Wiring a tach (have I found a solution???)

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Mjollnir · #1 Post by **Mjollnir** » Tue Feb 24, 2004 11:31 pm

Alright guys, check this out. The holdup in wiring a tach seems to be that we have a positive discharge system. That means that there is no coil negative wire to hook up to. There are two wires. As best as we have figured, one is a contstant hot, and the other is the trigger wire. Check out this wiring diagram from Autometer, it is for the tach-adapter for a GM coil:

http://www.autometer.com/hp/instruction_do...uctions/561.pdf

Seems to me that this wiring diagram shows the same thing we have, only with 2 trigger wires, for whatever reason. The main point that I see, however, is that the adapter senses the ignition pulse over the positive wire and converts it into a 12v signal that is usable for a tach.

Check out the diagram and let me know if you think this would work. The other question, maybe for kdxboy or another resident EE, is if this device might put some sort of draw on the ECU that could fry it. I don't think it would, since it is installed on the 12V supply side.

All we need to figure out now is the answer to another question - does the plug fire every time the piston cycles, i.e. 2 times per "revolution", or just once? The Autometer cycle tachs can be set up for 1 pulse or 2 per revolution - I assume this is what it is talking about, right?

What do you think? I'm excited, as I think this might work.... Who wants to be the test dummy? If someone has a spare ECU I can use, I will try it.

Marc

bouncerdude · #2 Post by **bouncerdude** » Wed Feb 25, 2004 3:54 am

the diagram for the tach didnt load up for me, but ill try and take a stab at it. the gm tach diagram would show it having to trigger wires because if its going to a triggering coil it needs a positive and a ground. it shouldnt draw that much current becuase its just an analog meter. i would guess that the plug fires when the piston makes one complete revolution. i may be wrong but im just taking a guess. im positive that there is atleast one person on this site who knows the answers to you questions, and others too. for example: "Where to babies come from?" lol.

TheJaspMan · #3 Post by **TheJaspMan** » Wed Feb 25, 2004 2:20 pm

Two-stroke engines fire once every revolution, while four-stroke engines fire once every other revolution.

Mjollnir · #4 Post by **Mjollnir** » Wed Feb 25, 2004 4:23 pm

Bouncerdude - I'm pretty sure I know where babies come from. My third is on the way. I think I've finally figured out how this keeps happening, and have made appropriate arrangements to prevent it from happening again.

JaspMan - You are absolutely correct from one perspective. A 2 stroke FIRES every revolution, and a 4 stroke fires every other revolution, but there has been some discussion regarding whether the spark plug on the dale fires at the top of the exhaust stroke as well. Apparantly that is pretty common on single cylinder engines. It doesn't serve a purpose, it's just a matter of simplicity due to the trigger mechanism. However, the tach would need to be calibrated to read it correctly - if it was only looking for 1 spark when there is actually 2 for every 1 that it's looking for, it would read double, i.e. 10000 rpm when you're only turning 5000.

See what I mean?

Marc

TheJaspMan · #5 Post by **TheJaspMan** » Wed Feb 25, 2004 4:30 pm

QUOTE

Originally posted by Mjollnir
Bouncerdude - I'm pretty sure I know where babies come from. My third is on the way. I think I've finally figured out how this keeps happening, and have made appropriate arrangements to prevent it from happening again.

JaspMan - You are absolutely correct from one perspective. A 2 stroke FIRES every revolution, and a 4 stroke fires every other revolution, but there has been some discussion regarding whether the spark plug on the dale fires at the top of the exhaust stroke as well. Apparantly that is pretty common on single cylinder engines. It doesn't serve a purpose, it's just a matter of simplicity due to the trigger mechanism. However, the tach would need to be calibrated to read it correctly - if it was only looking for 1 spark when there is actually 2 for every 1 that it's looking for, it would read double, i.e. 10000 rpm when you're only turning 5000.

See what I mean?

Marc

I think so. If I understand it correctly you fired your mailman? lol

So is it possible it also fires on the exhaust stroke? That would offer one reason why plugs foul so easy when not run for very long. The cold engine is not igniting all the fuel, and when the exhaust stroke happens the plug doesn't fire hot enough to burn it all off without back firing. Right?

Mjollnir · #6 Post by **Mjollnir** » Wed Feb 25, 2004 5:05 pm

Bouncerdude - I'm pretty sure I know where babies come from. My third is on the way. I think I've finally figured out how this keeps happening, and have made appropriate arrangements to prevent it from happening again.

JaspMan - You are absolutely correct from one perspective. A 2 stroke FIRES every revolution, and a 4 stroke fires every other revolution, but there has been some discussion regarding whether the spark plug on the dale fires at the top of the exhaust stroke as well. Apparantly that is pretty common on single cylinder engines. It doesn't serve a purpose, it's just a matter of simplicity due to the trigger mechanism. However, the tach would need to be calibrated to read it correctly - if it was only looking for 1 spark when there is actually 2 for every 1 that it's looking for, it would read double, i.e. 10000 rpm when you're only turning 5000.

See what I mean?

Marc

thunderwolf · #7 Post by **thunderwolf** » Wed Mar 10, 2004 11:06 pm

Trailtech is coming out with a new computer that will have a tach and a temp gauge built in. Maybe if we get enough people to e-mail them they would make one for our cannondales. They talk about the new features here .

thunderwolf · #8 Post by **thunderwolf** » Wed Mar 10, 2004 11:22 pm

Here is an excerpt that I stole from another site that was written by Trailtech.

"The new tach will bolt to our existing bar mounts but our curent aluminum surrond will not fit. The new tach/speed/temp gage is the same size as our current aluminum guard. target release is early summer. target price is $99. You can see the basic shape on our web site at:

http://www.trailtech.net/trx450.htm

click on the picture to make it bigger.

The LED's in the bezel are shift lights (two programmable shift points).

The LCD has a RPM bar graph (4" wide). It also has speed/distance/time/temperature capabilities. It will only accept one temperature input (oil, water or EGT). For the LED's to work, the unit requires power from the quad. It also a remote switch."