In-depth look into p0300

[Steel MPG Saver]

Have you replaced your MAF? Sounds like it is not reading the slower airflow correctly at idle after the engine warms up and switches to closed loop from open loop. The MAF controls fueling when warm, so if you can tune the PCM, maybe add 5% to the lower MAF tables?

 

[MP9C]

I have not changed it, might be something to look into.

 

[Steel MPG Saver]

Do you run a dry filter or an oiled K&N style? Could be the oil from the filter affecting the MAF. I would replace rather than clean the MAF, the electrodes are very sensitive.

 

[MP9C]

The truck still has the factory intake.

 

[RedSRT4Me]

There is no MAF.

Modern mopars are all speed density using a map sensor.

 

[Mister Luck]

There is no MAF.

Modern mopars are all speed density using a map sensor.

I believe that started after 2001 I didn’t see it until 2004

 

[Donjuan2002]

Any update? I’m having the same exact issues on my 2009 Hemi. I bought this truck used with this known issue. I’ve been wanting a 5.7 dodge for a while so this one was relatively affordable given the present issue and the fact that I can do any type of engine repair if needed since this is mainly my hobby.

-P0300
-Misfire on 4 and 6 (a few on 2) only at idle based on mode 6 misfire counters.
-No tick noise
-has at least 2 cracked bolts on each exhaust manifold(I don’t think this is contributing to the misfires, but I could be wrong).
-Already swapped coils and injectors from numbers 1, 3, 5, and 7(no misfires on these cylinders). No change. Same results.
- installed new spark plugs. No change.
- when it first starts up, I disconnect coils and RPMs drop an all individual cylinders so they are all firing during this time before ECM shuts down 4 and 6 due to high misfire counts at idle.
-after idling for about 1 minute CEL turns on and cylinders 4 and 6 stop firing. Engine vibration becomes more apparent at that point since ECM shuts those cylinders due to high misfire counts.
-As engine warms up, the misfire counter slows at idle and doesn’t throw the CEL. However, it’s still misfiring on 4,6, and 2, but at a slower rate. Engine still shakes and vibrates slightly during this time.
-Engine has full power during acceleration otherwise and no misfire felt during acceleration.
-Noid light tested injector harnesses and they all work until ECM shuts them down, which is normal.
-If I keep RPMs above 1200, misfires almost disappear according to misfire counters.
-oil pressure is around 50 psi according to computer although I have not physically confirmed it with a mechanical pressure gauge.
-Lifted valve cover and all valves opening normally as I turn the engine.
-No broken valve springs or other valve train problems observed.
- replaced ECM with latest Firmware and made no difference.
-compression test are all 195-190 psi on 2,4, and 8. Number 6 shows 160 psi. This is the only thing that worries me.
- sprayed carb cleaner around intake to check for vacuum leaks and no change.
-swapped camshaft sensor. No change.


Things to do:
-swap crank position sensor for the heck of it since it’s relatively inexpensive.
- relearn crank position sensor and camshaft position sensor with Xtool D7 diagnostics scanner. Just figured out how to do this.
-do leak down test
-check fuel pressure(how do I do this? There is no fuel pressure port)
-check vacuum
- physical oil pressure check.
-fix broken exhaust manifold bolts.

Pending my above to do list doesn’t give me any more useful information I’m pretty much ready to pull engine and check camshaft/lifters. Plus the fact that I have one cylinder showing 160 psi(number 6), which also has the most misfires at idle. I’m hopeful the leak down test on number 6 will give me more insight as to what is going on. Perhaps I have a valve not fully seating on cylinder 6. Could this cause misfires on 4 and 2? Note that the misfires on number 2 are much less than number 4, which are slightly less than number 6, which has the most misfires.

Any other suggestions?

 

[MP9C]

I still have not opened up my engine, after flashing my pcm with a 800 rpm parameter 95% of my issues went away. At this point I would say it’s a sticking lifter in my situation.

Its possible you could have the same issue, I would suggest doing a wet compression test on 6 to see if your pressure goes up, If it does it’s not a valve issue. If it doesn’t it’s a valve or seat.

 

[Hemi395]

I have my truck set at 700rpm on my current homemade tune and the difference in idle oil psi is about 15psi. The factory tune has it set at 500 which is way too slow IMO.

 

[Sherman Bird]

Any update? I’m having the same exact issues on my 2009 Hemi. I bought this truck used with this known issue. I’ve been wanting a 5.7 dodge for a while so this one was relatively affordable given the present issue and the fact that I can do any type of engine repair if needed since this is mainly my hobby.

-P0300
-Misfire on 4 and 6 (a few on 2) only at idle based on mode 6 misfire counters.
-No tick noise
-has at least 2 cracked bolts on each exhaust manifold(I don’t think this is contributing to the misfires, but I could be wrong).
-Already swapped coils and injectors from numbers 1, 3, 5, and 7(no misfires on these cylinders). No change. Same results.
- installed new spark plugs. No change.
- when it first starts up, I disconnect coils and RPMs drop an all individual cylinders so they are all firing during this time before ECM shuts down 4 and 6 due to high misfire counts at idle.
-after idling for about 1 minute CEL turns on and cylinders 4 and 6 stop firing. Engine vibration becomes more apparent at that point since ECM shuts those cylinders due to high misfire counts.
-As engine warms up, the misfire counter slows at idle and doesn’t throw the CEL. However, it’s still misfiring on 4,6, and 2, but at a slower rate. Engine still shakes and vibrates slightly during this time.
-Engine has full power during acceleration otherwise and no misfire felt during acceleration.
-Noid light tested injector harnesses and they all work until ECM shuts them down, which is normal.
-If I keep RPMs above 1200, misfires almost disappear according to misfire counters.
-oil pressure is around 50 psi according to computer although I have not physically confirmed it with a mechanical pressure gauge.
-Lifted valve cover and all valves opening normally as I turn the engine.
-No broken valve springs or other valve train problems observed.
- replaced ECM with latest Firmware and made no difference.
-compression test are all 195-190 psi on 2,4, and 8. Number 6 shows 160 psi. This is the only thing that worries me.
- sprayed carb cleaner around intake to check for vacuum leaks and no change.
-swapped camshaft sensor. No change.


Things to do:
-swap crank position sensor for the heck of it since it’s relatively inexpensive.
- relearn crank position sensor and camshaft position sensor with Xtool D7 diagnostics scanner. Just figured out how to do this.
-do leak down test
-check fuel pressure(how do I do this? There is no fuel pressure port)
-check vacuum
- physical oil pressure check.
-fix broken exhaust manifold bolts.

Pending my above to do list doesn’t give me any more useful information I’m pretty much ready to pull engine and check camshaft/lifters. Plus the fact that I have one cylinder showing 160 psi(number 6), which also has the most misfires at idle. I’m hopeful the leak down test on number 6 will give me more insight as to what is going on. Perhaps I have a valve not fully seating on cylinder 6. Could this cause misfires on 4 and 2? Note that the misfires on number 2 are much less than number 4, which are slightly less than number 6, which has the most misfires.

Any other suggestions?

Do the Zulu Warrior dance, incantations might help as well! Just Kidding! LOL. I'd recommend you look at mode 6 data with a good scanner and someone competent enough to narrow it down. I recently had a 99 Tahoe with a broken weld on the passenger side catalytic converter causing a rattle which set of P0300! A quickie spot weld fixed it!

 

[Xsen]

Kind of reviving this thread I guess. Got this issue the day before, cleared the code, but it came back today.

Planning to do a test drive with the scanner to see exact misfire conditions. I know I have one or two exhaust manifold studs broken on the second bank. No tick when engine is warm, 0w40 oil with Ceratec additive.

OP, have you ever found out the cause in your case?

EDIT: took a drive with the scanner on. Misfiers happen under heavier-than-average load on both banks, worst on cylinder 1 (334), bad on cyl 5 (218), also cyl 4 (85) and cyl 8 (60). Idling & cruising shows no misfires at all.

Going to swap the spark plugs, if the problem persists - swap the coil, then move on to the valvetrain. No audible ticking on the warm engine.

 

[Donjuan2002]

Any update? I’m having the same exact issues on my 2009 Hemi. I bought this truck used with this known issue. I’ve been wanting a 5.7 dodge for a while so this one was relatively affordable given the present issue and the fact that I can do any type of engine repair if needed since this is mainly my hobby.

-P0300
-Misfire on 4 and 6 (a few on 2) only at idle based on mode 6 misfire counters.
-No tick noise
-has at least 2 cracked bolts on each exhaust manifold(I don’t think this is contributing to the misfires, but I could be wrong).
-Already swapped coils and injectors from numbers 1, 3, 5, and 7(no misfires on these cylinders). No change. Same results.
- installed new spark plugs. No change.
- when it first starts up, I disconnect coils and RPMs drop an all individual cylinders so they are all firing during this time before ECM shuts down 4 and 6 due to high misfire counts at idle.
-after idling for about 1 minute CEL turns on and cylinders 4 and 6 stop firing. Engine vibration becomes more apparent at that point since ECM shuts those cylinders due to high misfire counts.
-As engine warms up, the misfire counter slows at idle and doesn’t throw the CEL. However, it’s still misfiring on 4,6, and 2, but at a slower rate. Engine still shakes and vibrates slightly during this time.
-Engine has full power during acceleration otherwise and no misfire felt during acceleration.
-Noid light tested injector harnesses and they all work until ECM shuts them down, which is normal.
-If I keep RPMs above 1200, misfires almost disappear according to misfire counters.
-oil pressure is around 50 psi according to computer although I have not physically confirmed it with a mechanical pressure gauge.
-Lifted valve cover and all valves opening normally as I turn the engine.
-No broken valve springs or other valve train problems observed.
- replaced ECM with latest Firmware and made no difference.
-compression test are all 195-190 psi on 2,4, and 8. Number 6 shows 160 psi. This is the only thing that worries me.
- sprayed carb cleaner around intake to check for vacuum leaks and no change.
-swapped camshaft sensor. No change.


Things to do:
-swap crank position sensor for the heck of it since it’s relatively inexpensive.
- relearn crank position sensor and camshaft position sensor with Xtool D7 diagnostics scanner. Just figured out how to do this.
-do leak down test
-check fuel pressure(how do I do this? There is no fuel pressure port)
-check vacuum
- physical oil pressure check.
-fix broken exhaust manifold bolts.

Pending my above to do list doesn’t give me any more useful information I’m pretty much ready to pull engine and check camshaft/lifters. Plus the fact that I have one cylinder showing 160 psi(number 6), which also has the most misfires at idle. I’m hopeful the leak down test on number 6 will give me more insight as to what is going on. Perhaps I have a valve not fully seating on cylinder 6. Could this cause misfires on 4 and 2? Note that the misfires on number 2 are much less than number 4, which are slightly less than number 6, which has the most misfires.

Any other suggestions?

I figured I would update this in case it helps future members.

After doing a leak down test, cylinders 4 and 6 showed excessive leakage.

I went ahead and pulled the engine. I ended up finding lots of issues.

1. I found that the cylinders in 4 and 6 were scratched and the rings were worn.

2. Previous owner must have repaired the right side of the engine as I found that it had new aftermarket non-MDS lifters installed on the right side only. It still had the factory MDS lifters on the left side. No wonder it ran awful when MDS kicked in…

3. Cylinder #2 had a fuel injector that would start misfiring after engine was running for 2-3 minutes.

4. Cam and factory lifters on the left side had begun the infamous lifter/cam failure behavior. Luckily, the cam and lifters were just at the beginning stages and no major damage happened.


All of these issues contributed to my misfire. I decided to go ahead a do a full rebuild on the engine myself at home and installed new cam and OEM lifters. I also replaced the bad injector as well as repaired 5 broken bolts on the exhaust manifolds. I did flatten the manifold surfaces too as both were warped. Once I did this, the engine ran perfectly and has been running beautifully since.

My advice is to never assume it’s one thing that causing your problems.

 

[Sherman Bird]

I know it’s 4,6 because I can see the livestream data in the pcm and watch the misfire counters.

GO TO MODE6! Read data THERE! DO IT! Look at misfire current and history and THAT will debunk other possible issues, or, reinforce them. Either way, you can REALLY narrow your search by using Mode 6! I do it EVERY day for a living.
There isn't a magic bullet for P0300. I've seen a loose catalytic converter shield turn out to be the culprit on a 99 Tahoe 5.3L, as an example of how enigmatic this DTC can be. I recently had a 4.3 2006 GMC Sierra with 273,000 miles on it in here for a stand alone P0300.

2 Dealers and 4 other shops had thrown many parts at it to the tune of thousands of dollars in "efforts" to fix it.
Mode6 took me to the 2 main culprits which fixed the problem (simple problems). Sadly I had to re-repair many of the other "shotgun efforts" due to sloppy crappy workmanship.

 

[TurboII]

GO TO MODE6! Read data THERE! DO IT! Look at misfire current and history and THAT will debunk other possible issues, or, reinforce them. Either way, you can REALLY narrow your search by using Mode 6! I do it EVERY day for a living.
There isn't a magic bullet for P0300. I've seen a loose catalytic converter shield turn out to be the culprit on a 99 Tahoe 5.3L, as an example of how enigmatic this DTC can be. I recently had a 4.3 2006 GMC Sierra with 273,000 miles on it in here for a stand alone P0300.

2 Dealers and 4 other shops had thrown many parts at it to the tune of thousands of dollars in "efforts" to fix it.
Mode6 took me to the 2 main culprits which fixed the problem (simple problems). Sadly I had to re-repair many of the other "shotgun efforts" due to sloppy crappy workmanship.

Ok, what is "Mode 6" I'm totally new here. I have some mechanical experience. I have 4.7 that has misfires in 7 & 8. I switched the COP between 6 & 8 and the misfire did not follow. I just put new plugs in it and I'm at a loss of what to do next other than pull a valve cover to see if it is mechanical. ANY help would be appreciated. Sorry if I hijacked the thread. I will make a new one of need be.

 

[Hemi395]

In generic OBD2 there's several modes available to look at data. Mode 6 has all your misfire data as well as other data. Unfortunately most code readers aren't able to view Mode 6 unless it explicitly says it does.

 

[Sherman Bird]

In generic OBD2 there's several modes available to look at data. Mode 6 has all your misfire data as well as other data. Unfortunately most code readers aren't able to view Mode 6 unless it explicitly says it does.

Well, folks! If you're going to try to fix it cherself, you're going to have to pony up for a higher end scanner which DOES read mode6 AND has bidirectional controls!

Grandpa always said that you have to have the correct tools to fix something. Socket wrenches, screwdrivers, et.al. no longer suffice what with ADAS, and other sophisticated electronics which belong on a Boeing!

Surely, with all that moola you guys save by doing it yourself, a higher cost scanner is affordable!

Mode6 really shortens my diagnostic time by directing me to the problem with way more data than just a code. It also is a quick elimination process. Codes are the index to what's wrong. Following data PID's is the first step in what's next, then pin point tests.

When one gets lucky by scanning a code and replacing the part that is implicated in the criteria for setting that code AND that fixes the problem, he or she should seriously consider buying several lottery tickets.

 

[TurboII]

Well, folks! If you're going to try to fix it cherself, you're going to have to pony up for a higher end scanner which DOES read mode6 AND has bidirectional controls!

Grandpa always said that you have to have the correct tools to fix something. Socket wrenches, screwdrivers, et.al. no longer suffice what with ADAS, and other sophisticated electronics which belong on a Boeing!

Surely, with all that moola you guys save by doing it yourself, a higher cost scanner is affordable!

Mode6 really shortens my diagnostic time by directing me to the problem with way more data than just a code. It also is a quick elimination process. Codes are the index to what's wrong. Following data PID's is the first step in what's next, then pin point tests.

When one gets lucky by scanning a code and replacing the part that is implicated in the criteria for setting that code, he or she should seriously consider buying several lottery tickets.

I have no problem getting a more sophisticated scanner. The problem I've found doing research on them is everybody has their own opinions of what is "good". I basically just want to be able to diagnose what the problem is. I don't need a $7000 Snapon scanner. If I had money to burn I'd take it to a reputable repair shop (those a few and far between) and let them fix it. I've seen so many people screwed out of money by repair shops it is ridiculousl!

 

[A_mod_too_far]

I have no problem getting a more sophisticated scanner. The problem I've found doing research on them is everybody has their own opinions of what is "good". I basically just want to be able to diagnose what the problem is. I don't need a $7000 Snapon scanner. If I had money to burn I'd take it to a reputable repair shop (those a few and far between) and let them fix it. I've seen so many people screwed out of money by repair shops it is ridiculousl!

Xtool d8 had a positive review by solar garage when he was doing his rebuild series on youtube. Its about 700$ on amazon and can do just about everything. I think Scott rods also bought one if I remeber right.

 

[Hemi395]

I have a Thinkdiag that I use my phone as the interface for. Best value for the money I could find for OEM level functionality.

 

[TurboII]

Xtool d8 had a positive review by solar garage when he was doing his rebuild series on youtube. Its about 700$ on amazon and can do just about everything. I think Scott rods also bought one if I remeber right.

That has WAY more than I would ever need. LOL I did watch a review on xTool's A30 that is a dongle that would do more than I'll ever need as well for a lot less.