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P0305 and P0171 Fault Diagnosis on 1999 Chevrolet Malibu V6 - Causes and Solutions

Model: 1999 Chevy Malibu Fault Code: P0171 Posted: 2009-07-18 07:19

What causes both P0305 (Cylinder 5 Misfire) and P0171 (System Too Lean) on a 1999 Chevrolet Malibu with a V6 engine? I recently replaced the spark plugs and ignition wires approximately one month ago. Despite this, the fault codes have reappeared. I have since also replaced the coil packs. I used high-quality spark plugs and wiring components. I can confirm that cylinder #5 is firing properly. However, I've noticed a significant amount of water coming out of the exhaust pipe—could this indicate a failing catalytic converter or a more serious exhaust system issue? Any insights or troubleshooting steps would be greatly appreciated. Thank you, Jesse

Related fault codes
P0171P0305
Comments (3)
Anonymous 2009-07-19 06:51

Did the P0305 and P0171 codes appear after installing new spark plugs and ignition wires? Have you checked or replaced the distributor cap and rotor? Were high-quality components used? Check for vacuum leaks, especially on Bank 1 (driver's side manifold). Also, try swapping the injector in cylinder #5 with a known good injector from another cylinder to see if the misfire code changes. Confirm that cylinder #5 is actually receiving spark. Good luck—please update us on your findings.

Anonymous 2009-07-19 10:57

The P030-than codes started appearing several months after I replaced the plugs and wires. I have since replaced all coil packs. I used quality spark plugs and ignition wires. I am certain that cylinder #5 is firing correctly. The water coming out of the tailpipe raises concern about a failing catalytic converter—could this be the root cause? Thanks for your helpful advice. Jesse

Anonymous 2009-07-20 06:38

While a clogged or restricted catalytic converter is possible, it typically does not trigger P0171. A lean condition like P0171 is more likely due to vacuum leaks or injector issues. First, perform an injector swap on cylinder #5 and inspect for vacuum leaks. If the codes persist, then exhaust system restrictions may be a factor—but a blocked catalytic converter alone won't cause P0171.