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Ignition ECU to Fuel Injection ECU - negative voltage? 200 1988

posted by  tbb2 on  Sun Apr 3 12:22 CST 2011
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last visit: Wed Jul 16 18:57 CST 2014
[RELATED]

I am inspecting Fuel Injection and Ignition systems.

While doing the Green Book tests on the Fuel Injection ECU harness connector I got an odd voltage reading?

-Check engine speed signal
--pin #1 to ground
** --Ignition Off - minus 0.3 mV (spec is 0.0 V)
--Ignition On - 12.24 V (spec battery voltage)
--Starter On - 7.8 V (spec at least 1/2 battery voltage)

This is the off reading.
** --Ignition Off - minus 0.3 mV (spec is 0.0 V)
Looking at wiring diagrams, this is a small trickle of current between the Ignition ECU to Fuel Injection ECU.

The ignition switch is off so there is no power going to Ignition ECU.

Other that the rotting wire theory, that I would strike me as odd since I have gotten the exact same reading twice on different days ... then electricity is not my strong point ...
any suggestion on the source of this trickle?

Also - what is the source of the engine speed signal?







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