2003 Liberty P0300, the dreaded multiple misfires

[OrangeFish]

2003 Liberty P0300, the dreaded multiple misfires (with a twist!)

Ok gang, I got a weird one on a 2003 Jeep Liberty 3.7 with 160k miles. CEL on, multiple cylinder misfire code (P0300) only, no stuttering, no loss of power, no detonation, no unusual engine noise. I have replaced all spark plugs, all coil packs, PCV valve, and the crank sensor. It's still throwing the CEL and P0300.

The weird thing is the CEL and code appear at 3/4 of a tank and disappear at 1/4 of a tank. So above 3/4 and below 1/4 gas there is no CEL or error code. It has done this with regularity the last 20 tanks or more.

In at a loss, anyone had this happen before, or have any ideas?
:shrug:

 

[uss2defiant]

there's the camshaft sensor as well you could try?

 

[teeje]

Sounds like a bad valve seat. 3.7s are notorious for that. Had that issue before I got my new engine. Try marvel myster oil. It works wonders


2002 Jeep Liberty 3.7L with brand new engine
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[mx3_ryder]

Sounds like a bad valve seat. 3.7s are notorious for that. Had that issue before I got my new engine. Try marvel myster oil. It works wonders


2002 Jeep Liberty 3.7L with brand new engine
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How does marvel mystery do wonders for an already dropped valve seat :ROFLJest:

 

[teeje]

How does marvel mystery do wonders for an already dropped valve seat :ROFLJest:

Did I say "dropped valve seat"? No. I sad BAD valve seat. Carbon deposits amongst other things can cause them not to seal. When the engine is running the valves naturally spin ever so slightly causing intermittent misfires. Research that on whichever search engine you wish, it's a known issue. Please read before posting
Marvel mystery oil cleans the surfaces so they seal better. If you're looking to fix a bad valve seat with marvel mystery oil, well that's a mystery within itself


2002 Jeep Liberty 3.7L with brand new engine
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[southernwake]

What I am curious about is why it is only doing it for 1/2 of a tank. I would think that anything mechanically in the engine would happen all the time not just based on where the fuel level is.

Have you tried running any ethanol free gas through it just to see if after a couple tanks it goes away. The gas level issue and how consistent it is makes me think it is more fuel related at the moment.

Andrew

 

[mx3_ryder]

Did I say "dropped valve seat"? No. I sad BAD valve seat. Carbon deposits amongst other things can cause them not to seal. When the engine is running the valves naturally spin ever so slightly causing intermittent misfires. Research that on whichever search engine you wish, it's a known issue. Please read before posting
Marvel mystery oil cleans the surfaces so they seal better. If you're looking to fix a bad valve seat with marvel mystery oil, well that's a mystery within itself


2002 Jeep Liberty 3.7L with brand new engine
Sent from my iPhone using Tapatalk

You mean if you are looking to fix a "dropped valve seat" with Marvel then that would be mystery in itself. 3.7's are notorious for valve seats loosening and dropping as well if you weren't familiar and throwing rockers. I had a bad misfire on #2 for month or so off and on before finding #2 intake valve seat wedged between cylinder head and valve. I didn't find much of anything googling misfire from carbon deposits just fallen rockers, bad lash adjusters and dropped valve seats and oh yeah, bad coils, spark plugs, ecu etc.

 

[TypeRx]

Funny, just this morning my '03 Jeep Liberty 3.7L threw a P0300, P0302, and P0303. It has 161K miles and is running great. I just changed the oil, air filter, brake fluid, and front rotors this weekend, but doubt any of this is related. I changed the PVC at the last oil change. I haven't changed plugs in 30K+ miles.

Within 30 seconds of the CEL coming on, I ran a scan and cleared the code. Drove for 21 miles to work and everything is A-OK. Hope it was just a fluke, but somehow doubt it....

 

[uss2defiant]

could be bad coils.
I had an intermittent problem like that until I changed the coil

 

[TypeRx]

I ordered new plugs because it is time. My coils are 161k miles old (!) so I will swap those out of the plugs aren't enough


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[JeepUSA]

Hello, I have exactly the same problem for a month now, with the same P0300, P0302, P0303 errors... I've changed all sparks and coils...
Did you still have the issue? Have you already had it fixed, or figured it out what the problem was?

Please, I would very appreciate you could answer to me....I'm a total lost!
Thank you!
Ale

 

[LibertyTC]

I've been down this misfire road. Any engine rattles are signs of: Time to check stem seals/ rockers under the valve covers.
First off a Snap on scanner can be utilized to view the misfires live, and see the counts on which cylinders etc.
Even new coils could be mis behaving, Mopar coil packs recommended.
Even tho the 3.7 is not the smoothest thing on the block, tuning is everything.
Clean the throttle body good & IAC/port too.
Before changing spark plugs, I like to use seafoam poured slowly into intake rear line, at throttle body @ 2000 rpm, and then shut it off for 10 minutes, and then restart it, for a good hwy run once a year. (let the smoke show begin)
Spark plugs: Use the NGK- ZFR6F-11G gap em at .040 inch.
Ethanol fuels like to absorb moisture and fuel can sour a bit after 30 days.
Consider using a good fuel stabilizer like star-tron to fix ethanol related fuel problems and use a higher octane to keep Jeep happy & to blow the dirt out every once in a while!
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The idle should then be smooth and not wavering across rpm range.
Make sure no vacuum leaks and even use a vacuum tester.
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Link: https://www.hemmings.com/magazine/hsx/2012/02/Testing-Engine-Vacuum/3709071.html

 

[Kal-El]

I ordered new plugs because it is time. My coils are 161k miles old (!) so I will swap those out of the plugs aren't enough


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Just curious...what plugs did you go with?

 

[TypeRx]

actually, after clearing the codes, they never reappeared and my Jeep has been running marvelously. 167k miles now!

I do appear to have a small drivers side valve gasket leak so I will change plugs at that time using NGK coppers most likely


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[Kal-El]

actually, after clearing the codes, they never reappeared and my Jeep has been running marvelously. 167k miles now!

I do appear to have a small drivers side valve gasket leak so I will change plugs at that time using NGK coppers most likely

Good idea going with the coppers. They don't last as long as the plat's or iri's, but 3.7's are much happier with 'em. I use the Champions.