Po305 Misfire Cylinder 5

[Dantheman-2003]

2008 GMC Sierra 1500, 5.3 Vortec. On the clock about 180k miles. Started running a little rough then check engine light comes on. Run the scanner, po305 misfire cylinder 5. I pulled the plug and it looked ok. Replaced it with a different one, no change. Moved some wires around, no change. Replaced coil pack, no change.

Any thoughts on the next move?

 

[Dustin Jackson]

@Dantheman-2003 Is it making any concerning sounds?

 

[Dantheman-2003]

@Dantheman-2003 Is it making any concerning sounds?

@Dustin Jackson - No concerning sounds in terms ok knocking etc. This truck has ran excellent since ownership never had an issue. This morning, Engine turns over just fine but with rough idle and flashing CEL.
1. I'm suspect of the plug because I cheeped out and got the whole plug and wire set off eBay "AC Delco". As others have mentioned maybe a fake set. I already had one fail on cylinder 8, cracked porcelain. Now on Cylinder 5 same thing and same symptoms. I'm headed to O'reilys to get a new plug then work backwards from there.

2. My next move if it's not the plug is the fuel injector.

 

[OR VietVet]

You could move plugs too.

 

[Dustin Jackson]

Could move the plug, wire, and coil and see if it follows. It sounds like you are on the right track, at least it doesn't sound like a mechanical problem

 

[Dantheman-2003]

Good suggestions. I will try and swap 1 and 5 and packs to see if it follows. Otherwise I will move on the the fuel, compression etc. I've heard others say could be o2 sensor, but I thought it had its own code. Po305 is specific to C5 misfire. Thanks for the inputs!

 

[OR VietVet]

If you do a compression test, you should have all plugs out. If you want a short cut, remove #3 and #7, each side of #5 and do the compression test and compare. Check for a vacuum leak too. I still say, swap the #5 plug with #3 plug, easier to get to, and see if misfire follows.

 

[Dantheman-2003]

UPDATE: I hope someone can find some humor here. I’m standing there over the engine bay contemplating my next move. Compression test first? Or fuel pressure test? Maybe start swapping wires and coils?

I’m ready to pull the trigger, coveralls on and all. So I look down and at a glance see my air filter indicator laying there at the bottom of the engine bay! WTF? Anyhow… all fixed now. Smooth operator all codes cleared. Back on the road.

Hope everyone has a great weekend go 9ers!

Dan

 

[OR VietVet]

That is weird. Even that air has to go thru the MAF.

 

[donjetman]

That is weird. Even that air has to go thru the MAF.

Right