Hi. If I follow my service manual, while the ignition is on and the connector is unplugged from the Map, I should have 5 volts at the red wire while grounded to the battery, 5 volts when I stay on the red and ground to the green wire, and while continuing to ground on the green, touch positive to the white wire and I should also get 5 volts. I do not have 5 volts at the connector when I put positive to the white wire. I have 4 volts. According to the service manual, I am suppose to replace the ECU. If I plug the connector to the MAP while the ignition is on, I get 5 volts on the red, 5 volts on the red and green and 2.90 volts on the white and green (negative). The map holds vacuum, and the voltage decreases as I apply vacuum. Is the service manual correct? Do I have a problem with the ECU or the MAP if the voltage at the unplugged connector is 4 volts on the white wire and 2,90 volts when plugged in to the map. I am unclear if this service manual is even correct. I there someone out there that has specific knowledge on 88-91 civic map sensor testing. My manual always uses the ECU as a scapegoat and suggests replacement every time for every sensor. Thanks, Richard

 

A couple of things:

- The service manual flow chart is for diagnosing a code 3, not really for preventative 'is my MAP sensor going bad' testing.
- The service manual asks for "approximately 5v".

Also, did you try measuring the voltage across the ECU terminals, you don't need the jumper harness they stipulate, usually you can get continuity with just prodding the probes into the back of the connectors.