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Originally Posted by BLACK94TT
Clint,
I just realized that my electronic Autometer boost gauge utilizes the GM map sensor. Can I tap its signal wire and take it to A22-green/black? And do the same with its ground, going to A22-black?
Not knowing enough about electronics, will tapping the already in use sensor degrade the signal causing erroneous readings at both the gauge and logger?
Looks like I'm over here now.  |
Short answer - Only connect the signal line, not the ground line. More details below.
SIGNAL LINE
Output impedance of the GM map sensor is quite low and the input impedance on the ECU is relatively high so it should not load the MAP output. (Autometer gage input should also be a relatively high input impedance.)
GROUND LINE
This one is a bit more complicated. Depends on what "Ground" you used for your autometer install. If you used "Signal Ground" of the ECU you are all set and there is no need to connect the ground lines.
And if you used a different "Gound", you still don't want to connect the ground wire because this can form a "ground loop" where current is flowing in the ground lines.
Quick DC measurement between Ground of the MAP sensor and Sensor Ground of the ECU A22-black will tell you how much error you would have. (ECU input has 8 bits of resolution so a .020 volt error will produce a 1 bit or ~.2 PSI error.)
SIMPLER EXPLANATION (No DVM required)
Start car and observe Autometer pressure at idle. Connect signal wire of MAP sensor to EGRT input.
1. Note whether there was any change in Autometer gage reading
2. Compare pressure of Automater gage and the display on the logger. If they are within +/- .2 PSI you are good to go.
NOTE - I will add a note at the beginning of this post to highlight the fact that if you already have an AutoMater Boost Gage, you can have boost logging for the cost of about 36" of 18 gage wire and a couple crimp on connectors! PICS of your AutoMeter install would be appreciated.