Recently purchased 02 silverado and was throwing multiple codes. Fixed everything aside from dreaded p0300 code. Multiple misfires. New plugs,wires,ect sensor,cleaned maf sensor and checked cat converters. Oil looking substance I believe to be unburned gas is on threads of plugs on passenger side from cylinders 2,4,6&8. Any feedback from someone with situation experience would be greatly appreciated

 

if theres anything on the plugs its prob coming from the valve covers and leaking down and as your unscrewing the plug youll be "threading" the plug in the oil thats leaked down. whats your gas pressure

 

Engine clean. No leaks and fluid is covering entire spark node and inner thread. I believe it to be unburned gas due to misfires causing it to run too lean/rich. Air/fuel ratio is off. It runs fair enough I just don't have power when needed. For instance if I stop on steep incline I cannot make it up, I have to back down and get a run at it. And forget pulling a trailer. Full power kicks in time to time

 

 

New fuel filter and removed egr valve and installed intake and exhaust block plates.

 

Hello.
So, you have 'wet' plugs on one side, right?
Can you check your fuel trims, both shrot term and long term. This can tell alot.
You may have a vacuum leak, intake obstruction or leaking injector.

Check the fuel trims for start.

Hope that will help.

 

Ok my experience with P0300

2003 2500HD 4x4 with 6.0

First time took me months to figure out. Finally found out that its common due to timing chain stretching over time. engine had over 160000.
Took it to my GM guy, he hooked it up to computer and did the relearn on the ECM, Fixed

This time truck has sat for about 5 months with about 3/4 tank of gas.
Now getting P0300 and P0134
Changing plugs, added Octane Boost and Seafoam. Gonna run til almost empty then fill and see what happens.
I'll keep you posted.

 

No computer relearn procedure will fix a mechanical problem. If a timing chain was stretched so far that it’s causing misfires, it needs to be replaced. Your GM guy was either blowing smoke or hoping for the best with a relearn and I’m curious what procedure was actually performed. If a relearn did fix it, the timing chain being stretched was not the issue.

There are many possible causes of random misfires. On these engines in particular, the coil grounds are known weak points and cause P0300 to set. They are prone to corrosion and the wire breaking at the eyelet crimp. They are located at the ends of the cylinder heads, front or rear depending on the bank.

Since you’ve already done plugs, other possible causes are:

Plug wires (if you didn’t also change them)
Poor fuel quality
Sticking injectors
Weak fuel pump or restricted inline fuel filter (if equipped)
Leaking intake manifold gaskets or vacuum hoses
EGR valve sticking open
Dirty throttle body

Check freeze frame data - if code set at idle, the throttle body or EGR would be likely causes.

The P0134 is either the sensor itself or wiring.

Good luck.