Hello everyone,

I recently ran into an issue where the car wouldn't start unless I set my injector flow rate to 22lb when my injectors are 27lb. After it was running I would have to set the flow rate to 26 to keep it running.

Only code was map high 33 while performing this process. After about 5 minutes of running nearly every code triggered and I would have to do the above procedure to get her started again.

Tested the map sensor voltages and all was good. 5v on one and .8 on the other with a good ground on the black. Used a standard multimeter and a hat pin to probe through the wires insulation. This test is done with the ignition on and the car not running.

To do this test
1) Put the black lead of the multimeter to the battery ground and keep it there for the remainder of the testing
2) push a steel hat pin through the insulation on the black MAP sensor wire and touch the red lead of the multimeter to it and test for resistance -should be 0 ohms
3) Remove the hat pin from black MAP sensor wire and push it into the grey MAP sensor wire
4) Turn the ignition on but do not start the car
5) Set the multimeter to DC volts and touch the red lead of the multimeter to the hat pin -should read 5 volts
6) Remove the hat pin from the grey MAP sensor wire and insert it into the light green wire
7) Touch the red lead from the multimeter to the hat pin -should read less than 1 volt mine read .8 volts
8) Ignition off, hatpin removed, multimeter removed, test complete

more info: http://www.chevythunder.com/map_code_33.htm



I put a vacuum gauge in line with the sensor to verify I was getting pressure change and that the vacuum line wasn't broken or clogged. I had to have the car running for this test

Replaced the sensor and all is good.

Figured I would share my experience since I didnt find much out there about this troubleshooting process