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Old 01-26-2011, 02:22 PM   #1
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Default P0300- multiple cylinder random misfire

I have a JGP silverado with a 4.8L supercharged engine. A month ago I put on a set of pacesetter headers and ORY. today the check engine light started blinking and I the truck started running really rough. P0300 is the only code so I am assuming the problem doesnt have to do with a specific cylinder otherwise I would get a P0301 thru P0308 telling me which cylinder was the problem. What would cause this issue?

I could really use some help bc I am at work, its starting to snow, and I have no other way home. thanks.
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Old 01-26-2011, 02:27 PM   #2
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What are your plugs gapped at? I think for blower applications they reccommend .030 - .035 iirc. If I'm wrong I'm sure someone will come in here and yell at me.
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Old 01-26-2011, 02:44 PM   #3
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stock plugs. truck only has 49k miles on it
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Old 01-26-2011, 02:51 PM   #4
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I wouldn't rule out a single cylinder. Go back and pull all your spark plug wires off the plugs, check to make sure all the plugs are in tight, then put the wires back on and make sure they're seating properly. Check to make sure one of the wires didn't get burned up as well.

I'd also check the MAF to see if it's dirty.
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Old 01-26-2011, 05:45 PM   #5
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plugs/ wires are fine. just drove it home. realized that the engine light turns off when i was idling at a stop light, then comes back on soon as I hit the gas. I just got a tank of gas yesterday, premium from Shell, so it could be bad gas. I bought a bottle of HEET and put that in it. hopefully its just water in the gas. tomorrow im gonna check the fuel pressure. if the fuel pressure is fine, then im gonna run the tank empty and get some good gas to see if that helps. if the fuel pressure is low then im guessing its either a fuel pressure regulator or fuel filter. what do you guys think?
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Old 01-26-2011, 05:51 PM   #6
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Fuel filter could be causing an issue, but I'd double check to see if what Scott said is causing it. We've had issues with Shell gas for years, so that could be it as well. Replacing the filter won't hurt anything even if that isn't the problem, and you can get one at the dealer for 20 bucks.
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Old 01-26-2011, 06:08 PM   #7
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i read somewhere that in 2004 chevy got rid of the inline fuel filter and replaced it with one in the fuel tank. does this sound correct?
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Old 01-26-2011, 06:28 PM   #8
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one other thing i forgot to mention. I installed keyless entry on my truck yesterday. As soon as the problem occurred today the first thing i did was disconnect the keyless entry. obviously that didnt fix it. I found this online:

Info - Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems #02-06-05-004A - (Jan 9, 2004)
Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems

2004 and Prior GM Passenger Cars and Light Duty Trucks

2003-2004 HUMMER H2

2004 and Prior Isuzu Light Duty Trucks

This bulletin is being revised to add the 2004 model year and include specific DTCs in the title line. Please discard Corporate Bulletin Number 02-06-05-004 (Section 06 - Engine/Propulsion System).

General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles.

These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Over time, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.

Important

Engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. Because of this, it has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition.

Dealers must be aware of this issue and take note of the wiring on vehicles with alarm systems that come in for repair, particularly for catalytic converter damage that seem to have no known root cause.

so this is saying my keyless entry caused the p0300, but now that the keyless entry is disconnected, how do I fix the problem? already tried clearing the code a couple of times.
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Old 01-26-2011, 09:00 PM   #9
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Quote:
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i read somewhere that in 2004 chevy got rid of the inline fuel filter and replaced it with one in the fuel tank. does this sound correct?
That is correct, 2004 and up is in the tank.
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Old 01-26-2011, 09:04 PM   #10
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AFAIK, all trucks have a large particulate screen in the tank - not necessarily a filter I don't guess - but they have something to keep large obstructions from getting into the fuel line.
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Old 01-26-2011, 09:04 PM
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