Misfire! Misfire! Misfire!

[flashlight_65]

My check engine light popped up as I was driving to work and started blinking when I drove uphill on my way home the other day so I went to O'Reillys to see what code popped up (P0308, misfire in cylinder #8.)
Since the 'hoe has 119'000 miles and I dont know when the the last time the plugs or wires were changed. Before I did that I put seafoam through the vacuum line and in the tank. After I changed the plugs and wires (gapped the plugs to .040) the CEL went out, happily I drove around for a bit and it felt a bit smoother but still didn't "feel" right then BAM! CEL back on, so i took it back to O'Reillys and the same code showed up, so i swapped coil #8 with coil #4 and had it cleared out. After driving around again CEL came up again same code P0308. If it's not the plugs, wires or coil where should i look next? The fuel filter is a few months old but other than that im stuck. Any ideas?

Vehicle:
2002 Chevy Tahoe LS
5.3 liter
4x4

 

[BubZX]

Could be a bad injector

 

[TacHoe]

sounds to me like a bad coil or two bro... if you swap between cylinders and still get the code I always thought that meant the coil was bad

 

[BubZX]

Did it come up cylinder 4 after u switched the coils?

 

[Sprayed99]

My check engine light popped up as I was driving to work and started blinking when I drove uphill on my way home the other day so I went to O'Reillys to see what code popped up (P0308, misfire in cylinder #8.)
Since the 'hoe has 119'000 miles and I dont know when the the last time the plugs or wires were changed. Before I did that I put seafoam through the vacuum line and in the tank. After I changed the plugs and wires (gapped the plugs to .040) the CEL went out, happily I drove around for a bit and it felt a bit smoother but still didn't "feel" right then BAM! CEL back on, so i took it back to O'Reillys and the same code showed up, so i swapped coil #8 with coil #4 and had it cleared out. After driving around again CEL came up again same code P0308. If it's not the plugs, wires or coil where should i look next? The fuel filter is a few months old but other than that im stuck. Any ideas?

Vehicle:
2002 Chevy Tahoe LS
5.3 liter
4x4

well simple diagnostic testing tells you that you have to have the following to cause a misfire.

Coil, plug, wire, or fuel.

I would swap a injector out to the other side....anytime you switch anything do it from odd to even or even to odd. Some codes will show bank1 or bank2 meaning even side or odd side of the engine.

Take a coil from say #1 and swap it with #8 then recheck.... If it still pops the code do the same with the injectors.

But I vote injector. You can ohm check it, but given the mileage it could be also so gunked up that it is restricting the spray orfice.

 

[flashlight_65]

Thanks for the help everyone,it ended up being a bad injector. Since I changed the injector I've still noticed the engine had a small stutter at idle it's like it bogs down a tiny bit and catches back up even when the enGgine is warm. I cleaned out the throttle body with carb cleaner, the MAF sensor with MAF cleaner, cleaned and re-oiled the intake filter.

I sprayed carb cleaner around the injectors and intake manifold and it didn't idle any different. My guess is it could be the intake gasket needs to be replaced. Any ideas?