A wet test might be worthwhile doing too. Then compare the wet & dry readings.

Edit: When testing compression, disable the ignition coil, remove the fuel pump relay, and prop the throttle wide open. For the wet test, just before cranking, squirt a ~tablespoon of motor oil in each cylinder.

 

Okay performed two more compression tests. One wet and one dry.

The dry numbers were a bit higher than yesterday. It way had might have something to do with driving 55 miles today. Cylinders 1, 3 & 5 posted between 150 and 157 psi. And cylinders 2, 4 & 6 yielded between 130 and 139 psi. The wet tests didn't show much of a change. 1, 3 & 5 increased by about 5-7 psi. 2, 4 & 6 went up by 4-6 psi each cylinder. So the difference in the two banks is about 20 psi.

So what's next? Burnt exhaust valve(s).

 

I dont beleive its valves cause of the way your compression test yeilded.You have one bank running good compression and other not so good.

 

I have to agree ^^

The wet numbers are not indicating anything unusual. Have you checked cylinder leakage? That test is more targeted at leaky valves. Compression is more for rings. Have you checked fuel trims? Post them if you have them.

 

Interesting you mentioned possible leaky valves. I was just researching this very subject. As far as fuel trims, I guess in order to get the STFT and LTFT numbers I'll need to take it in for diagnosis?

According to OBD-II Trouble Codes - DTC Codes Car Repair, I've eliminated the following possible causes:

Faulty spark plug or wire (4 months old)
Faulty coil pack (4 months old)
Faulty fuel injector (5 months old)
Faulty catalytic converter (high flow installed 6 months old)
Poor compression (just tested)

So, this leaves me the following:

Faulty O2 sensors
Burned exhaust valves
Running out of fuel
Defective computer

Other than what was just said, are there any other tests I can do on those items just listed to see if they are working properly (besides the converter)?


Thanks again guys! I feel like I'm sooooooooooo close to solving this problem.

 

Have you tried swapping plugs & wires with another cylinder? ie trade plugs & wires with cylinder #4. Then check DTC's and see if still sets P0306, or follows the swap.

Edit: Fuel trims you can get right from the scan tool, even the el cheapos show it. It will tell if a bank is running rich or lean, and how much the PCM is compensating.

 

I did try swapping wires but it was awhile back, maybe last fall. The misfire did not move to another cylinder but I will do this again and drive it tomorrow to an from work to see if it makes a difference. Also, can I check the wires for a specific amount of resistance? Shouldn't there be about 4-5k ohms of resistance per foot of wire?

I'll see how to check my fuel trims with my scan tool and report back.

 

Checking resistance on the wires with an ohmeter is pretty much a worthless test, (especially in your case with a slight misfire). Many times when they get an actual load going through them is when they fail, same thing with spark plugs. Post the STFT & LTFT numbers for both banks, make sure it's at operating temperature. P0306 is the only DTC you're getting?

 

I just plugged in my scan tool and it's reading an error code of P0306 AND, haven't seen this since I bought the truck last year, an incomplete monitor - catalyst.
Hmmm. Would a high flow catalytic converter cause the incomplete monitor error?

My scanner, Actron CP9125, doesn't show fuel trim percentages (really cheap scanner).

 

Incomplete monitor will not cause a misfire. Performing step #7 of the General Motors Driving Cycle will force the monitor to run and complete its test. You must duplicate the step exactly as written.

Edit: Your Actron CP9125 is not a scan tool. It's an entry level code reader, that's all it does, no streaming data.