All,
As the reader of this thread would know, my last recurring problem is a little bit of oil weeping onto my #4 sparkplug.... I have suspected a leaking valve seal and PawPaw has suggested HighMileage oil as possible fix (it claims to soften and swell old seals). I am running this type oil now.
On the other hand, at this site/page
The Ford Ranger 4.0L Engine - The Ranger Station , which is discussing the 4.0L 6cyl OHV engine, I ran across this quote under the heading of "Known Problems" :
Loose Intake Manifold Bolts - Check for loose lower intake manifold bolts. Pull your #5 plug and check it out. If you see the fuzzy head or have some oil present around the sides of the plug then bingo. The 93-94 have this problem VERY often. Usually you can fix it by simply tightening the bolts (in the PROPER sequence), but sometimes you need a new gasket. Do you notice a loss of oil with no leaks? Say 1-quart every 1500-3000 miles?
So, since the symptom matches mine (except for being an adjacent cylinder getting the oil) I have to wonder if this might be my problem/fix. Unfortunately (at least in the shortrun), I loosened the upper manifold plenum in order to get at those lower intake manifold bolts easier, but realized that I needn't have done that so although I broke its seals loose I didn't pull it up and off. The lower intake manifold bolts were not loose but neither were they very tight. The spec is only about 10 ft-lbs, and I tightened them slightly tighter.
I reassembled everything and when I cranked the engine....it would fire up but would not idle....acted like it had a huge airleak. I checked and double-checked and could not find anything not hooked up correctly, but the engine still would not run. So, I dissassemled back enough to make sure I did not let anything get between the upper intake and the fuel rail it seals to....re-assembled and got the same result, engine dies at idle.
Went to bed last night with a heavy heart, what should have been a quick turn of wrenches had turned into another connundrum....the only thing I could think of was that the figure-8 seal rings that seal the upper intake to fuel rail were not sealing anymore. So, went down to Ford this morning and picked up another set of seals. This time I dissassembled all the way to taking the upper intake plenum off, and when I compared the old seals and new ones, sure enough the new ones were thicker in the vertical dimension and the old ones did not protrude out of the groove (ie, compressed with age). Long story short (and it is a long story, getting that intake off was a real pain) when I reassembled this time the idle returned....back to HAPPY again! And in the longrun, I guess I am glad I wound up putting new seals in, since the old ones were so close to not sealing well.
It helped to read Rockledge's thread in the Technical Liibrary
https://www.ford-trucks.com/forums/2...ke-gasket.html and know that he also had difficulty with the EGR tube too. In my case I disconnected the EGR vavle itself and also unfastened the oil dipstick tube bracket whose stud also holds the EGR tube to the block. Then, the EGR tube lifted up and out (with some contortion) along with the air intake plenum. Then, removing the tube from the plenum was easy. After seeing how the tube is held in place, I would next time try to pull it off as the intake plenum is raised off its studs and removed, rather than disconnect the lower end of the tube.
So, my lesson I am passing on to anyone else is that just because those seals look like reusable O-ring seals does not mean they can be reused with impunity....for less than 10bucks my advice is to have a new set available anytime you break the seal on that interface....it is not worth the trouble I went to to find this out.
Another thing is my lower intake passages had LOTS of varnish in there. This 98 4.0L has 80K miles on it now and in just the last 3K miles I have run some STP and two cans of Seafoam thru the tank.....should I expect to run more thru before I really clean it up much? Even though I have run most of my vehicles over 200K miles with no problems, I honestly have never used fuel additives until recently under the advice that my engine skipping could be clogged injectors (apparently that was not a problem). I am going to try PawPaw's suggestion of "Chevrons Techron Concentrate Plus" as soon as I locate some.
Hopefully I will see an improvement in my oil weeping #4 cylinder, after having tightened the lower intake bolts. If not, I am a little surer that it is a valve seal, as I have previously thought.
Engine is running great though, and I am a HAPPY MAN!
YHS,
rogerw