Shane661
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posted May 20, 2009 01:48 PM
 Edited By: Shane661 on 20 May 2009 22:35
Stewart Warner Car Tach??
I came across a good deal (?) 11k rpm SW tachometer. I am using an inline tach signal adapter, coming off of one coil connection. It works fine with my MSD shift light, but not with this tach.
I installed an inline resistor to calm any noise down, but it still does not work right. It will read somewhat normal (at idle) if set to 2 PPR. If set to 1 PPR the idle is double the actual. As soon as I rev the engine, the tach goes crazy. I have run the ground straight to the battery, still no luck.
Any ideas? This unit was purchased as "new" off of Ebay, but it could be defective. Anyone else using/used a car tach? If I can't get this one to work, I'd like to find one with a 5" face that will.
Shane
  
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Shane661
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posted May 21, 2009 05:14 AM
Bump...
I am pretty confused on this one...I figured it would run off of 1 pulse per revolution, not two??
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Shane661
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posted May 21, 2009 09:38 AM
Nice to know that I'm not the only person who is clueless about these things...
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tcchin
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posted May 21, 2009 04:49 PM
There are two things that I can think of, other than a broken tach and complete electrical system incompatibility, that would make a tach behave like that: 1) Lack of vibration isolation; 2) Non-resistor plugs or other sources of RFI.
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dougmeyer
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posted May 22, 2009 11:22 AM
Is it a tach that is listed as appropriate for a CDI Ign?
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Shane661
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posted May 22, 2009 11:45 AM
Edited By: Shane661 on 22 May 2009 19:56
quote:
Is it a tach that is listed as appropriate for a CDI Ign?
Doug, I am pretty dumb about these things. Here is a link to the instructions:
http://static.summitracing.com/global/images/instructions/sww-114012.pdf
It says, "NEVER CONNECT GREEN WIRE TO THE COIL WHEN USING AN MSD OR SIMILAR HIGH
OUTPUT CAPACITIVE DISCHARGE STYLE IGNITION SYSTEM
Damage to the tachometer will occur—Connect GREEN wire to the tachometer terminal only."
Is the bike setup a "high output CDI style ignition" like the MSD?
If that is the case, where would I pick up the signal on the bike; would an injector wire work? I am fairly confused about this.
Shane
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dougmeyer
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posted May 22, 2009 04:43 PM
Based on those instructions, I would try and isolate the tach signal wire from the ecu and put the green wire there. Skip the coil. I don't have a schematic handy, I seem to have misplaced my manual, so I can't tell you which wire that is- but someone can.
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Shane661
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posted May 22, 2009 05:03 PM
There doesn't seem to be a tach signal wire on the 14. I think they may be using multiplexed signals...
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entropy
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posted May 22, 2009 06:06 PM
i log rpm using an injector signal; maybe that would work?
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whitehendrix
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posted May 22, 2009 08:32 PM
hmm... an inline resistor won't calm noise down at all.. a small-value L-C circuit might make an effective choke and EMI/RFI suppressor.
i'd test the thing first on something simple.. a car.. a lawnmower. .anything that'll prove that shit works at all.
i'm thinkin maybe you're seeing CEMF generated by the coils flux collapse.
a diode might remedy that.
in case i sound like tim, layman's terms- the CEMF is a backvoltage (counter ElectroMotiveForce) thats generated when the magnetic field collapses and induces the power to create the spark on the secondary side.. well, that works both ways. a backvoltage is also generated on the primary.. theres a slight chance you're seeing that feedback. i can't promise you i'm right, but it's just my sad .002 for what it's worth.
thats why you'll often see a diode in parallel with the coil of a relay. it takes that spike and absorbs it basically.
the only other thing i can thik of is to do what master Karl said and run it off the injector signal.. not sure if a power commander will affect the reading tho.
damn.. had another idea but it won't i don't think. i was gonna say tie into the trigger coil loop, but i dunno the voltage, and as well, theres mroe ppr than what the tach can use. it would probably end up reading 8Krpm or something goofy at idle..lol
Hmmm.. wierd stuff. can you maybe convert to an inductive pickup? kinda like how a timing light works..
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Shane661
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posted May 23, 2009 04:44 AM
I believe that one of the power commander wires is also rpm; I wonder if that might work?
I have an inductive that came with my MSD shift light...but it reads too low (but smoothly). No matter what I set the PPR on the tach to, the pickup reads way low and won't read higher than 3k rpm.
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whitehendrix
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posted May 23, 2009 09:57 PM
ya.. theres a rpm feel to the PC but i'm not sure which one it is..lol
that might work.
thats weird man.. i'd personally be breakin out the oscilloscope and tracing shit out, but thats just me..lol
i dunno what to tell ya bro.. other than goin back to what i suggested maybe and as well, seeing if that bad boy works in the first place.
____________
Duct tape is the handyman's secret
weapon. The black is for formal
occasions. - ZRXDean
ill never own a busa unless
someone gives me one.... and then
ill sell it -KZScott
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