08 4.7 Gr Cherokee P0300

  • Elle
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1 week 16 hours ago #201876 by Elle
08 4.7 Gr Cherokee P0300 was created by Elle
I have an 09 Gr Cherokee with a 4.7, with about 78k miles on it. Both sets of plugs (upper and lower) were changed with same brand and part number that was in it before.
About 100 miles later, car began to miss, check engine light flashing. Code P0300 was a pending code.
Over the course of the last week I have:
Put original plugs back in
Swapped coils
Swapped boots
Swapped wires
Swapped injectors
Compression tested all 8 and they are all almost identical
When at idle, at first start up, I can watch cylinders #1 and #3 misfire, then stop misfiring when idle evens out. If gas pedal depressed/engine revved, misfires come back. They also come back under load
I have just removed the intake manifold to check gasket and to see better into the cylinder.
Going to put new gasket in, but I'm at a loss at what to do next

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1 week 7 hours ago #201880 by relative4
Replied by relative4 on topic 08 4.7 Gr Cherokee P0300
Regarding the swap meet bonanza, exactly how did you swap? Did you swap the above components between say cylinder 1 and cylinder 2? What boots and wires are you referring to?
If the intake manifold gasket doesn't fix it, can you post your fuel trims at idle, 2500, and 4000?

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  • ToyotaKarl
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1 week 6 hours ago - 1 week 6 hours ago #201882 by ToyotaKarl
Replied by ToyotaKarl on topic 08 4.7 Gr Cherokee P0300
Those 4.7's were well known for head/valve seat issues (Intake valve seats coming out), valve springs breaking and cracking in the heads.

I would do a leak down test on those problem cylinders...

Good luck!

-Karl

Give a man a fish and he will eat for a day. Teach a man to fish and he will sit in a boat all day drinking beer.

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Last edit: 1 week 6 hours ago by ToyotaKarl.

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