Air Filter Sucking Oil
[This message refers to 4.0 Cherokee motors but I think it
will also apply to YJ 4.0 motors]
>My 1987 4.0 FI XJ has started sucking oil into the air filter.
>It then dumps the oil on the ground. The local mechanic, says
>the oil rings are shot. He says it is cheaper to buy a reman
>than it is to overhaul the engine.
Before giving up on your 87 4.0 due to the oil in the filter
try a little clean up on the Crankcase Ventilation system.
Its not a traditional PVC valve system.
The large tube from the rocker cover is an air intake vent,
filtered air, from the air filter. The small tube at the
back of the rocker cover is supposed to always keep the
crankcase in a vacuum to keep the air & oil moving the right
direction. This usually keeps the air and oil in the large
tube traveling in the direction of the rocker cover.
The gromet holding the small tube at the back of the rocker
is supposed to have a 0.1 inch orfice to meter vacuum. Its
just rubber and gets plugged periodically. When it plugs,
you lose the vacuum in the crankcase, the large tube becomes
the crankcase vent (in and out) and full of oil. The large
tube entry has no baffle plate in the rocker cover and it
makes a mess that can lose 1 qt per 1000 mi.
Pull the small tube out of the gromit and stick a drill of
the appropriate size into the hole to clean it up, a 1/8 in
drill is close enough. Dont be shy as there is a baffle
plate under the gromit to keep you from hurting anything
important. Other things to check when you find oil in the
filter is a gummed up throttle body. The idle air solenoid,
front of the TB on the passenger side with wires out of it,
can also get gummed up from the oil. Clean up the inside of
the throttle body with carb cleaner spray and remove the
idle solenoid to clean the air valve. I also check all the
wiring connections, pull them apart and reseat them.
When complete the idle should improve and you should be able
to feel a vacuum in the big tube pulling from the crankcase.
I do this about every 20k with my 88 4.0 and have 194k+
miles, passing the CA emissions test with original
everything, etc. BTW, a master rebuild kit is about $600.00.
Ed A. Stevens