Tachometer Testing

[twigg]

After a series of ignition issues I have most of them resolved.

 

New plugs, plug caps and wires have made all the difference.

 

I also removed and split the TCI. The diodes are in perfect condition so I left them alone. I re-flowed the solder in the pin headers and put it back together. The bike fires up, runs just fine right up to the red line.

 

Before I did this I was having an issue of cylinder #2 not firing, and the tach behaving a little strangely. Cylinder #2 would quit, and the tach with it (sometimes).

 

Now it's all back together the four cylinders are all playing nicely but the tachometer is dead.

 

This may simply be a dead tachometer. What I was wondering is whether or not there is any way of testing the ouput on the grey wire from the TCI (tach signal).

 

Is there anywhere else I should be looking too?

 

Thanks

[dingy]

The grey wire is tied directly to the grey wire that triggers #2 cylinder coil. This connection is in wiring warness.

 

With the key on, all the coils receive a 12vdc signal from the TCI, this signal is interuped at the instant the coil is to fire, as signaled by TCI. FYI, this is the opposite of the way a CDI works, the coils are normally 0VDC, and when signaled to fire they receive a 12vdc pulse from CDI.

 

With the 12VDC signal on the coil normally, the grey wire in the instrument head could be probed to see if it has this 12vdc on it. If it does, then that wire & connection is good.

 

Gary

[twigg]

Thanks Gary ... I will go check as it's all in bits right now so it's easy.

[MiCarl]

The TCI grounds the coil via the gray wire. Hot is provided by the red/white wire to the coils. Most of the time the engine is operating the gray wire should read 0 volts to ground.

 

I believe the the TCI will drop the ground if the engine is not turning, resulting in the gray wire reading (+) 12V. I don't know if that's instant or if there is some kind of time delay.

 

I'd be inclined to use a test light with its (+) connected to the battery and probe the gray wire with the light (-) and the engine running. If you have continuity back to the TCI and power to the tach your light should flash.

[twigg]

Withe the engine OFF and the ignition ON, the pin leaving the TCI is showing battery voltage. Same voltage is indicating where the Grey wire connects to the back of the Tach.

 

Yes, I would think that a test light would "flicker" as that contact switches to ground once per revolution.

 

It's beginning to look like the tach itself is the problem.

[dingy]

The TCI grounds the coil via the gray wire. Hot is provided by the red/white wire to the coils. Most of the time the engine is operating the gray wire should read 0 volts to ground.

 

I believe the the TCI will drop the ground if the engine is not turning, resulting in the gray wire reading (+) 12V. I don't know if that's instant or if there is some kind of time delay.

 

I'd be inclined to use a test light with its (+) connected to the battery and probe the gray wire with the light (-) and the engine running. If you have continuity back to the TCI and power to the tach your light should flash.

 

 

I got to quit posting at work, no reference material to check.

Carl is correct, 12vdc- is side that is interupted, not 12vdc+ as I said earlier.

So put positve side of voltmeter on positve terminal of battery and with negative terminal read grey wire.

Gary

[twigg]

I got to quit posting at work, no reference material to check.

 

Carl is correct, 12vdc- is side that is interupted, not 12vdc+ as I said earlier.

 

So put positve side of voltmeter on positve terminal of battery and with negative terminal read grey wire.

 

Gary

 

I got that Gary, thanks.

 

Here is what I think you guys are saying ....

 

Ignition ON, engine not running ... Grey should read battery voltage.

 

Engine Running the grey is interrupted to ground once per rev (When cyl #2 fires). In this case, a test light between Grey wire and battery +ve should flash when the wire goes to ground.

 

Right?

[bkuhr]

Dont forget to check for batt and ground on the other tach wires.

Also may help to loosen then retighten tach wire nuts, just to rule out corroded connection.

 

I had simular issue- sometimes tach worked, sometimes only fraction actual rpm. I took tach apart and lubed thinking corroded mechanics. I ended up making it not work at all:doh:. Finally replaced it.

[dingy]

I got that Gary, thanks.

 

Here is what I think you guys are saying ....

 

Ignition ON, engine not running ... Grey should read battery voltage.

 

Engine Running the grey is interrupted to ground once per rev (When cyl #2 fires). In this case, a test light between Grey wire and battery +ve should flash when the wire goes to ground.

 

Right?

 

Again, I am at work trying to wing this.

The grey would not be interupted to ground, it should be grounded when key is on and engine not running.

The TCI should make this circuit go open when the coil is signaled to fire. This causes the coil to become de-energised and the field collapses, thus inducing voltage into the secondary of the coil, causing the secondary to build a high potential difference voltage across the spark plug, which then arcs.

The grey wire should read 12vdc when read to the positive terminal of battery at key on - bike not running.

It will go open every other revolution on 83-89 bikes with stock TCI. On 90-93 bikes this occurs every revolution with a stock TCI. The ignitech unit also does same every revolution on 83-93 bikes. This is not like a set of points on a car, it is triggered by the stator magnets moving by the pickup coils with sufficient speed to induce a current in pickup coils to trigger TCI. In other words, you will not see the grey wire go open if you slowly rotate crank shaft.

Only do checks on this with a digital meter. Analog meters are not good to use on circuits that have electronics components in them.

Gary

[twigg]

Okay ... Tach is now working

 

After poking around the back, checking voltages, and the old "bang the TV on the top to fix it" technique, it sprang into life.

 

That tells me that something is loose (or sticking). I shall pull it to check.

 

For the record, with a working Tach:

 

Black Wire: Continuity to ground

 

Brown Wire: 12V (Engine OFF, Ignition ON

 

Grey Wire: 12V (Engine OFF, Ignition ON)

 

If I get to drop by Autozone I'll pick up a lamp flash tester and check that Grey Wire with the engine running.

 

Thanks for the help guys