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2000 Chevrolet Blazer 4.3L P0171 and P0300 Fault Codes: Lean Mix & Misfire Diagnosis

Model: 2000 Blazer Fault Code: P0171 Posted: 2011-11-22 09:22

I own a 2000 Chevrolet Blazer with a 4.3L V6 engine, 4WD, 4-door configuration. The check engine light is on, and the vehicle runs smoothly during cold start and warm-up cycles. However, after the engine reaches operating temperature and the loop closes, it begins to run roughly with a noticeable lean smell. Current Diagnostic Trouble Codes (DTCs): - P0171: System Too Lean (Bank 1) - P0300: Random/Multiple Cylinder Misfire Detected (with one pending) - P1133: Oxygen Sensor Malfunction (possible) I've already replaced the fuel pump, fuel filter, PCV valve, spark plugs, ignition wires, distributor cap, and rotor. Despite these changes, the symptoms persist. Any insights or troubleshooting steps for this combination of codes would be greatly appreciated. Thank you, John Haines

Related fault codes
P0171P0300
Comments (7)
Anonymous 2011-11-22 19:43

What are your fuel trim readings? Specifically, what is the short-term and long-term fuel trim for Bank 1 and Bank 2?

Anonymous 2011-11-25 12:46

Fuel trim data: Bank 1 short term = 50%, Bank 1 long term = 24.219%; Bank 2 short term = -2.344%, Bank 2 long term = 5.469%. No fuel pressure gauge available at this time.

Anonymous 2011-11-25 23:55

This strongly suggests a fuel delivery issue, possibly related to the fuel injection system or fuel pump performance.

Anonymous 2011-11-28 08:39

The symptoms match what I've seen with my own 2000 Blazer equipped with a spider-type fuel injection system. After replacing all standard components, I suspect the spider module is failing—this is now my next step for repair.

Anonymous 2011-11-30 10:09

Multiple online forums indicate that the spider fuel injection system may be the root cause in vehicles like this, especially when combined with P0300 and lean codes.

Anonymous 2011-12-06 16:20

I previously had a 2002 Chevrolet Astro with identical symptoms—P0300 during driving or idle. I found that the right bank showed over 2% allowable misfires in cylinders 2, 4, and 6. After checking live data, oxygen sensor readings were abnormally high. Replacing just one O2 sensor resolved the issue for under $40—worth a check before investing more time or money. Good luck with your diagnosis!

Anonymous 2011-12-06 21:18

John, could you please share what ultimately fixed your P0171 and P0300 issues? Any updates on the solution?