Intermittent rough engine and misfires both in idle and while driving, codes P0305 and P0300

Tiny
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  • 2007 JEEP COMMANDER
  • 4.7L
  • V8
  • 4WD
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Seems to be worse when it’s hot weather and when lower on fuel. Even worse if running the A/C. Have replaced plugs, coils, alternator, throttle position sensor and MAP sensor. It has definitely got better with all the changes but still not fixed. Did a compression test and came back with around 150 PSI all around. Just did a fuel pressure test and it was about 55 when key on engine off. When I went ahead and started it the pressure was jumping rapidly between 155-165. You can occasionally smell duel at start up as well. The 2 main codes coming up are p0305 and p0300 misfire codes. Not sure if I should look at fuel pump or injectors next. Or something else. Will try and attach a video of the gauge at idle.
Friday, June 26th, 2020 AT 11:14 AM

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Tiny
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I have some ideas on what this could be but we need to address the fuel pressure first. At key on with 55 PSI is just about perfect. However, when you start the vehicle and it jumps 100 PSI does not sound possible. This pump is a low pressure pump so we have to be missing something.

Are you testing this with a gauge or looking at a scan tool? Here is a guide on how we need to do this with a gauge:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If you are using a gauge can we get a video of the gauge when this happens? Next we may need to try another gauge because it may be the issue.
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Friday, June 26th, 2020 AT 11:33 AM
Tiny
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I am so sorry, that was a typo. It is jumping between 55-65.
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Friday, June 26th, 2020 AT 11:37 AM
Tiny
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I think I got the video to upload this time.
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Friday, June 26th, 2020 AT 11:39 AM
Tiny
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Okay. That makes more sense. As for the fluttering, that is not uncommon to flutter a little bit but that seems pretty large.

Let's try monitoring the fuel pressure and rev the engine and see if the gauge stops bouncing when you rev the engine. If it does the fuel pump is failing.

The other possible cause is a leaking injector which would make more sense with the misfire that you are getting.

Lastly, we should monitor live PCM data when the engine is running to see if it is rich. If it is running rich then we can feel better about going after an injector or other fuel issue. This would require a scan tool capable of doing this. Any chance you have one?
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Saturday, June 27th, 2020 AT 6:58 PM
Tiny
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I do have one. Been trying to keep and eye on it without crashing, lol. I took a peak at it when it was doing some sputtering at idle the other day. I’ll post the picture.
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Saturday, June 27th, 2020 AT 7:04 PM
Tiny
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It doesn’t always stay that way, noticed that it will come back around normal range while driving but still goes up and down. Mostly in the positive side as the pic suggests.
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Saturday, June 27th, 2020 AT 7:06 PM
Tiny
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Also the vehicle was driven pretty heavy today. Started off running almost perfect (didn’t run A/C) The more start and stopping I did it would have little sputters when restating big would go away pretty quick. Ended up having to hook up a trailer to it to pick up and drop off a dryer and had the A/C running as well (hot day) The sputtering and hesitations kept getting worse the longer we drove. When restarting and heading back it got rough enough for the CEL to start blinking for a couple seconds and then stopped. Turned off the A/C and drove it back. Had some hesitations and stutters but made it. When parking it stalled on me. Let it cool down for a couple hours and when heading back home (no ac and no trailer) barley had any issues. A Few stutters at the beginning and slower on acceleration but got better as I went. Checked the codes and had p0305, p0300 and now also p0304. Checked the misfire counts on the scanner and had misfires in all the cylinders, at least half were in the teens.
Sorry for the long post but trying to be as specific as possible. Going to go ahead and order the fuel pump while I wait for your reply. Thank you so much for the help.
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Saturday, June 27th, 2020 AT 8:50 PM
Tiny
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We may have an o2 sensor issue as well. You short and long term on bank one are pretty positive. That would indicate to the PCM that there is too much oxygen so it adds more fuel. However, it seems like there is too much fuel already. That means the o2 sensor could be reading it wrong. You can try swapping from side to side and see if the numbers change. If not, then we may have a fuel injector issue on that bank.
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Sunday, June 28th, 2020 AT 8:39 PM
Tiny
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Well, I ordered a fuel pump. What should I be looking for as far as the sensors or injectors go while waiting for it to come in? I can see the sensors oscillating on my scanner while running.
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Monday, June 29th, 2020 AT 8:50 AM
Tiny
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Drove the vehicle today. I’ll post a pic of the fuel trims at startup. While driving I noticed they would go up and down both short term and long term. The long terms would briefly get to mid to upper terms positive then come back down pretty quickly. Seemed to go higher when coming off the gas or braking and also seemed like they were higher when feeling some sputtering.
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Monday, June 29th, 2020 AT 2:22 PM
Tiny
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That sounds pretty normal. The short term fuel trims should be bouncing up and down around 0 and long term should be more consistent and not bounce as much.

I think the sputtering is related to the pressure bouncing so erratically. Let us know what happens after the pump is replaced. Thanks
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Monday, June 29th, 2020 AT 8:20 PM
Tiny
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Okay, so first Happy 4th!

Got the fuel pump swapped last night. It was running pretty rough before the change and after it started up and idled smooth. Felt good driving, no hiccups and acceleration seemed better. Didn’t run the AC at first but did when got closer to home. Didn’t seem to have any issues though it was in the mid 70's out.

Got home, stopped and restarted. I let it idle for at least 20 minutes. It did good at first then would start getting smaller sputters but not as bad as before and not as frequent. I’ll see how it does when it’s hotter out.

I plugged my scanner in to look at fuel trims at idle. I’ll post the pics but my long terms were +13.3 and +9.4 and stayed at those numbers pretty much the whole time. I would give it gas and they would move a little and immediately go back to those numbers.

I also went in the test part of the scanner to see misfire counts and went in the O2 heater monitor test. This is after it was idling for a bit. B1S1 was at 77 F which was outside temp. B1S2 was 95F. B2S1 was 113F and B2S2 was 59F. Not sure if that’s even important but found it strange the temps would be so different. The live data always shows both my Cat converters at the same temperature.

I also noticed that my thermometer in the car was reading 76F but my ambient temperature sensor on the scanner was reading 115F. Are these supposed the same?
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Saturday, July 4th, 2020 AT 6:46 AM
Tiny
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Happy 4th as well.

The sensor could be an issue but let's do as you suggested first. Let's let it run for a little bit and see how it does because those long term fuel trims should begin to change. What were the short term trims? On a properly running engine they will go negative and positive. Kind of bounce around 0 as the engine runs.

Also, does your scan tool have the ability to reset the adaptive numerator? This will reset the long term fuel trim so the PCM will run the engine based off of current numbers vs old numbers. That may be why you are getting the stumble because it is still running off the lean exhaust numbers so it is dumping more fuel causing the stumble when it doesn't really need the fuel now because the pump is supplying the proper amount of fuel now.

Let me know and we can go from there. Thanks
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Sunday, July 5th, 2020 AT 8:10 AM
Tiny
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The short term at that time were -7.0 on B1 and -5.5 on B2. They would fluctuate as I gave gas in idle and the long term numbers would drop as well but immediately go back to the same numbers as before when letting off the gas. I do not believe my scanner has the ability to reset adaptive numerator. Not sure what it is honestly. How can that be done?
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Sunday, July 5th, 2020 AT 8:18 AM
Tiny
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The adaptive numerator is the long and short fuel trims. It is how it is calculated and resetting it, will basically wipe its memory. This adaptive so it will adjust the fuel trims over time but it is not immediate.

I believe you have what is called a GPEC controller on that vehicle which means this process may work to reset it.

Disconnect the battery positive terminal and touch the positive terminal to the negative battery post. This is called a capacitive discharge. Basically that means it depletes the keep alive memory the PCM so that it forgets all its learned data like the adaptives.

If this doesn't work then it is okay. Just drive the vehicle and it will bring those numbers closer to 0.

As for short term fuel trims, that makes sense that they are slightly negative and that is because the long term are positive. It is basically trying to bring those down.

Long story short, I think you fixed it and it will run better as those numbers are relearned.
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Sunday, July 5th, 2020 AT 8:29 AM
Tiny
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I’ll keep you posted. Thank you for your help.
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Sunday, July 5th, 2020 AT 8:37 AM
Tiny
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Sounds great. Thanks. We will wait to hear back.
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Sunday, July 5th, 2020 AT 8:05 PM
Tiny
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Okay, so drove it around today. Really hot day so running A/C. At first no issues at all start and stopped about 3 times. Soon as I got it on the highway you can feel a few stumbles. After about 10 miles and getting back into stop and go and then parking and keeping it running I am getting the sputtering again. Not as bad as before and seems to kind of go away when I turn off the A/C. Ran the scanner and have pending p0305 and p0300 again. Not sure where to go next.

Just got back, had quite a few big stumbles and had my scanner running, the short term trims on both banks would jump up to +20’s and +30’s while it’s happening. They are also jumping up almost as high while it’s sputtering in idle. I did notice the long term was moving up and down like a short term trims while giving it gas or driving. Thought the long terms are supposed to be slow moving. CEL is back on for p0300.
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Monday, July 6th, 2020 AT 2:40 PM
Tiny
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Okay. We need to run through this complete testing for number 5 misfire. We need to suspect an issue with the base engine. Number 9 of this testing is where we need to make sure we cross all these off the list. I suspect a vacuum issue so if you have a vacuum gauge, we need to make sure the needle stays steady. Due to the fuel gauge jumping, we may have a valve spring issue which will show up on a vacuum gauge as well if it is the intake valve.

Take a look at this testing and let me know what you find. However, we are looking for something causing that cylinder to go lean so that is increased oxygen or decreased fuel. Valve spring not sealing would make sense.

We may just want to run a compression check on number 5 and compare it with a couple other cylinders.

https://www.2carpros.com/articles/how-to-test-engine-compression
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Tuesday, July 7th, 2020 AT 6:57 PM
Tiny
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Compression test has been done. Right around 150 psi all around.
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Tuesday, July 7th, 2020 AT 7:16 PM

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