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Old 01-18-2010, 07:50 AM   #1
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Blown Valve?

Hey Guys!

I have a '94 4.0L YJ and have been treated to rough idling, loss of power under load, engine shaking and a puttering noise to be technical Changed out the spark plugs with new wires, cleaned the thottle body (lots of oily gunk) With the engine running pulled each plug wire off, the second from the front when pulled off had no change in engine performance, all others made the engine run worse. So is there something wrong with that ones cylinder? Blown valve? O-ring bad? Where do I go from here?

Any help would be well...uhm...helpfull.....
Thank you!

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Old 01-18-2010, 12:10 PM   #2
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Anyone have any ideas to help me out? Could it be a clogged injector?

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Old 01-18-2010, 12:14 PM   #3
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obviously theirs something awry on that cylinder if it was rings it would burn oil like it was going out of style . could be a valve not seating right or an injector or maybe even a hole in the piston. is their any thing else that's wrong with it like excessively bad gas mileage or loosing coolant,ses light anything.
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Old 01-18-2010, 01:27 PM   #4
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I recently replaced the radiator, upper and lower hoses and the water pump. I have not seen any coolant leaks and the engine temp hovers around 200. I have seen some oil leaks around the oil pan gasket. Noise started around the time I put 50/50 coolant in the reserve container, if that helps? If I pull the top off the crank case will I be able to see any possiable damage?
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Old 01-18-2010, 02:57 PM   #5
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Did it run good before you put in new plugs and wire's or did the problem start after you changed them ? If it was after is there a chance that you could of mixed up a couple of wire's ? And first thing you need to do is pull the plug in cyl. 2 and see if it is firing, it could be a bad plug or wire ( they could of been bad new in the box ).
Putting coolant in the tank would not do anything to it. But when it is running is it pushing white smoke out of the tail pipe ? If so that would be a sign of a blown head gasket.
A simple test to find a issue in the heads is by doing a compression test and that will tell you if you have a piston,valve,ring..... problem.

But again pull the plugs and look to see if it is firing.

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Old 01-18-2010, 03:09 PM   #6
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yeah compression test that cylinder and see what u have then u can knock the list down
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Old 01-18-2010, 03:58 PM   #7
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Had the problem before changing the plugs and wires. Rechecked the wires and everyone is in order. I assume the plug and wire to cyl 2 is firing because I got wacked No white smoke from tail pipe. when I do pull the plug on #2 while the engine is running there is no change. How would I go about running a compression test?

Thank you both for any help
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Old 01-18-2010, 04:51 PM   #8
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Did a little research on compression testing and that will be my next step. I'll be back with the results.
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Old 01-20-2010, 06:41 PM   #9
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New Discovery

found a large crack in the exhaust manifold, right where the two pipes converge into the single than run down to the muffler. Could this be the cause of my babies issues? Still have not done the compression test cant get to that until the weekend.
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Old 01-20-2010, 09:26 PM   #10
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No that is the cause of all your problems but since it is cracked and has to be fixed you might as well upgrade to a header and enjoy some more horsepower.

You still need to take the number 2 plug out and see if it is firing . The gap my of got closed up or the plug could of been bad right out of the box. You need to see it fire or better yet just replace that one plug.
You need to run a compression check on every cylinder and compare readings . they should all be between 120-150 and all with 10-15 of each other is very common and a good thing.
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Old 01-21-2010, 05:38 PM   #11
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Thank you Mr. Scott Howard for answering my questions as I deal with this issue, you are a scholar and a gentlemen. I will check on all the points you mentioned and get back to you on the compression test I'll run this weekend.
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Old 01-22-2010, 01:19 PM   #12
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Check the timming, and swap that plug
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Old 01-23-2010, 07:45 AM   #13
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How do I know for sure if my wire and plug are firing, how do I test without getting wacked As far as my fuel injector is there a way to check flow on those without pulling the entire rod out? Is there an easy way to disconnect the throttle cable?

Thanks guys and good morning.
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Old 01-23-2010, 10:12 AM   #14
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Put a clamp on timing light over the plug wire for #2 and see it if fires. If you really hear no change at all when you pull the wire off #2 (especially if you rev it a bit) then I'd say it isn't firing.
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Old 01-23-2010, 03:35 PM   #15
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Would J-B weld work for the crack in the exhaust manifold?
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Old 01-24-2010, 07:32 AM   #16
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Pulled all the plugs and wires just to recheck and the dist. cap and noticed carbon build up on only the #2 cyl's plug all others were clean so does this mean an issue with either the fuel flow or ignition? tried pulling the fuel rod and checking the injectors but could not for the life of me get the injectors to slide out is there a trick?
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Old 01-31-2010, 08:34 AM   #17
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alright kicking the dead horse,

ran a compression test on all cylinders and found #2 and #3 could not push over 30 psi all others were hitting 150. Pulled the valve cover, checked push rods and springs all looked good. Pulled the head of to check the head gasket and found an inch blow out between 2 and 3 bought new gaskets and after 6 smithwicks and 7 hrs decided to wait until today to finish, MAN what a job! and this coming from one who has only recently started working on the jeep Got pics and will post after she's purring and thanks too everyone for their help!
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Old 01-31-2010, 03:04 PM   #18
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at least u found out what was wrong glad we could help u out
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Old 02-01-2010, 06:30 PM   #19
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pics! and she runs like a quite monster! while I was in there I cleaned everything I could see, checked for warping, buffed all the old gaskets off, moly greased all the rockers and fulcrums, changed the oil (got alot of coolant in the oil) and flushed the radiator. Can't wait until I can return the help. Thanks again![IMG][IMG][/IMG][/IMG]

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