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Discussion Starter #1
I am having a P0300 nightmare.

A little background, My wife started to notice a faint gas smell about four days ago, during any drive in the Commander. The engine was running fine and there was not MIL light. I do have an unrelated TPMS light due to the front right sensor being dead.

After dropping my son off at school yesterday, I was driving about 50 down the road, let off the gas to brake for a stop light. As I was coasting to a stop, I began to feel a rather violent shake and the car stalled. I then restarted and made my way home with few hundred extra RPM and a lot of shaking. As I turned in the drive way the MIL light came on. Broke out the Torque and read the P0300 code.

According to research here:
I followed the following:


P0300 Diagnostic Code - Random Misfire

What does that mean?

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.
A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

Symptoms

Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present
Causes

A code P0300 may mean that one or more of the following has happened:
Faulty spark plugs or wires------Changed all plugs, good gaps
Faulty coil (pack)-----Replaced all coils
Faulty oxygen sensor(s)-----Installed new in 2011 while replacing the cats
Faulty fuel injector(s)----swapped a few around but did not notice any change.
Burned exhaust valve
Faulty catalytic converter(s)----as stated earlier this is new as of 2011
Stuck/blocked EGR valve / passages----Replaced EGR valve and gaskets.
Faulty camshaft position sensor
Defective computer
Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.


Any additional help would be appreciated. Otherwise I am going to be taking it to the dealer for one big repair.
 

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Discussion Starter #2
Oh I also did the SeaFoam application to both the fuel tank and the Intake Manifold.

Ron
 

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You didn't tell us what engine or how many miles on it.

To prevent damage from unburned fuel being dumped into exhaust, the PCM will shut off fuel to cylinders that it detects misfires for, that can cause a "miss" from a minor problem in the ignition to feel like a huge problem as you run only a couple of cylinders for a few seconds.
Faulty spark plugs or wires------Changed all plugs, good gaps
Faulty coil (pack)-----Replaced all coils
Do you have any other codes? i.e. a lot of the possible causes you mentioned would trip other codes as well, so a combination of codes can help you narrow this down.

You've replaced the spark plugs, what about the ignition cables/wires? Does you engine even have ignition cables/wires, some Commander Engines do, some don't. The 3.7L V6 has all coils on top plugs in the earlier years and switched to only one bank having coils and the ignition cables/wires running to the other bank in later years. They do degrade and go bad. At the very least you should check their resistance and make sure they are under the acceptable ohms/foot spec for you engine/vehicle. How about the boots on the coils? Did the new coils come with new boots or did you reuse the old boots on the new coils?

When you replaced the plugs and coils, did you thoroughly inspect and clean all the old ignition parts? To include cleaning the electrical connectors on both sides (Coil and Wire Harness) with electrical cleaner and then seal the connectors with dielectric grease?

I had the same with my Commander, I replaced the plugs (but they no where near the mileage of needing changed), probably unnecessary, and I'm sure what cured it, was thoroughly cleaning all the electrical connections.

I had the Random Misfire codes on a Chrysler MiniVan and nothing was fixing it either. Multiple times I removed and cleaned the wires and all the connections, only when I took the coil pack out (the 3.3L V6 has a single coil pack for the whole motor) did I find Carbon Tracks on it. I had to take it out twice and clean it thoroughly to get the carbon tracks off and stop the misfires, I probably should have replaced it (and the advice is often to just replace any part with carbon tracks, it burns into the case and you really can't clean it off). But I got it working well again.

For my Mini-van it was winter road salt that got up in the ignition and shorted things out. Once I got it cleaned up, and the resulting carbon tracks from it, the problem went away. For my Commander, I had just douched out the motor from working on the thermostat (I got anti-freeze all over it). I clearly must have gotten water into one of the connectors (dirt or road salt will do the same) that caused the ignition problems, I probably pulled the coil and replaced the plugs for no benefit, I probably just had to pull all the connectors and use electrical cleaner on them.

Oh, Catalytic Converters, you should get a code if they have gone bad. The only way for a Cat to cause stalling and rough running is if they clogged, and if it clogged this would NOT be an intermittent problem. I would look other places other than CAT and if the only code is misfires, I would be concentrating on the ignition first.
 

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Faulty oxygen sensor(s)-----Installed new in 2011 while replacing the cats

What manufacturer? It is 2015 now. That was nearly four years ago. I would not rule this out yet.

Faulty camshaft position sensor would be something that I would look at as well.
 

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Discussion Starter #5
Sorry I didn't post the info on the engine.

It is a 2008 5.7L with 150000 miles on it. No other codes. and no spark plug wires, just the engine harness.

I ended up taking it to the dealership, where they pulled the heads and discovered bad exhaust valve on the number one cylinder and likely bad head gasket on the number six cylinder. I am currently down $1400 and they are recommending replacing the head on the left side.

Thanks for the help, but now I only pray that the repair will cost less than the resale value. :grim:
 

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Discussion Starter #6
Update on the 0300 Random Misfire

The Dealership (Orange Park Dodge,Jeep, Ram) replaced the left head and all the consumables. The right head checked out fine, and a new gasket was installed. After putting it all back together the Commander is back to 100% Health and I have put about 50 miles on it with no further problems. Total damage was $3400.00

While I do believe the labor is on the high side, they did do a good job on this one.
 

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Sorry I didn't post the info on the engine.

It is a 2008 5.7L with 150000 miles on it. No other codes. and no spark plug wires, just the engine harness.

I ended up taking it to the dealership, where they pulled the heads and discovered bad exhaust valve on the number one cylinder and likely bad head gasket on the number six cylinder. I am currently down $1400 and they are recommending replacing the head on the left side.

Thanks for the help, but now I only pray that the repair will cost less than the resale value. :grim:
Damn, valve seat failure? These scare me.
 

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I'm glad I stumbled on this post. I've only owned my Jeep for about 3 months and yesterday, my "check engine light" came on for the first time since I bought my XK.

I just did the code check via the key dance and it shows code # P0302, so according to what's posted, I'm getting a misfire in cylinder #2.

I was planning on swapping plugs this month since my 07 Hemi has less then 500 miles till hitting 100k on the odometer. I'm guessing the plugs are long overdue, so hopefully worn out plugs are the only cause.

I am having a P0300 nightmare.

A little background, My wife started to notice a faint gas smell about four days ago, during any drive in the Commander. The engine was running fine and there was not MIL light. I do have an unrelated TPMS light due to the front right sensor being dead.

After dropping my son off at school yesterday, I was driving about 50 down the road, let off the gas to brake for a stop light. As I was coasting to a stop, I began to feel a rather violent shake and the car stalled. I then restarted and made my way home with few hundred extra RPM and a lot of shaking. As I turned in the drive way the MIL light came on. Broke out the Torque and read the P0300 code.

According to research here:
I followed the following:


P0300 Diagnostic Code - Random Misfire

What does that mean?

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.
A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

Symptoms

Symptoms may include:
the engine may be harder to start
the engine may stumble / stumble, and/or hesitate
other symptoms may also be present
Causes

A code P0300 may mean that one or more of the following has happened:
Faulty spark plugs or wires------Changed all plugs, good gaps
Faulty coil (pack)-----Replaced all coils
Faulty oxygen sensor(s)-----Installed new in 2011 while replacing the cats
Faulty fuel injector(s)----swapped a few around but did not notice any change.
Burned exhaust valve
Faulty catalytic converter(s)----as stated earlier this is new as of 2011
Stuck/blocked EGR valve / passages----Replaced EGR valve and gaskets.
Faulty camshaft position sensor
Defective computer
Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.


Any additional help would be appreciated. Otherwise I am going to be taking it to the dealer for one big repair.
 

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I'm glad I stumbled on this post. I've only owned my Jeep for about 3 months and yesterday, my "check engine light" came on for the first time since I bought my XK.

I just did the code check via the key dance and it shows code # P0302, so according to what's posted, I'm getting a misfire in cylinder #2.

I was planning on swapping plugs this month since my 07 Hemi has less then 500 miles till hitting 100k on the odometer. I'm guessing the plugs are long overdue, so hopefully worn out plugs are the only cause.
Almost definitely the case.

I got p0300, p0302,p0303,p0304 or something like that. Plugs were ooold.
 

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I'm feeling pretty good about the case of the issue...no ones screaming dropped valve, plus its running far too smooth.

I just posted here on another thread about how I made an appointment for next week, to have the spark plugs changed. I hate the idea of paying $305 plus tax for something like a plug change. I contemplated doing it myself but having a fused spine can really be a pain at times.

The check engine light on the dash went out today, so I'll look through the threads to learn how to clear the code before going to the dealership. At least that way, I won't have to pay the dealership for that too. I'm sure they won't to any complimentary sorta work.
 

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The PCM has rules about when it will set a Check Engine Light (CEL) and when it will clear it. For most things, the PCM can sense a fault with 100% confidence, like a sensor has an open circuit, so it lights it right away and will turn the CEL off the moment it can tell its fixed. Other things, like misfires, it might let a few misfires happen, cause they can happen with a perfectly good motor from time to time, but more than a certain number within a certain time, it will light the CEL, if the motor goes a certain amount of time without more misfiring's occurring, it will turn out the CEL.

The CEL is lit by presence of stored fault codes, if you clear the fault codes out of volatile memory, the CEL will go out. A way to clear the volatile memory, a.k.a. reseting the PCM is to secure electric power to it and it will dump its memory. The PCM has capacitors in it so it keeps the stored codes, so when you secure the electric power you have to do it a good 30 minutes or more. You can disconnect the battery or pull the fuse that supplies power to the PCM. I've heard if you turn the ignition key like you're going to start the motor, while the PCM has no power, that will drain the capacitors faster and erase the memory right away and you don't have to wait 20-30 minutes.

Some of the better OBDII scanner can clear stored fault codes, which clears the CEL. But without correcting the problem, the PCM will still just set the fault codes again and light the CEL again. And like I said before, for some faults, the PCM sets the code and CEL immediately when noticing it and its constant. So folks have tried to clear a CEL and it just comes back immediately.

Finally, keep in mind OBDII requires the PCM to run self tests on the vehicles engine and emissions and set a code/light a CEL when it fails one of the self-tests. So you can clear codes and go a while before the self test is run again, without having a CEL on, but eventually it will come back when it performs the self-test again and fails.

But, before you say, Wow, now I can pass my state emission test even though a CEL is on, wait, it doesn't work that way. The PCM will also report its status as whether all the emission tests being complete or NOT, so if you reset a PCM to get rid of the CEL to run over to the emission inspection before the CEL comes back on, they'll first check and see the PCM hasn't completed all the self-tests and will turn you away to come back when it does complete the tests.
 

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I just posted here on another thread about how I made an appointment for next week, to have the spark plugs changed. I hate the idea of paying $305 plus tax for something like a plug change. I contemplated doing it myself but having a fused spine can really be a pain at times.
You don't have to go to the dealership to have plugs changed, any independent shop can do it easily and likely charge less than the stealership.

Those with Hemi's report it takes several hours to do the spark plugs, NOT sure why? Sure there are 16 of them. I think some of them might be platinum, which raises the cost of the plugs and you need a lot of them.
 

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You don't have to go to the dealership to have plugs changed, any independent shop can do it easily and likely charge less than the stealership.

Those with Hemi's report it takes several hours to do the spark plugs, NOT sure why? Sure there are 16 of them. I think some of them might be platinum, which raises the cost of the plugs and you need a lot of them.
They are all copper. I think some are just hard to get at. Dealer is probably charging ~2-2.5 hours + materials.
 

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Lots of info there :)
The guy at the service department told me that the dealership's service department averages 2.5 hours to swap the Hemi plugs. He said sometimes they can do it a little faster but sometimes it runs over so they now do a flat rate when they swap Hemi plugs.

When I asked him which plugs they use, he said that they only use the Champion copper plugs, that were used OEM from the factory.

I still might call one or two more dealerships and see if anyone can do better then $305. I wish I could trust a local garage to do the work correctly. I'd rather pay $65 an hour where I used to go, before I bough my Jeep but noticed when it comes to certain things, I can tell the mechanics are not well trained.

I had my normal general (non-dealership) garage install TPMS sensors in 4 tires and after over 1.5 hours they gave up on getting the tire pressure sensors to read on the computer and were convinced I provided them with the wrong sensors or something. Fortunately, they only charged me $75 because they couldn't fix them correctly. I went home and learned how to do it online, had the computer learn the positions and fixed everything in 15 min.

So, some things I'm ok with at the general garage...but I worry that they don't know to (or wont) torque the plugs properly or will fail to properly gap them. I think the Chrysler dealership will be used to working on these and hopefully make less mistakes.

Of course the trade off is that the plugs are like $70 for 16 and labor comes out to about $94 per hour.
 

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I can't imagine how it would take 2 1/2 hours to change plugs on a Hemi. The plugs are very accessible on the Hemi as compared to many other V8 engines. When I changed mine I don't think it took longer than about 45 minutes. Even with 16 plugs it was a breeze.

Dan
 

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I totally agree with you.

The car I used to take to my mechanic was a late 80s sedan, but I pretty much did everything myself, oil changes, head gasket replacement, replace exhausts...everything really except mounting tires.

I'm just afraid to gamble with their ability to work on newer stuff.

I trust my local guys, always or I would not deal with them.
 
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