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#4755900 - 05/13/18 12:36 PM 2004 Jeep Loberty 3.7L PO302 Code
tnt31 Offline


Registered: 10/09/05
Posts: 306
Loc: TN
Check engine light just activated Saturday on a 2004 Jeep Liberty 3.7L we bought a couple of months ago. Jeep has 205K miles on it. It appears to be running ok but my wife does indicate a little while prior to the light coming on it did seem to stumble a little bit at idle.

When I first tried scanning it with my Actron CP9410 Pocket Scan Plus code reader I got a link error. Tried again, same result. I then started the engine and got a connection and it shows the PO302 code. (Misfire detected cylinder 2). I then tried to erase the code and the scanner indicates it does erase it but the check engine light stays one and the code reader re-scans and shows the PO302 code. I am guessing it may have something to do with whatever is causing the link error that it does not erase but that is a pure guess. I have tried the scanner on two other vehicles this morning and I do not get the link error.I have visually checked the ODB II port and it appears to look OK.

I guess most important does anyone have experience with these Dodge 3.7Ls and the PO302 codes? Also if any idea why the link error until I actually start the engine and if that is related to why it will not clear? I have the battery disconnected now to see if it will clear the CEL. Leaving it disconnected for 3 to 4 hours.

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#4755905 - 05/13/18 12:45 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
khittner Offline


Registered: 07/13/12
Posts: 344
Loc: Michigan
No experience with a Chrysler 3.7, but did you pull the #2 plug to see what kind of shape it's in? At 12 years and 205K miles, its hopefully not running its OEM plugs, but who knows?

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#4755919 - 05/13/18 12:56 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: khittner]
tnt31 Offline


Registered: 10/09/05
Posts: 306
Loc: TN
Originally Posted By: khittner
No experience with a Chrysler 3.7, but did you pull the #2 plug to see what kind of shape it's in? At 12 years and 205K miles, its hopefully not running its OEM plugs, but who knows?


I have not yet. The person who owned this previously was the original owner and gave us a folder of all maintenance records on the vehicle. Seems like there are invoices for three of four spark plug changes. I will re-check that later.

I looked at where the plugs appear to to be and not sure I have the time to tackle it. Will probably have to take to a local mechanic I use and trust. Would like to hear others experiences if they have had this code with this engine.

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#4755921 - 05/13/18 12:58 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
Chris142 Offline


Registered: 06/05/03
Posts: 17106
Loc: Deplorable in apple valley, ca
Ya plugs first. You do know that you don't need a scanner to pull codes on that jeep?
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#4755926 - 05/13/18 01:11 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
Trav Offline


Registered: 11/20/06
Posts: 19612
Loc: MA, Mittelfranken.de
I don't get it. Whats the point of clearing a misfire code unless its been repaired? Its a hard fault and will come back as soon as the misfire occurs again.
Plugs, coil or injector usually. Start with the plug, check and replace the coil (COP) if defective.
A noid light will tell you you have current going to the injector and at least indicate the ECM driver is okay. You can Ohm the injectors but that wont tell you much other than if was a dead short or open but that's only part of the diagnosis.
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#4755957 - 05/13/18 01:53 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
AVB Offline


Registered: 05/20/12
Posts: 1390
Loc: Georgia
Typically PCM codes can't be cleared on Chryslers with the engine running. I don't know why you are having issues connecting with the KOEO.

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#4756067 - 05/13/18 04:22 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
Highboy Offline


Registered: 04/04/15
Posts: 62
Loc: Saint John,IN
I had a 2002 Liberty and they use copper plugs from the factory. They’re to to changed at 30k miles. Mine where shot at 30k. I would change out the plugs, very easy to do.
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#4756073 - 05/13/18 04:26 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
mk378 Offline


Registered: 09/27/15
Posts: 1486
Loc: USA
If one or more of the plugs is a real bear to R&R, a lot of times that one doesn't get changed even though the receipt says it did.

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#4756152 - 05/13/18 05:53 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
Kage860 Offline


Registered: 04/17/17
Posts: 91
Loc: NY
Yep, I have a Liberty and those copper plugs don't last long. They're actually very easy to change though. I replaced with denso long life iridium 40k ago and have not had any engine issues or codes since. You might want to swap coils with another cylinder to see if the code moves. Maybe run some injector cleaner through the fuel. Hopefully not something expensive to fix.
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2007 Jeep Liberty

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#4756265 - 05/13/18 08:12 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
tnt31 Offline


Registered: 10/09/05
Posts: 306
Loc: TN
Thanks for the replies so far. If the code comes back I will give changing the plugs a try. If that does not fix it then with either change the COP of move the COP to a different cylinder. Rock Auto indicates the OE plug is a NGK V-Power. May try the iridium as kage860 suggest.

Vehicle has an aftermarket Pioneer radio. I have read a few comments that aftermarket radios can at times cause a link error. Still not sure why if the engine is running though it can connect.

Chris142 - I did not know that. Will have to look into it. Thanks

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#4756314 - 05/13/18 08:56 PM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
Kage860 Offline


Registered: 04/17/17
Posts: 91
Loc: NY
The ngk copper plugs are probably the best if you change them often. The ones I got are just quality long life plugs if you only want to do it once. Most people say to stick with the original plugs.
_________________________
2007 Jeep Liberty

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#4756637 - 05/14/18 08:12 AM Re: 2004 Jeep Loberty 3.7L PO302 Code [Re: tnt31]
wag123 Offline


Registered: 06/14/11
Posts: 992
Loc: Texas
Heavy combustion chamber carbon deposits are a common problem on that engine and will cause a misfire. Many people claim that it is caused by the use of E10 gas, but I have doubts about that because E10 should actually burn cleaner.
That engine is also known to have problems with bad valves (and valve springs). Before you blow a bunch of money on it you should do a compression test to find out if you have a bad valve. If you find a bad valve, at 205k miles the Jeep is toast (don't throw good money at it). Reset the CEL and sell it, that is what the previous owner probably did to you.

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