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Indy
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Last seen: 2 years 1 month ago
Joined: 03/24/2015 - 07:49
Erratic RPM Log

My RPM is varying between 900 and 29,000 which is greatly out of range on the top end. I didn't rev the motor over 3500 RPM. I tried logging at 20/sec and 10/sec, but as expected that did not make a difference. The RPM graph does shift up and down depending on the throttle position.

I disconnected the one new device(SpeedHut Tach) that also connects to the (-) side of the MSD Blaster coil. That made no difference

I have a different configuration this time than I did last summer when it worked as expected on the same car. I have rewired the complete car, so that is different.

Any ideas as to what is causing the erratic RPM graph? What can I do to fix the problem?

 

Indy
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Last seen: 2 years 1 month ago
Joined: 03/24/2015 - 07:49
Never mind I figured it out.

Never mind I figured it out. The MSD distributor has a dedicated wire just for tach output.

 

AEM_NS
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Last seen: 1 year 3 months ago
Joined: 06/06/2014 - 09:31
Yup, you got it.  Definitely

Yup, you got it.  Definitely don't want to connect the coil primary to the AQ-1 for a tach signal.  Use a dedicated tach signal output like you found because it outputs a clean square wave that the AQ-1 can receive and register.  

AEM_NS
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Last seen: 1 year 3 months ago
Joined: 06/06/2014 - 09:31
BTW, connecting the coil

BTW, connecting the coil primary as the tach signal to a digital input on the AQ-1 exposes the logger hardware to very large voltage spikes (hundreds of volts) which can damage the unit.  Please be aware that the instuctions state that the digital inputs should be limited to 16.5v.  Would hate to see that you damaged your AQ-1 by making a bad connection. 

Indy
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Last seen: 2 years 1 month ago
Joined: 03/24/2015 - 07:49
Thanks again for the help!

Thanks for the followup info!