that.)

(Reference: Any ST1100 SERVICE MANUAL WIRING DIAGRAM.)