P0300 random misfire code, at the same time transmission over temp. Please help!!! - JeepForum.com
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Unread 12-02-2013, 06:44 PM   #1
Jam1869
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Join Date: Dec 2013
Location: Charlottesville, Virginia
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P0300 random misfire code, at the same time transmission over temp. Please help!!!

Hi all, the other day my Wk suddenly starting to show an overheating vehicle, and as I turned off "transmission over temp" showed up in my display. Afterwards, I had trouble starting my car, finally getting the engine to turn over after twenty minutes or so. Check engine light signaled a random misfire code (p0300). I immediately changed my spark plugs as they were pretty old, and the problem seemed to be fixed. Lo and behold, three days later the ignition trouble started again. Transmission signal showing up as well. Either it's a huge coincidence or these problems are somehow related. Could someone please help?

Thanks so much in advance for any advice anyone can provide.

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Unread 12-02-2013, 06:57 PM   #2
Walt
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Location: Midland, MI
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Need more info to help.....model year / engine / drivetrain / maintenance status / etc.

Recommend you fill out your profile with this data.
__________________
HEMI CLUB MEMBER #45; SILVER WK CLUB MEMBER #13
'08 WK GC Limited. 5.7L HEMI. Quadra-Trac II. Bright Silver Metallic. Class IV hitch.
Michelin LTX M/S tires. Fumoto oil drain valve. Billet Technology oil catch can.
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Unread 12-02-2013, 08:27 PM   #3
Jam1869
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Quote:
Originally Posted by Walt
Need more info to help.....model year / engine / drivetrain / maintenance status / etc.

Recommend you fill out your profile with this data.
2006 Laredo, 2wd, 3.7L V6, 137k miles, fresh oil change
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Unread 12-03-2013, 04:17 PM   #4
Jam1869
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Update: When I stop and go idle, fluid starts to leak and noise comes from glove box area. Also, cold starts are not an issue.
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Unread 12-03-2013, 07:04 PM   #5
Walt
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Quote:
Originally Posted by Jam1869 View Post
Update: When I stop and go idle, fluid starts to leak and noise comes from glove box area. Also, cold starts are not an issue.
I do not have a 3.7L V-6. However, it sounds like a leaking heater core. Check the leaking fluid to see if it is somewhat slippery, pink, and smells sweet. DO NOT TASTE IT as ethylene glycol is highly poisonous.

You can do a cooling system pressure test to see if there is a pressure boundary breach somewhere. Radiator cap is stamped with the system pressure, so you know the psig to apply. If there is a leak, I would expect that the coolant overflow tank level would be dropping also. Another thing to check.

Likely your coolant is MOPAR HOAT (Hybrid Organic Acid Technology), so care must be taken for a compatible replacement.

When you get through, you might consider a new radiator cap if it over 6 yrs. old. The springs get weak and fail to hold cooling system pressure. Think they run ~$7.

My 2 cents worth. Caution: This advice may be worth what you paid to get it!
__________________
HEMI CLUB MEMBER #45; SILVER WK CLUB MEMBER #13
'08 WK GC Limited. 5.7L HEMI. Quadra-Trac II. Bright Silver Metallic. Class IV hitch.
Michelin LTX M/S tires. Fumoto oil drain valve. Billet Technology oil catch can.
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Unread 12-03-2013, 09:50 PM   #6
Jam1869
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Location: Charlottesville, Virginia
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Quote:
Originally Posted by Walt

I do not have a 3.7L V-6. However, it sounds like a leaking heater core. Check the leaking fluid to see if it is somewhat slippery, pink, and smells sweet. DO NOT TASTE IT as ethylene glycol is highly poisonous.

You can do a cooling system pressure test to see if there is a pressure boundary breach somewhere. Radiator cap is stamped with the system pressure, so you know the psig to apply. If there is a leak, I would expect that the coolant overflow tank level would be dropping also. Another thing to check.

Likely your coolant is MOPAR HOAT (Hybrid Organic Acid Technology), so care must be taken for a compatible replacement.

When you get through, you might consider a new radiator cap if it over 6 yrs. old. The springs get weak and fail to hold cooling system pressure. Think they run ~$7.

My 2 cents worth. Caution: This advice may be worth what you paid to get it!
Thanks for the advice...it's actually green so coolant I'm guessing. Also worthy of noting is that the heater is blowing cold air in my cabin. So we have random misfires, external coolant leak, trouble starting a warm engine, engine getting hot in idle. Gasket?

I may get berated for this, but if I'm planning to only keep this vehicle for another few months, is Stop Leak a viable thing to try as a sort of catch-all?
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Unread 12-04-2013, 03:30 PM   #7
Walt
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2008 WK 
 
Join Date: Oct 2009
Location: Midland, MI
Posts: 1,526
Quote:
Originally Posted by Jam1869 View Post
Thanks for the advice...it's actually green so coolant I'm guessing. Also worthy of noting is that the heater is blowing cold air in my cabin. So we have random misfires, external coolant leak, trouble starting a warm engine, engine getting hot in idle. Gasket?

I may get berated for this, but if I'm planning to only keep this vehicle for another few months, is Stop Leak a viable thing to try as a sort of catch-all?
One of the 3.7L V-6 guys will have to opine on the starting/running issues. Head gasket failure would likely show up as hard starting cold and rough running until it burns off. You would see oil in the coolant and/or water in the lube oil.

Stop leak may work, depending on hole size. Probably fail on first hot day next summer. Try to look in the area of the leak to see if there is a hose connection to tighten or can be wrapped/patched easily.

Blowing cold air sounds like a blend door. However, if the heater core is not full of coolant (for instance, an air bubble from a partially full system), it will not transfer heat effectively. I would touch this symptom until after the cooling system leak is rectified, the coolant system is burped of air, and it holds rated pressure/temperature.
__________________
HEMI CLUB MEMBER #45; SILVER WK CLUB MEMBER #13
'08 WK GC Limited. 5.7L HEMI. Quadra-Trac II. Bright Silver Metallic. Class IV hitch.
Michelin LTX M/S tires. Fumoto oil drain valve. Billet Technology oil catch can.
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Unread 12-04-2013, 04:17 PM   #8
johngreen1234
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2010 WK 
 
Join Date: Nov 2012
Location: beverly hills, ca
Posts: 296
Just to repeat what Walt said, if the coolant is green you have the wrong coolant in there.
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