08 4.7 Gr Cherokee P0300

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2 months 1 week 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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2 months 1 week 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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2 months 1 week ago - 2 months 1 week 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

Just because it is legal, doesn't make it right....

ASE Certified Master Tech
Last edit: 2 months 1 week ago by ToyotaKarl.
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2 months 3 days ago #202001 by Elle
Replied by Elle on topic 08 4.7 Gr Cherokee P0300
STFT doesn't get interesting until 2000 and 2500, not sure if the names of these attachments come through

below is 2500


below is idle


below is 2500
Attachments:

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2 months 3 days ago #202002 by Elle
Replied by Elle on topic 08 4.7 Gr Cherokee P0300
Swapped each component separately to see if the misfires followed the component or remained in the cylinder.

New intake manifold gasket and injector o rings are in and complete same issue

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2 months 3 days ago #202003 by Elle
Replied by Elle on topic 08 4.7 Gr Cherokee P0300
Will do leak down test next, thanks

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4 weeks 1 day ago #202338 by Elle
Replied by Elle on topic 08 4.7 Gr Cherokee P0300
In the rare chance that someone else has this issue, I resolved it by relearning cam and crank sensors.

Thank you so much for all of you that brainstormed and offered tips and help!!

It gave me a reason to order my o ring kit for leak down tester and for this stupid scan tool to earn what I stupidly paid for it years ago!

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