Oily plug-valve guides or piston rings?

have a 90 bronco w/ 302 efi. back right plug has oily residue. plugs are brand new(less than a month old).gaped to 54 like the manual says. Hesitation at higher rpm especially in 3rd gear and especially pulling hills. just got new plugs, wires, cap, rotor, serp. belt, coolant temp. sensor. question is if only one plug is oily, obvious cause the anti seize on that one plug is liquidy, unlike the rest which were dry, is it worn valve guides, or piston rings. and do i need a whole engine rebuild or just a top or bottom rebuild. engine runs strong otherwise. And if i do need to rebuild something any suggestions toward adding HP with aftermarket high performance parts would be great. such as cams, valves, pistons, roller rockers, etc. I am amatuer, but eager to learn. so any tips appreciated. Thanks

Start with a compression test. If the compression is good and equal in all cylinders suspect the valve stem seals.

By the way, A “top or bottom rebuild” is really a misnomer. While you could remove the heads, rebuild the bottom end, and put the same heads back on and maybe get away with it, why would you? It makes far more sense to do the valves, test or replace the tired old springs, replace the stem seals, be sure the surfaces are flat and good, etc. when the heads are off than to just bolt the old heads back on.

As to rebuilding the top end, with the exception of just replacing the valve stem seals is fine but it you’re going to do all the rest to the heads do you really want to bolt them onto a tired old 19 year old lower end?

Oh, and if you really do go for a rebuild and are considering adding horsepower the best place to start would be porting. “Porting” is really just opening up the intake and exhaust ports to allow freer flow of fluids for more volume through. That improves your ability to move fuel in and exhaust out. Then you can put on a higher capacity (CFM, cubic feet per minute) carb, a lower restriction intake manifold, and headers and improve performance without the compromise to daily drivability that a performance cam would bring with it. Of course porting also allows you better use of a cam too.

The easier you can get fluids in and out of the chambers is the better off you’ll be. Do that without adding compression or a cam and you can get improvement while still maintaining drivability.

Of course, if drivability isn’t an issue then start looking at new heads, new pistons and rods, new cam, etc. $$$$$$$ will become the issue. New cam means stronger springs, roller rockers, and other stronger components…new heads, like I mentioned.

And then there’s supercharging…

JMHO you understand.

All good points. I have been looking extensively for a lower milage engine that has all ready been bored out and raced up a bit. Ive found some for between 2000-4000. for this same 2000-4000 could i bore/polish and rebuild with new higher performance parts myself. labor would be done myself with family. And if you know about this sort of thing what are the different cams available and whats the difference. RV cam, etc?

Is the plug simply oil soaked or is it oil fouled causing a misfire? Check these links, there is one for Edelbrock and look at thr Brake and Front end link as there is much more the Brake info. on it. http://www.delmarlearning.com/ase/weblinks.htm

All ready have 2.5 in headers to 3" exaust.w/ flowmaster. not sure about the porting. only had vehicle 4 months. i would like to add the extra horse power for fun off-road, and better towing of motorcycles and 20 ft or less boat. so drivability is good, but so is fun. had intended on keeping it EFI, not carb.

A lot has to do with who rebuilt it and how well it was done. Rebuilding an engine yourself takes time, space, patience, and a big investment in tools. Every piece needs to be measured, clearances checked with plastigage, everything tested and checked, springs tested, everything cleaned, resurfacing.

I don’t know about what’s available for that engine, but performance cams will either hold the valves open longer (high duration) or/and open them wider (high lift). But it’s a system. You open them longer or wider you need stronger spring to close them faster or the “float”. Then you get into stronger rockers and other pieces to withstand the strain. Everything affects something else.

How far you go depends on how much money you have and how much of a compromise you’re willing to make in reliability and daily drivability. More power comes from bigger bangs, bigger bangs create more stresses.

If you and your budget are up to it, by all means get a manual and consider rebuilding it yourself. It’ll be a great experience.

OK4450 is really the expert in souping up engines. He’s “the man”. I hope he joins us here.

That may make it easier. Perhaps the chip can be reprogrammed to increase pulsewidth.

You’d need to do some research, but that may be easier on the budget that if it were carbed. Sorry, I admittedly missed the efi in the original post. I have old, tired eyes.

I have to guess rings for that amount of oil. Specifically the oil ring being stuck because of too much crud baked onto it. There were times when the backyard mechnics would set that cylinder on compression stroke and pour about ten ounces of penetrating oil into the cylinder, let it sit overnight, put some more in and screw an air hose into the spark plug hole and pressurize it. Sometimes it would even work.

Option 2: Remove the intake manifold and scrape the crud off the intake valve. Sometimes the crud will take up most of the opening and block it off, causing the vacuum in the cylinder to increase, pulling more oil up past the rings.

It seems to be a back right cylinder problem to me. I had one do that on a 350 Chevy. I had the time, so I “rebuilt” that engine. The oil ring was full of crud.

I remember about 35 years ago an old mechanic telling me he would clear up stuck-crud-filled oil rings by adding a lot of kerosene to this oil, drive for 200 miles, then drain and refill with fresh oil. He said it worked every time.

I don’t remember the ratio he used - I want to say it was 50/50 oil-to-kerosene.

He did caution that the pan may need to be dropped to clean out the oil pickup screen.