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2003 Denali XL code P071/P074 comes on and off the last month

Check engine light came on, code read at Autozone put a can of Seafoam in tank and light went off a day later. Light came back on a week later. Cleaned Mass Air Sensor and replaced air filter, ran MAS cleaner though when running light off. Ran truck for few hundred miles light back on. Changed Mass Air Sensor- no change in light status.

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6ya6ya
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Posted on Jan 02, 2017

chrischronic
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SOURCE: 0171 and 0174 codes

check all vacum lines starting with the pcv valve vacum line. check while engine is running ,lisen for air leak.if u have a vacum leak then this will set these codes.

Posted on Jan 22, 2009

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SOURCE: 91 LEGACY STARTED RUNNING ROUGH

The cylinders are numbered as on the spark pack you changed. You might have done better putting the seafoam in the tank as an injector cleaner. Not sure why you changed so many parts, you seem to know how to get the codes from test connector lead hookup and the blink pattern. You might also want to check the fuel rail pressure and the crank and cam angle sensors. Before replacing the injector, swap the #4 injector with the adjacent one and see it the code moves with the injector or stays put. If the code stays on #4, then check the injector wiring, if it moves clean or replace the injector.

Posted on Mar 21, 2009

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