This is a discussion on 93 Chevy 1500 4.3 l within the Talk Car forums, part of the Tech Support Forum category. Truck runs good cold or about 5 plus Miles then starts to spitting back thru carb loses power give it
Truck runs good cold or about 5 plus Miles then starts to spitting back thru carb loses power give it gas runs better code 33 map sensor checking good with vom compression good vacuum good gas mileage terrible spark plugs changed but look good what else to check
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That is a TBI and not a CPI fuel system correct?
For the code 33 is the EGR valve vacuum hose connected to the MAP or does the MAP connect directly to the intake manifold?
At the MAP sensor using a T pin and a voltmeter and test light gently back probe the connector the purple wire should be a ground using a test light connected to battery positive key off and connector unplugged from the sensor the test light should light bright. Using the volt meter the gray wire is 5v reference and should read 5v with the sensor plugged in key on and the t pin back probed into the connector, the light green wire is the signal wire back probed it should read less then 1v with the key on and connector unplugged, plugged in it should read greater then 1v and less then 4v and change if you apply vacuum to the hose on the sensor(old school trick plug a new hose to the sensor and suck on it while watching the voltmeter)
This video is a little rough but gives the general idea>
Back probed the signal wire with a vom at the map and applied vacuum about 5 in hg at a time seems to be working properly. Haven't checked it with the engine hot as that seems to be when the problems occur thank you for the help
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