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Unread 06-08-2009, 08:10 PM   #1
gman781
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Misfire on #3 please help?

Any suggestions please. I had a jeep dealer sevice my jeep with a fuel clean trans and oil change. 5 days later my check engine light comes on. It was a misfire on #3.

I brought it back to them and they run some tests and say that I need a valve job to the tune of 3000 dollars. I say it wasn't giving me a check engine light before I had them work on it, They said nothing they did caused it.

I have since replaced the coil, plugs, AST relay, switched the coil packs betwwen 1 and 3 and the fuel injector between 1 and 3. It is still coming on for #3 misfire.

I tested the ohms on the fuel injector and the coils and they all were around the same no mater which one I checked. I also checked the VDC on the coil pack plug and it was anywhere between 11 - 15.

Any suggestions would be heplful please, I also cotacted the headquarters and all they did is call up the dealership and came back an said nothing they did caused the problem go figure.

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Unread 06-08-2009, 08:50 PM   #2
nhcd538
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Probably a broken valve spring at the #3 cylinder. Common problem with the 3.7L, and it probably wasn't the dealer's fault, just a coincidence.

$3000 for an entire valve job...maybe a bit excessive. All you need is a new valve spring on #3. Labor costs $$ though...
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Unread 06-08-2009, 09:50 PM   #3
nubby
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same but on #4

i was having the same issue but it was on cyl #4. im in the process of swapping out the engine now. run a compression test and see how yours falls in the specs, it might be cheaper in the long run to go ahead and swap the motor with a low mileage pull out or a reman. remans are running about 2500 to 3500 ( and jasper the most expensive)
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Unread 06-09-2009, 07:45 AM   #4
oldfamilyguy
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don't drive it any more until you know for sure. if the valves drops, then you can end up with a broken piston and scored up cylinder wall, a lot more than a valve job. get the valve cover off and see whats going on.
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Unread 06-09-2009, 07:55 AM   #5
gman781
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I have not had the problem again Sat so I am keeping my fingers crossed they did do a compression test and #3 was at about 140 while the others were at 190.
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Unread 06-09-2009, 08:24 AM   #6
nhcd538
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Quote:
Originally Posted by oldfamilyguy View Post
don't drive it any more until you know for sure. if the valves drops, then you can end up with a broken piston and scored up cylinder wall, a lot more than a valve job. get the valve cover off and see whats going on.
Very true...you obviously have a valve spring going south there. Get it in and have someone change the #3 valve spring before it turns into a much more involved job.
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Unread 06-09-2009, 09:29 AM   #7
oldfamilyguy
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crossing fingers and hoping won't do it for this. the low compression says it all. deal with it now or look at replacing the entire engine
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Unread 06-09-2009, 11:05 AM   #8
XR
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You're still driving it?Don't cry when it leaves you stranded with a really large repair bill.
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Unread 06-09-2009, 05:54 PM   #9
TJJP77
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If it's not a broken valve spring, it could be a valve that stopped turning and has begun to take on more of an oval shape, thereby failing to seal when shut. I've seen that before on these engines. You really should do a cylinder leakdown test to determine why you have low compression.
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Unread 06-10-2009, 06:56 AM   #10
gman781
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Could it be the plugs that are in the engine? I used NGK plug and I have read that you should use Champion plug in this engine?
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Unread 06-10-2009, 08:25 AM   #11
jp7794
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Afraid not my friend. A loss of compression is something internal.
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Unread 06-10-2009, 08:54 AM   #12
sdowney717
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If the valve spring is OK, then you might as well just drive it. You can try some BG44K top end cleaner. It could be carbon on the valves. Or you could put some Dexron ATF in the gasoline. 1 qt per 20 gallons for a couple months and see if it helps. ATF is a very good cleaner. I tried a lot of fixes, but if it is mechanical wear issue only a teardown will fix it. I seriously doubt the mechanic caused anything to go wrong.

I just went thru this and turned out the head had warped. cylinder 3 was only 30PSI. Ran pretty rough. occasionally would get SEL light. The exhaust valves were also leaky on all the cylinders. It just wears out. There was 185,000 miles on the 4.0l

rebuilt it. cylinders were perfect
costs were
50$ head resurface, shaved off .012 bunner machine shop, Hampton VA
lap ground the valves myself $4 for grinding compound autozone
new mains $23
new rods $17
new upper gasket set 50$ ebay
new main seal $10
new moly rings $38
new water pump $36 autozone

got the internals from here very good prices!
http://www.enginepartsstore.com/servlet/Detail?no=1012

go with moly, they are much more durable than cast rings.
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Unread 06-10-2009, 08:55 AM   #13
nhcd538
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Quote:
Originally Posted by TJJP77 View Post
If it's not a broken valve spring, it could be a valve that stopped turning and has begun to take on more of an oval shape, thereby failing to seal when shut. I've seen that before on these engines. You really should do a cylinder leakdown test to determine why you have low compression.
TJJP could be correct here.

However, it's most likely a bad valve spring. The reason I suggest that it's probably a valve spring is because it's just so common on the 3.7L motor, been seeing it alot lately over on the other KJ forums. Remember that this is the 3.7L, not the 4.0L so alot of what is being said above doesn't apply to you. These 3.7L engines rarely have warped heads, and rarely have valves turn and change shape (although I suppose both are possible). Meanwhile, they frequently need new valve springs.

Seriously gman, compared to tearing the whole engine down, replacing a valve spring is really a nothing job. You should ask around about the cost of getting it done. Man if that spring fails and that valve drops, you're done.
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Unread 06-10-2009, 06:50 PM   #14
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Quote:
Originally Posted by nhcd538 View Post
These 3.7L engines rarely have warped heads, and rarely have valves turn and change shape (although I suppose both are possible).
Warped heads will generally only occur in an overheat situation, so unless the OP overheated it, the head is probably ok.

As far as the valve issue - all engines need the valves to turn for it to maintain a good concentric seal...this is designed into the valvetrain, usually in the shape of the rocker tip and by off-setting the rocker contact point in relation to the valve tip to force the valve to spin. It usually requires some RPM (over 3,000 RPM) for this to occur, so folks who really baby their engines are actually doing themselves a disservice. When a valve stops turning from either carbon build up on the stem or overly light operation, the valve head begins to take on a slight oval shape, causing a poor seal. While you may have never seen this, there was in fact a TSB for this issue for 2005 and 2006 KJs. I'm not sure what model year KJ the OP has, but who's to say it can't happen on other model years?
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Last edited by TJJP77; 06-11-2009 at 08:14 PM..
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Unread 06-11-2009, 04:11 PM   #15
Thunderstrike
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I know this is Liberty, but for Wrangler we have a TSB on #3 cylinder misfire. The fix is to get the fuel injector insulator and install it.
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