[Amc-list] Help diagnosing 4.0 loss of compression

[Jesse <j2sax@xxxxxxxxx>]

SO I called on a shop today that is having a problem with a BEAUtiful 90 4.0 Cherokee.  He's maintainted this for an elderly customer for years.  

SO the old fellows cruising on the highway, Chero is running great and says he thinks it's overheating becuase he hears pinging.  As he starts to pull over it dies and will no longer starts.  Hasn't started since.

So the shop gets it figuring fuel pump or something in cooling... everything checks out.  Coolant is good with no oil, oil is good with no coolant, though it smells like it has gotten hot.  

Timing chain?  Put number one on the mark, dist rotated properly to #1... seemed tight when rocked back and forth.  

Here's the rub... ran a compression test and all cylinders almost dead.  SO how was it cruising the highway great and suddenly all cylinders are down?  Head gasket doesn't typically die that evenly.  

Tech put oil in a couple of cylinders and saw no improvement.  

I am thinking contaminated fuel or oil causing extreme cyl scoring?  The tech is thinking something similar that flattened out the cam.    

Any ideas?  I told him to yank the valve cover and put a dial to the 'train and see what kind of action he's getting.  If not there, it sure feels like rimgs to me.  How did they all die so quickly from running so well AND with no report of smoke?  

Your experienced help is appreciated, 

Jesse




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