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30 Posts
Discussion Starter #1
03 avalanche 5.3L 1500 after cam and head upgrade, Can bank 2, if the valves aren't set right, cause bank 1 to misfire and run lean? Its across 1,3,5 and 7, not just one cylinder.. I've tried everything else and I'm at a loss.

2,818 Posts
Okay, let's start with what you stated: "Can bank 2, if the valves aren't set right, cause bank 1 to misfire and run lean? No, each bank is separate except the intake manifold connection. Its across 1,3,5 and 7, not just one cylinder"? Sounds like more like a air / fuel delivery issue such as a intake manifold gasket no installed properly or improper intake manifold gasket.

Chevrolet Code P0300 Definition
Random/Multiple cylinder misfire detected.

What Does Chevrolet P0300 Mean?
Chevrolet code P0300 indicates that one or more cylinders are experiencing misfires. A misfire occurs when an insufficient amount of fuel is burning in a cylinder. The efficient burning of fuel is essential to engine operation as the combustion of fuel is what provides the energy to power the engine in your Chevrolet.

A misfire from one or more cylinders can be caused by many reasons from a faulty ignition system, fuel system or internal engine failure. When P0300 occurs it should be fixed immediately as long term driving with engine misfires could cause consequential damage to the engine.

Many times P0300 occurs when there are worn out spark plugs, spark plug wires, or a faulty ignition coil.

Chevrolet P0300 Symptoms

  • Check Engine Light is on
  • Engine runs rough and shaking
  • Lack of power from the engine
  • Fuel smell from the exhaust
  • Hesitations/Jerking when accelerating
Chevrolet P0300 Causes (* = Most Common)
  • Faulty or worn spark plugs *
  • Faulty spark plug wires or coils *
  • Distributor failure *
  • Faulty fuel injector *
  • Vacuum leak
  • Low fuel pressure
  • Camshaft sensor defective
  • Crankshaft sensor defective
  • Engine timing off
  • Leaking head gasket
  • Low engine compression
  • Poor quality fuel

Chevrolet code P0300 should be repaired immediately. Ignoring this error could result in ignition failure, catalytic converter damage

Chevrolet Code P0300 Common Diagnosis Mistakes

Loose fitting electrical connectors and broken or disconnected vacuum hoses are often overlooked.

How To Diagnose Chevrolet Code P0300
* Use a scan your Chevrolet to verify P0300 is the only code present. If other codes are present, they must be addressed first.

* Check for loose connectors at the ignition coils or for damaged wiring. Look for loose engine ground wires as well.
These can cause rand misfire conditions. Tighten or connect where necessary.

*Check the condition of your spark plugs and spark plug wires. Worn and old spark plug wires are common causes of random misfires.
Replace spark plugs and wires if needed and recheck for misfires.

* If you have determined that your ignition system is operating correctly, there may be a problem within your fuel system that is causing the
random misfires. The following should be checked to ensure the engine is getting the proper amount of fuel:

* Check fuel pressure. Low fuel pressure can cause intermittent misfires on multiple cylinders. When the pressure is below the specification, the
engine does not receive the proper amount of fuel and will start to lean misfire. The fuel pump or fuel pressure regulator could be the source of
the low fuel pressure.

* Check that the fuel injectors are functioning properly and activating. Random misfires can be a sign of faulty or clogged fuel injectors that need
to be replaced. Also check that the fuel injector wiring is not damaged and is connected properly.

* If the ignition system and fuel system checks out you may want to perform an engine compression test and leakdown test to see if there are any
mechanical problems causing your misfire.

Some common mechanical problems that cause misfire can be:
  • Broken valve spring
  • Broken piston ring
  • Worn valve guides
  • Burned valve
  • Timing chain or belt skipped tooth and engine is off time.

39 Posts
You said you replace the heads. Did you do a swap to the LS6 243/799 heads? If so did you make sure they were milled .030? You will have low compression if the heads are not milled.
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