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2000 Pontiac Grand Prix OBDII read PO300

Tiny
JIQUILPENO
  • MEMBER
  • 2000 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 128,500 MILES
Grand Prix GTP Supercharged read a code of PO300. I put 87 octane will this trigger this code.
Thursday, February 18th, 2010 AT 10:19 PM

7 Replies

Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
DTC P0300: Engine Misfire Detected

87 Octane most likely not the cause of this. Check ignition wires and ignition coil. Check ground wires, MAF sensor, air induction system, fuel pressure, injectors and EGR valve. Faulty oxygen sensors may also cause misfire.
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Thursday, February 18th, 2010 AT 10:40 PM
Tiny
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Before I had a PO140 & PO171 and I repaired a vacuum leak located on the Fuel Press regulator. Replaced the spark plugs and cleaned out the EGR valve and the MAF sensor. Fuel PSI reads 44psi at idle and 53psi when you accelarate or disconnet the vacuum line on the FPRegulator. Car runs fine, only missfires under boost/load. Codes were erased after these codes with the exception of the O2 senor #2. After these the only code im getting is PO300. I went to the dealer to get it Diagnose and I explained all these to them and they came out with filling it up with 91 Premium octane.
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Thursday, February 18th, 2010 AT 11:03 PM
Tiny
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Supercharger may be weakening a bit causing a slight misfire. Can you feel the misfire or is it just enough to kick the engine light on?
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Thursday, February 18th, 2010 AT 11:07 PM
Tiny
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I can feel it under load only, it sputters then it kicks in. But if you drive it regular its all good to go.
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Thursday, February 18th, 2010 AT 11:15 PM
Tiny
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Did you ever replace the ignition wires? What brand and gap on the plugs? Spark plug manufacturers and tuners suggest reducing the factory recommended spark plug gaps on supercharged engines because using a too wide gap can result in misfires, loss of power, poor fuel economy, premature spark plug failure, uncontrolled exhaust emissions and possible engine damage. If you use your supercharged street engine for commuting, keep in mind the spark plug gaps progressively erode and widen with everyday use. Did using the higher octane help anything? Did the code come back or misfire occur under load with 91 octane?
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Friday, February 19th, 2010 AT 12:16 AM
Tiny
JIQUILPENO
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Spark plug wires were replaced about a year ago and were inspected. They still look new with no signs of heat damaged Spark plug wires AC Delco. Spark Plugs were replaced a couple of days ago when the car had the same syptoms. Replaced with AC Delco Iridium 41-101 Gap to Manuals specs.060
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Friday, February 19th, 2010 AT 12:38 AM
Tiny
JIQUILPENO
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I forgot to answer the gas question. No I have not tried it with 91 octane yet I am waiting to get rid of that fuel and I will see what happens.
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Friday, February 19th, 2010 AT 12:40 AM

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