# 93 Chevy 1500 4.3 l



## Robot135 (Dec 22, 2018)

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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## Corday (Mar 3, 2010)

Check fuel pressure.


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## Robot135 (Dec 22, 2018)

Fuel pressure is good 12 psi and steady


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## Wrench97 (May 10, 2008)

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>


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## Robot135 (Dec 22, 2018)

Map hooks directly into the back of the tbi


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## Robot135 (Dec 22, 2018)

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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## Wrench97 (May 10, 2008)

Check the fuel pressure when the problem is occurring also, Ive seen plenty of electric pumps drop out after they have run a bit.


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## Robot135 (Dec 22, 2018)

Ok Will do the fuel pressure test after warm up and when the problem is occurring


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## wolfen1086 (Oct 4, 2007)

when I 89 did that it was a faulty Injector spraying out the side due to a failed "O" ring on the left injector


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## Robot135 (Dec 22, 2018)

Fuel pressure is good and steady after warm up vacuum is good and steady


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## Corday (Mar 3, 2010)

Possibly dropping to many RPMs when coming off fast idle and reaching operating temp.


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