Author Topic: Helping some one out (JK 3.8l compression issue)  (Read 1507 times)

Offline Magnum Opus

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Helping some one out (JK 3.8l compression issue)
« on: January 27, 2016, 03:08:52 PM »
I work with a guy whoose son has an 07 JK with about 60K on the engine.  The kid ain't much of a wrench and his rig is stock (mall crawl no rocks) daily driver.  The rig left him stranded got so bad the truck went into protection mode and parked itself.  Got him towed and had a mechanic look at it.  He found one of the Catalytic converters plugged on the drivers side and cylinder #2's compression at 60 psi (yikes) all others at about 100 psi (not cool).  They are going to pay to get the broken cats fixed, but are hesitant to pop the head due to budget.  My thoughts are that it has been about 60K miles at low RPM running the cheapest gas he could feed it (college kid), resulting in severe carbon build up on the valve train. 
     Thinking about after the cats are fixed pulling plugs and hosing down the cylinders with wd-40 or pb blaster, rolling it a couple of times and letting it sit over night.  After which chucking some new plugs at it and driving it like we stole it for a good run to blow the soot out of it.  Then following up with a regiment of good gas, sea foam and a standing order to select a lower gear (manual) and keep the rpm up a little higher. 
     Does this check with logic or am I reading too much snake oil garbage on the internet?  I don't think they have the stomach to pull the heads and do them right, and I don't want to advise them to pull one head and go after just cylinder # 2, especially when it could be just dirty.
     Please deposit your 2 cents!

Offline toreadorranger

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Re: Helping some one out (JK 3.8l compression issue)
« Reply #1 on: January 27, 2016, 04:13:11 PM »
Id do a leak down test, it could give you some more info on what the issue is with the low compression.  I wouldn't spray the cylinders down with wd or pb, I would use a little bit of ATF, let it sit over night, then crank the motor over without the plugs in. 

Offline Magnum Opus

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Re: Helping some one out (JK 3.8l compression issue)
« Reply #2 on: January 27, 2016, 08:13:09 PM »
The mechanic was certain it was not the rings and that it was definitely the valve train, so I am 80% confident that a leak down test was done at Le Blancs.  No way I could know for certain unles I went and asked the mechanic, but I am comfortable with the report.  I did find out for sure that the cheapest gas attainable and low RPMs have been the driving habit for at least 30K of 60K miles on the engine.  Those habits will be corrected when the rig gets fixed.
     I never thought about ATF......that is going to smoke like Cheech and Chong when we first fire it up!  Gonna have to make sure we light that thing off outside!  Next up will be aquiring a compression gage.....I am guessing harbor freight will be as good as any for retest.
     Looks like we will probably be doing this science experiment next week end.