i got a 94 jeep cherokee 4.0 and my nox reading are way high max is 517 136 is the ave. and i measured 1348 at 15 mph and for 25 mph the max is 770 ave is 124 and i measured 1036. HC is good CO is good. i have narrowed it down to the cat converter or o2 sensor since they control the nox there is no egr valve and to my understanding nox is due to high combustion chamber temps. it seems to run lean and i get better gas mileage than i should which also indicates lean mixture. The cat does not seem to have the "rattle" sound when i tap it so i think it is still good but who knows. I did the spark plugs and cap and rotor and wires since my last test. NOW I NOTICED I SEEM TO EAT UP OIL SO I DECIDED TO START TIGHTING UP THINGS AND THE ROCKER ARM COVER WAS THE FIRST PLACE I STARTED. Every bolt on the dang thing was loose. So i went under neith the jeep and to my dismay i saw an oil leak at the rear seal. is this difficult to replace? how long? diffuculty scale? tools needed? And it get worse there may be a tranny leak because i noticed gear oil all over underneith there to. So the last questions... Where are usual leaks occuring on the 5-speeds. speedometer oil seal?

 

the rear main seal is pretty easy to replace time consuming but easy just remove your oil pan and unbolt the rear bearing cap then you just knock out the old seal it is 2 peice and put the new one back in if you need more info let me now i can take you through it step by step and also you may want to check you valve cover gasket at the rear and the oil filter adapter at the block theyre known to leak and can look like a rear main seal

 

thanks will look at it later today when it cools off

 

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