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Discussion Starter #1
I have an ‘08 Redline, 34K miles. Check Engine Light always comes on after reset. Takes about 60 miles of driving. Code shows all cylinders misfire at low RPM. Code clears when aggressively driven. So far...new AC plugs, 4 new coils, intake induction cleaned, fuel additives, new gas cap, same code appears. Also did a smoke test for leaks. Nothing found. Kind of frustrating. Any help is appreciated.
 

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Knowing the specific code(s) is critical for remote diagnosis.
 

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Some probable causes: Spark plugs, Vacuum leaks, Fuel pump or fuel pressure sensor, Mass airflow sensor, Crankshaft position sensor, Emissions system problem, Blown head gasket, ECU failing, Bad tune.
 

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Discussion Starter #8
Some probable causes: Spark plugs, Vacuum leaks, Fuel pump or fuel pressure sensor, Mass airflow sensor, Crankshaft position sensor, Emissions system problem, Blown head gasket, ECU failing, Bad tune.
Most of the mentioned are good as per my initial write up. Head gasket is fine, no leaks at all. Mass airflow seems ok too. Never heard of Crankshaft position sensor. Something to look at. Fuel pressure sensor is possible too. Thank you.
 

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What spark plugs did you install? How do you know that the mass airflow sensor is good. Did you install an aftermarket intake?
 

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From the service manual:

If any other DTCs are present, fix those first. If the engine exhibits any unusual noise, fix that first.

Beyond coils, plugs, and injectors, any of which should produce a cylinder-specific misfire code, the following are listed as possible engine-related causes:
  • Engine vacuum leaks
  • Fuel pressure too high or too low
  • Contaminated fuel
  • Restricted exhaust system
  • A damaged reluctor wheel
The following are listed as possible non-engine-related causes
  • A tire or wheel out of round or out of balance
  • Variable-thickness brake rotors
  • An unbalanced drive shaft
  • Certain riugh road conditions
  • A damaged accesory drive component or belt
Occuring at low speed and clearing when driven hard suggests either a vacuum leak or high fuel pressure.
 

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Discussion Starter #11
From the service manual:

If any other DTCs are present, fix those first. If the engine exhibits any unusual noise, fix that first.

Beyond coils, plugs, and injectors, any of which should produce a cylinder-specific misfire code, the following are listed as possible engine-related causes:
  • Engine vacuum leaks
  • Fuel pressure too high or too low
  • Contaminated fuel
  • Restricted exhaust system
  • A damaged reluctor wheel
The following are listed as possible non-engine-related causes
  • A tire or wheel out of round or out of balance
  • Variable-thickness brake rotors
  • An unbalanced drive shaft
  • Certain riugh road conditions
  • A damaged accesory drive component or belt
Occuring at low speed and clearing when driven hard suggests either a vacuum leak or high fuel pressure.
Thank you for the suggestions.
 

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Discussion Starter #12
What spark plugs did you install? How do you know that the mass airflow sensor is good. Did you install an aftermarket intake?
I do t have the spec in front of me. AC Delco spec plugs. Service center said the airflow sender was ok.
 

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Knock could occur with timing advanced too far or fuel mixture too lean. Rich mixture slows down the flame propagation and would most likely not knock. High carbon build up could make it knock. Low rpm misfire is most commonly a contaminated or failing MAF sensor. A bad MAF will modify the fuel mixture.
 

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Discussion Starter #14
Knock could occur with timing advanced too far or fuel mixture too lean. Rich mixture slows down the flame propagation and would most likely not knock. High carbon build up could make it knock. Low rpm misfire is most commonly a contaminated or failing MAF sensor. A bad MAF will modify the fuel mixture.
Car runs like it’s at Seabring. No knock, no miss, runs like a champ. You would never know there was an issue except the light comes on. I’ll look into the MAF. Thank you.
 

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Wouldn't knock trigger a DTC? P0326 or P0331?
 

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Do you have a CAI???? If so, do you have an oiled air filter? 99% do... If so, MAF could be the problem. The oil gets on the filament and causes issues. Do you have a GMPP tune? If so, are the wires crimped or soldered? If they're crimped, tear them apart and solder them...this could also cause an issue, but not usually setting a misfire code. Don't use any fuel additives!!! I'm a firm believer that Techron destroyed my HPFP. The stuff is very sticky and with DI, you could blow a golfball through a garden hose, so nothing is stuck in your injectors. At 34k I doubt it would be dirty intake valves. Nothing really cleans them because nothing touches them so they cake up with carbon, but that's usually around 60-80k. Although if you've been running regular unleaded (87 octane, 91 is supposed to be used) this could cause them to cake earlier. If it's your HPFP you'll get a code too rich or too lean...usually a p21##
 

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Discussion Starter #18
Do you have a CAI???? If so, do you have an oiled air filter? 99% do... If so, MAF could be the problem. The oil gets on the filament and causes issues. Do you have a GMPP tune? If so, are the wires crimped or soldered? If they're crimped, tear them apart and solder them...this could also cause an issue, but not usually setting a misfire code. Don't use any fuel additives!!! I'm a firm believer that Techron destroyed my HPFP. The stuff is very sticky and with DI, you could blow a golfball through a garden hose, so nothing is stuck in your injectors. At 34k I doubt it would be dirty intake valves. Nothing really cleans them because nothing touches them so they cake up with carbon, but that's usually around 60-80k. Although if you've been running regular unleaded (87 octane, 91 is supposed to be used) this could cause them to cake earlier. If it's your HPFP you'll get a code too rich or too lean...usually a p21##
I pulled the MAF and cleaned with contact cleaner for circuit boards. Don’t drive the car a lot. Disconnected the battery to reset the light. I’ll keep you posted. Thanks.
 
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