Cylinder 5 Misfire

[seadoojetski]

Hey everyone, my name is Parker. I am having trouble narrowing down my misfire at idle issue nearly a year since I started the diagnosis.

2004 GMC Envoy SLT 4.2 L I6 4x4
Codes: P0305

211,000 miles
All spark plugs replaced (ACDelco 41-103)
All coils replaced (delphi)
Throttle body cleaned and idle learned
Exhaust manifold replaced
Intake manifold gaskets replaced
Fuel injectors replaced (Acdelco)
AIS solenoid replaced
Valve cover gaskets replaced

Standard cold compression test (innova brand tester) showed 175 psi on cylinder 5 compared to 180psi on neighboring cylinders

Misfire counts on my obd scanner increase rapidly for cylinder 5 (1 per second) while at idle in any gear. As soon as you step on the pedal and increase engine speed above ~1000rpm, the misfire counts stop rising. As another note, the misfires at idle are very uncommon when the engine is cold from sitting overnight.

I thought maybe I had a defective new coil, but swapping coils from 5 to 3 resulted in the code staying on cylinder 5. I am out of ideas here, wondering if anyone had any leads or something else to check

Another weird thing I noticed while plotting out my code history is the code started in the beginning as a P0300 and around a month after swapping the plugs and coils it finally manifested as a P0305 instead of P0300

 

[mrrsm]

Check out these Threads that cover using the ACDelco TEC (Top Engine Cleaner) in order to de-carbonize the Piston Heads, Valve Seats and loosen the Trapped Two Upper Compression Rings that due to their having a "Low Tension" become trapped within the Lands and Grooves of the Pistons, affecting compression and allowing an excessive amount of partially burned combustion by-products to contaminate the nether-regions of the "Boxy" Crank-Case-Oilpan.

Does your Oil Level Dipstick smell of excess Fuel? That is one of many symptoms that the "Black Mung" of Carbon is involved. The use of the ACDelco TEC is made easier with the Inline Engines by simply Parking the SUV outside away from People and Pets and in a well ventilated area and after pulling the COPs & Spark Plugs (disable ANY chance that the Engine will be Turned Over) and allowing the stuff to soak inside each cylinder for 2-3 Hours.

Then use a Turkey Baster to aspirate all of the Black Carbon Colored ACD TEC Liquid from all six cylinders prior to replacing the Spark Plugs to avoid Hydro-Locking the Engine and bending the Con-Rods by gradually turning over the motor with NO Plugs installed and catching the "Liquid Ejecta" with Blue "Scott" Towel Shop Rags.

ACDelco TEC is VERY High in Toxic VOCs (Volatile Organic Compounds) so by all means... avoid Breathing in the Fumes or getting this stuff on your skin.

Change your Oil and Oil Filter with Cheap Organic Oil and Cheap Filter and run the motor for 10-15 Minutes to clean out any detritus that will have contaminated the Oil in the Oil Pan. Then switch over to Mobil 1 5W-30 Motor Oil and either a Mobil 1 or K&M Oil Filter and give it a Road Test.

These Threads will prove very informative and useful in this quest:

gmtnation acdelco tec at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

 

[Mooseman]

Been there with Cyl#4. You seem to have done the same as me.

Very Slight Miss at Idle

Yesterday on the TB, at 117k km, saw the CEL come on and code came up for P0304. Fired up Torque and it was missing on cylinder #4 but only at idle or stopped at a light. It's not a big miss since I can't feel it at all and it's just a couple of misses per refresh cycle. While driving...

gmtnation.com

And 80k km later, I still have it. I just don't let it idle for too long.