Code P0171 seems false

2003 GMC SONOMA
225,396 MILES • 2.2L • 4 CYL • 2WD • MANUAL
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THE_WIZZARD
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The truck has a hard start condition if left sitting more than a day without starting. Whether cold or warmed to operating temperature. It puffs black smoke and smells rich. when revved up, the black smoke gets thicker and leaves sense carbon stains where the exhaust hits the ground. Sometimes I do have to cycle the fuel pump a couple times to get it to hit. And it will start a couple to four attempts later. MAF has been cleaned, no obvious vacuum leaks (I can normally hear those). I would normally replace the coolant temperature sensor, but this one is supposed to run the gauge and send to the PCM. And the gauge seems right. Suggestions or questions?
Apr 2, 2019 at 5:25 PM
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JACOBANDNICKOLAS
  • ASE Certified Mechanic
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  • ASE Certified Mechanic
Welcome to 2CarPros.

I agree, it doesn't seem right, but I think it is. Since you are seeing black smoke, the fuel mixture is too rich. The computer is compensating for a lean mixture. With that in mind, I think one of the following is most likely the issue.

Vacuum leak at intake.
PCV system vacuum leak (check all hoses.)
Injector o-rings.
Air induction tube leaks.
Exhaust leak before the O2 sensor.

By the way, I checked and the ECT sensor is for the computer as well. Have you checked to see what temperature it's reading when cold?

Let me know.
Apr 2, 2019 at 8:05 PM
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