FIXED 2014 Dodge Challenger 3.6L P0302

Background: Customer brought the car with a constant misfire only on cylinder 2. The car was at a different shop before it arrived to our shop. The invoice from previous shop stated they checked spark plug and coils. Then they replaced the PCM and it still did not fix the issue. I don't know how accurate this is because I am not familiar with that shop.

Since the car arrived to the shop, I have done the following things:
- Switched spark plug around from cylinder 2 to 4(no change)
- Switched ignition coil around from cylinder 2 to 4(no change)
- Switched fuel injector around from cylinder 2 to 4(no change)
- Installed smoke machine to verify for any vacuum leaks(no leaks detected)
- Verified compression with compression test on cylinder 2, 4, and 6(Passed, within spec)
- Verified compression with leak down test on cylinder 2, 4, and 6(Passed, within spec)
- Replaced 4 lifters and 4 rocker arms for cylinder 2(no change)
- Removed left cylinder head and had valves, guides, and seats replaced. Head was also pressure checked(no change...yes I did all that just to see the car misfiring on startup again.

I am willing to try just about anything to fix the issue. I am just about 100% certain that the issue is not mechanical and more electrical. LTFT 1 is sitting right a 0. LTFT is sitting at -7%.

COP design? Look for carbon tracking on plug and coil. Coil or plug wire not making good connection to plug. If wire type, swap or change plug wire.

Can you scope the coils?

It's not clear wether you do have injector pulse, coil firing etc..... Please make clear.

Can you scope ignition, injectors, go in cylinder.....?

When do you notice the misfire? At idle, while cruisng, at WOT? What is the Freeze Frame for P0302?

Sorry for the late reply guys. I've been extremely busy with other cars but I'll jump back onto the challenger for the rest of the week.

@Tyler
The misfire is felt on idle and when driving driving in lower RPM speeds. <1500 RPM. I watch the misfire counter when driving on the freeway and there are no misfires until I come to a stop. I've attached a screenshot of the Freezeframe.

@juergen.scholl
Yes I do have injector pulse. All coils are firing. I can scope out all those things tomorrow afternoon.

@scannerjohn
I swapped out all the plugs and coils with new NGK ones. The misfire is consistent on cylinder 2 with the old or new plugs/coils.

New things I've done since this post:
- Replaced PCM (Still misfiring on Cylinder 2)
- Replaced upper and lower intake manifold gaskets (Still misfiring on Cylinder 2)
- Replaced Throttle Body (Still misfiring on Cylinder 2)
- Replaced MAP sensor (Still misfiring on Cylinder 2)
- Replaced Crankshaft Position Sensor (Still misfiring on Cylinder 2)
- Checked catalytic converters to ensure they weren't clogged (Cats are fine)
- Swapped Bank 1 O2 sensor with Bank 2 O2 sensor (Still misfiring on Cylinder 2)
- Swapped Bank 1 camshafts solenoids and camshaft sensor with Bank 2 camshaft solenoids and camshaft sensor.
- Check harness and connectors for any corrosion or damage (Wires and connectors all look good)
- Load tested injector and coil wire from connectors to PCM (There was only a .02 voltage drop, nothing major)
- Fuel pressure was also tested and is hovering at 58psi

Today I went ahead and viewed timing data with my Zeus and I believe there may be an issue. I'm not 100% on what base spark and advance spark should be at idle but I have attached a screenshot of that info. If anyone has info they can sure, it would help me out so much. Image 1 is Smart Data while idling. Image 2 is Freeze Frame for P0302. Image 3 is Crankshaft Sensor waveform while idling.

Thanks for your help

Your scan data shows idle conditions. With a misfiring occuring the pcm will try to control the rpm by adjusting the timing. It does so because it is the quickest way to get the desired response, an IAC or a motorized throttle will react much slower. The graph shows what looks like a ~ 10⁰ base timing, something not unusual.

At this point I would consider to take a CLOSE look at the mechanical condition of the engine, the rpm range within which the misfire occurs raise suspicions of a (valve)sealing issue. Leak down tests as you performed are great to detect them in many cases but they're not 100% conclusive. A dynamic test, with the engine running, may reveal the underlying cause. You could do so with a vacuum gauge performing a running compression test, or even better, going in cylinder with a pressure transducer.

Thanks for the reply, Ricardo_Lira. I appreciate the screenshots.

I agree with Juergen and his suspicions of an engine mechanical problem. A quick and dirty direction test I've adopted (on this engine) is to look at the individual injector pulse widths at hot idle, in Park. This is an example I took from a '16 Town and Country 3.6L with a P0302:

drive.google.com/file/d/153KElpf-OMtviNZ...lU8/view?usp=sharing

The pulse width of the suspect cylinder is usually 100-200us shorter than the others. The Snap-On min/max graphs make this easy to spot.

If you see a similar kind of pulse width difference, I'd go directly to a relative compression test. Keep in mind that the RC won't catch every mechanical issue. But it's a great place to start. This is a relative compression waveform I took off the same Town and Country as above. Sync on #2. The low compression cylinder is very evident:

Have you checked engine vacuum with a simple vacuum gauge? I’m betting you going to not have a steady needle it’ll be bouncing rapidly

I have attached results for compression testing. All 3 are included: Static, idle, and snap. They seem alot lower than everything else that I have been looking up on here and everywhere else.

Vacuum guage is not bouncing when the car is on and idling. It is holding at a constant 18hg.

I've spent way to much time on this car so I will likely drop this one off at the dealership tomorrow so I can continue working on all the other cars piling up here at the shop. I'll come back on here if they do figure out the issue. Thanks for everyone's response to this post.

Ricardo_Lira wrote:

. They seem alot lower than everything else that I have been looking up on here and everywhere else.

Vacuum guage is not bouncing when the car is on and idling. It is holding at a constant 18hg.

What is your altitude?

Altitude here in Fresno, CA is 308'

Did you look at the camshaft lobes for that cylinder?

**UPDATE**FIXED**

Just to make sure I don't leave this thread unanswered, the problem haa been fixed. After taking the car to the dealer, they told me the issue was the cylinder head and quoted me $3700. I went back to the machine shop that worked on the cylinder head. They were really upset with me because I took the car to the dealership and pretty much told me to to get lost(They told me alot more than get lost). I won't be using them anymore. I went ahead and purchased a reman head from the dealer for a bit over $500. I did the head job again and also replaced all the lifters and rocker arms for that cylinder.

Car runs perfect now without any issues. Customer will be picking up the car tomorrow. Thanks for everyone's help.