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Unread Yesterday, 08:56 AM   #1
pman
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Advice welcome: Oil in Air Cleaner; Cylinder 5 low compression

This post is actually on my 88 "Wrongler", but since the carb'd 4.2 is so much more prevalent in the CJ's (and this is where I like to hang out), I felt this would be a good place to ask.

Around 15 years ago I put an Autozone remanufactured engine in the Wrangler. Engine was reman'd by a company called Recon. I have roughly 50k on this motor, and about a year ago I started noticing oil in the air cleaner along with leaking valve cover gaskets, oil pan, rms, etc. At first I suspected a faulty PCV system, so I replaced the valve, and checked the plumbing and all was good. When that didn't help, I checked for vac leaks and again, all good, but still oil in the cleaner. After reading up on this site I knew my next step was a compression test. So FINALLY this weekend I wasn't busy tinkering with any of the other Heeps, and decided to pull the plugs and test. I noticed a cold plug on #5, and sure enough, when I tested compression, all cylinders were around 122-128 but #5 was 60!!! Now, I had also read that the next step is to pour a little oil on top of that piston and see if it raises the number up to confirm bad rings. Guess what Mr Brilliant forgot to do before putting new plugs in and closing the hood? Yep! Didn't try that test.

With that being said, I do plan on pulling all of the plugs again and seeing if the number goes up on 5 with a little oil in the cylinder.

A couple of questions:

-How is this engine even running worth a hoot with that low of compression on that one cylinder? It idles wonderfully.

-If it is the rings on this cylinder, what is the best option? Tear it down and re-ring that one cylinder, or is it time for a full rebuild?

Fuel economy is horrific. My gearing is bad, but it was at around 12mpg and has since dropped to around 8-9 mpg mixed use. I see NO SMOKE from the tailpipe.

The sick thing is that I'm sitting around licking my chops thinking of a plopping a nice stroker in this puppy , but that's just silly. This rig is one of my primary hunting vehicles, so I'm not looking for raw horsepower, just reliability.

I'm open for all thoughts! Thanks!!

Pearsall

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Unread Yesterday, 09:12 AM   #2
gmakra
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First relax, the low cylinder could just be a fluke, if it were me I would rent a leak down tester and do a compression check and a leak down test on a warm engine. Depending on the results of the test you should have an idea which way your headed.
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Unread Yesterday, 09:26 AM   #3
Mike Romain
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My #5 went out also and the symptoms were high blow by like yours. I found a low mileage 4.0 HO from a rusted out 93 Grand Cherokee for $100.00, put all my CJ stuff (intake, carb, ignition and V-belt system) on it over a weekend and have been running that for the last 5 years. I also had to buy an electric fuel pump for $50.00 and another $50.00 to hook up the 4.0 header to the CJ pipe.
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Unread Yesterday, 09:45 AM   #4
pman
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[QUOTE=gmakra;29224153]First relax, QUOTE]

Gmakra, do I sound excited? Actually, I'm not terribly worked up about it, just curious what the best "plan of attack" should be, but definitely will take your advice on further testing.

Mike- I think I stumbled across your story with the 4.0, and that's definitely a good sounding option. I may pick your brain a bit more about that one if I go that route!

From what I've been able to understand is, if the rings are bad on that one piston, does it not make any sense at all to put new rings on that specific piston? Looks like I have to tear the motor down to get to it, so I'm suspecting that's why people recommend a full rebuild/replacement at that point?
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Unread Yesterday, 10:03 AM   #5
Mike Romain
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All your rings need refreshing, you have very low compression all across. My good cylinders were in the 150 psi range.
You can just do one though, if it comes up even, then ok, but if it goes back like new, it should be 150+ which isn't real good, that stresses the bottom end. The compressions are supposed to be within 15 of each other.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread Yesterday, 11:48 AM   #6
Matt1981CJ7
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Compression spec for the 258 is 120-140. So the OP is on the low side, but within spec, in all but the one cylinder.

I'd do the leak down, as George suggested, to isolate the problem, then go from there.

Matt
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Unread Yesterday, 12:08 PM   #7
pman
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Thanks for the responses, gents! I'll keep you posted!
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Unread Yesterday, 12:20 PM   #8
Mike Romain
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Quote:
Originally Posted by Matt1981CJ7 View Post
Compression spec for the 258 is 120-140. So the OP is on the low side, but within spec, in all but the one cylinder.

I'd do the leak down, as George suggested, to isolate the problem, then go from there.

Matt
No wonder my Jeep has run so well, all 3 engines I have had in her had 150-155 compressions.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread Yesterday, 02:26 PM   #9
pman
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Quote:
Originally Posted by gmakra View Post
do a compression check and a leak down test on a warm engine.
George: I started thinking about this. I did the test on a cold engine (read on this or the IFSJA forum that cold was fine, but now realizing this was probably bad advice). It may be the reason why it's a little rough for a few seconds on cold startup, then seems to smooth right on out (I had originally coughed it up to the choke being out of adjustment, but I've got the carb dialed in nicely).

I'll do the leakdown test and update. I always enjoy learning as I go along, and just read up on the various ways that specific test can help you diagnose issues.

Thanks again George, Matt and Mike.
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Unread Yesterday, 02:31 PM   #10
billiebob
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Oil in the air cleaner is usually a faulty PVC valve. A real simple cheap fix.
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Unread Yesterday, 02:44 PM   #11
pman
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billiebob-


You'll have to read my original post at the top. I ruled that out right away. I certainly wish that was the problem!
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