Need help 4.7 ho misfire and oil - JeepForum.com
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post #1 of 8 Old 07-24-2021, 01:57 PM Thread Starter
GIJoeZ28
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Need help 4.7 ho misfire and oil

'04 gc overland 4.7h.o. motor was rebuilt 40k ago been driving great. recently had dash light come on for misfire on #7 and I noticed the lose of power too. Anyways I replaced both forward O2 sensors checked to verify cats were not clogged and still does it...I changed the filter regulator still does it...fuel pressure sat. started changing spark plugs #7 looked ok besides obvious that they needed to be changed. #8 has oil all over it, I ran a borescope down cylinder and did not see much. Does look like there was some kind of debris on the cylinder #8 but i cant tell what it is....did a compression check and all cylinders passed. ran my leak down tester and didn't get anything back on that either...did a block test and it passed that too...i did notice the the pcv was pretty gunked up so I'm going to change that...if the pcv gets clogged would it pull oil into #8 being as its closed to where it goes into intake? I'm really stumped on this...atm I see i have two choices....put it back together with new plugs and pcv drive it pull plugs and borescope again to see if oil present or tear intake off clean it possibly pull head off with all new gaskets and verify its not the valve guide. heads were fully rebuilt when the motor was 40k ago.



any advice be great thanks

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post #2 of 8 Old 07-24-2021, 02:01 PM
cDee63
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If your PCV is plugged you will have all kinds of problems like this. That being said my rebuilt heads the drivers side dropped a seat after 12,000 miles so don't rule that out. I replaced it and the other original started puffing oil on start up as well after around 20,000 miles, don't rule that out as well.

2004 Limited, 4.7 modded slightly, IRO 3" RockLink LA front, adjustable SA rear, Bilsteins, Addco bar, JKS disconnects. Coming attractions include 242hd, IRO SYE and Woods DS right after the new engine/trans..
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post #3 of 8 Old 07-24-2021, 09:59 PM
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you did the free stuff, so do the cheapest thing. pcv, and clean out the hoses. i'd be curious about something foreign in a cylinder. try to blow it out, running the engine with that plug removed for a few seconds? if it's ferrous, maybe you have a small magnetic pick-up tool, you can snake into the opening and see if it comes out?

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post #4 of 8 Old 07-25-2021, 10:45 AM
three_jeeps
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Get a new PVC and new plumbing.
Various outlets sell the whole assembly. IIRC, I got mine through amazon 4+ years ago. Search this forum for details.
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post #5 of 8 Old 07-25-2021, 11:59 AM Thread Starter
GIJoeZ28
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Thanks everyone. I am getting a new pvc valve and I will be cleaning the heck out of the rest of it. Do you think i need to pull the intake off and clean inside of that section or just new pvc and clean hoses?
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post #6 of 8 Old 07-25-2021, 12:14 PM Thread Starter
GIJoeZ28
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forgot to mention the debris...hard to tell what it was...but to me it looked more like fiber substance then metal...pushing with camera though it seemed hard...now dont take my words as 100 accurate as it is very hard to tell with the borescope...angle of the cylinder and the small hole i put it threw made it very difficult to maneuver and see anything. I do not feel like it was metal...i did turn over cylinder once or twice doing compression check after and i dont see it in there...hoping it blew out..or its on other side of piston for which the camera cant see. At this point i really dont want to tear it down further unless i have too. So....reassembly and hoping new pcv valve and clean hoses plus new spark plugs fix the problem...i will drive it around block bring it back let it cool and check the cylinder for oil again or if it has any new symptoms then i will know if its fixed for not. I will update yall when i get that done in the next day or two. Thanks for the assist it makes me feel more confident im going the right direction when yall think the same thing i am. Now just to hope this fixes this problem...still need to replace rear axle seal then ill be back on road.
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post #7 of 8 Old 07-29-2021, 08:12 PM Thread Starter
GIJoeZ28
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Problem and solution: Clogged pcv system. Backed up and dumped oil into cylinders and fouled up plugs and O2 sensors...back up and running good. Very slight stuffed when warm..but may still be a little crud...I cleaned hoses out and changed out ocv spark plugs and O2 sensors
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post #8 of 8 Old 07-29-2021, 08:33 PM
cDee63
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Check out my PCV write up, https://www.jeepforum.com/forum/f310...4-7-a-4332243/

2004 Limited, 4.7 modded slightly, IRO 3" RockLink LA front, adjustable SA rear, Bilsteins, Addco bar, JKS disconnects. Coming attractions include 242hd, IRO SYE and Woods DS right after the new engine/trans..
1974 Ironhead Sportster, total custom
High speed, low drag
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