P0301 Troubleshooting Logic

[Irun]

I've looked through a few threads here and didn't see anything that showed a progressive path to troubleshoot a P0301 code, without throwing parts at the Jeep. That said, I'd like to bounce this off you all and see what your thoughts are. Thus far, here's a summary of the steps taken:

1. Verify the plugs and coil were good (Visual inspection and Spark plug tester) - Even though the plugs are relatively new, less that 10k miles, I tested each plug and coil pack boot for spark, and they were fine;
2. Verify no intake, or exhaust, leaks (Smoke test) - Used a smoke machine to check the intake manifold and #1 injector O-ring, no significant issues there. Also, checked the manifold bolts and tightened a couple that were slightly loose.
3. Check injector Pulse (Stethoscope and Noid light) - Put a stethoscope on the injector #1 (Checked the others as well) and heard a strong and consistent injector pulse. Placed a Noid light (Bosh Type 2) and saw a pulsating/consistent flashing light.
4. Compression Test; Compression numbers were all between 170 and 165. While these numbers seem a little high, likely the gauge, the spread was good, with no more than 5psi variation.
5. Leak Down Test - This was a royal PIA, but the numbers were all good as well:

• #1: (leak down) 75/80 (pressure) = 6.25% leakage
• #2: 78/80 = 2.5% leakage
• #3: 75/80 = 6.25% leakage
• #4: 78/80 = 2.5% leakage
• #5: 78/80 = 2.5% leakage
• #6: 78/80 = 2.5% leakage

After the Compression and Leak Down Tests, because I had them, new Autolite APP985 plugs went in, gaped at.035.

Next on my list, when I get my scanner back from a buddy that borrowed it, is to do a Camshaft Position Sensor cam sync test. The target range is + or - 10 degrees, with 0 degrees being ideal.

Thoughts?

For those that may have to go through this, here's a list of the tools I used:

- Compression tester this one has the deep adapter needed for our 4.0l engines: https://www.amazon.com/dp/B08XR1PBPM?tag=wranglerorg-20
- Stethescope: Nothing special here, but it worked https://www.amazon.com/dp/B0DQXZW7BZ?tag=wranglerorg-20
- Leak Down Test Kit (Had to use the deep adapter from the compression test kit); https://www.amazon.com/dp/B0030EVL60?tag=wranglerorg-20
- Noid Light Tester (Using the Bosch Type 2 connector): https://www.autozone.com/p/oemtools...8078?msockid=2b6824c99030683419da315f919d692e
- Spark plug/Coil Tester: https://www.amazon.com/Lisle-20610-Inline-Spark-Tester/dp/B0002STSC6/?tag=wranglerorg-20

 

[macleanflood]

Coil can be ohm checked.

Is it consistently 301 or does it vary to 1-6 or 300?

-Mac

 

[Irun]

Coil can be ohm checked.

Is it consistently 301 or does it vary to 1-6 or 300?

-Mac

I did have one instance where it was a random misfire code, but only once. Other than that, it's consistently cylinder #1.

 

[macleanflood]

I'd swap injector 1 and 2 and see if it moves.

-Mac