one fouled spark plug '86 F-150

compression check could be oil fouling

Thank you....

Cylinder head gasket crack leaking oil into that bore?

You say, "There is always a miss"

I'd think the engine should run smoothly with new plugs , at least for a while, till that plug fouls out.

Could it be that you have a flat spot on a cam lobe?

A compression test is okay. A leak down test is better. Do all cylinders.

I the leak down test goes okay, check for a valve guide seal failure or a worn valve guide.

Worn valve guides will lead to a valve failure where the valve head drops into the cylinder. Unfortunately, there is not room for a valve inside the cylinder, so results can be spectacular.

The leak down came easily tell you where the leak is (head gasket, exhaust valve, intake valve, rings) if done right.

A leak down test will normally locate the problem. If oil is getting past the rings due to a loose wrist pin scoring the cylinder, the leakdown test may not pick it up because the resulting cylinder damage is below the piston rings. A bore-scope can be used to diagnose this problem.

If you have a large vacuum leak from a bad power brake booster, ore the PCV valve, you could get your results. Compare your plug to the chart to narrow it down.

Another thing that has not been mentioned is a broken rocker arm, or push rod. For this test you will need to pull a valve cover off of the engine at the dead cylinder. A broken rocker arm, or push rod can still give good compression if it is on the exhaust side. Good luck.

I had an engine that I knew had a bad intake guide in a front cylinder. It was extremely difficult to get at that plug with the AC compressor right above it. For a while, I put up with it and carried a couple of plugs that I sand blasted to clean the oil off. I got tired of that and bought a plug extender to at least keep some of the oil from getting to the plug. Unfortunately, it also kept the plug from being cooled by heat transfer to the engine block/cooling jacket. Cruising on the highway, the plug cooked, blowing out the porcelain, still connected to the plug wire. I couldn't identify the sound and I lost a little power but didn't want to stop on the highway and made it to a service station, in case the car wouldn't start again. By that time, the still sparking plug had melted a hole in the nylon housing of an emission control device ($135 and two weeks. Couldn't find one in many junk yards).

If it's broke and you intend to keep it, fix it now. Waiting could cost you more. Also, If you have worn but not terrible rings (high mileage) and only do the head, you will REALLY notice the bad rings when the valves are perfect again. Keep that in mind if you are not doing the work yourself and have to pay labor costs.

i thought with efi you would not want to go messing with the heat.that it would be best to go back to factory parts and just check and see if the plug is gettin fire. is that wrong? and if i go messing with that what is the worst that could happen?

Changing 1 or 2 heat ranges on a plug that is fowling will not hurt anything. Another option is to use a platinum spark plug. Platinum plugs are harder to foul. It might allow your dead cylinder to operate. You still have the original problem, but it would not be causing any problems. Good luck.

IS the plug oil fouled or gas fouled? One fuel injector can be bad. If oil fouled, intake valve guide clearance problem or worse case broken rings. Usually not rings. What do the other plugs look like. Alot of carbon build up or brown condition.

One injector could be bad only if the engine is fuel injected. If memory serves me correctly, 86 was the last year of carburetors for Ford trucks.

Lots of good advise in previous posts.

If you track it down to oil fouling coming from a bad valve stem seal these can be replaced without major engine dismantling. The critical step is to obtain a compressed air spark plug fitting. The rocker arms are removed and then the cylinder is pressurized with compressed air. This allows the valve spring to be compressed and the keeper removed. The spring can be removed and the seal replaced without removing the head from the block.

Good idea, on average, what pressures are needed?

Also, how do you find out if one valve is leaking oil???? Without dropping the head (lifting?) or having specialized optical equipment, it could be a broken oil control ring for example......

Easy. If the leak down test shows excessive leakage, then you will hear air escaping into either the exhaust or into the intake manifold.

Both make great acoustic horns.

However, you probably need to remove the valve cover over the offending plug to determine if their is valve float or a visually torn valve seal. The valve may seal on its seat, but still push oil into the cylinder.

Another question is what is teh current oil consumption of the vehicle? That would be a clue the it is burning oil. You can also watch the exhaust when the vehicle is under load. Usually a chase car is required.

If the exhaust is blue, then burning oil is suspect. If it is black or white, then probably not. You can also take your finger and sample the exhaust pipe for oil.

Simple and quick solution: use a resistor type plug in that cylinder only. A resistor plug burns hotter than regular plugs burning whatever is in the cylinder.

A hotter or cooler plug depends upon the physical design of the electrode and how it is held in the metal body and with what.

Basically how "far" the heat has to go to be dissipated in the cylinder head. The longer the distance, the hotter the plug basically and very simply said....

For the amateur, you need to look at the manufacturers infos as optically they all appear mostly similar....only an expert can tell them apart all 100%....

The resistor is to do with radio frequency interference suppression......

Before you remove the cylinder head, you need to know what is causing the dead cylinder. Compression testing, both wet and dry will help. Cylinder leak down tests will help.Reading spark plugs will help. They all work to narrow down your problem. One rocker arm adjusted too tight will cause just what you have found. One valve lock retainer that has slipped out of it's groove will hold a valve open.

After your cylinder head is removed and on a bench will be a little late to find this out. Please diagnose before you dismantle.

What engine?

Could very well be as simple as a plugged oil galley and the oil backs up and seeps into one cylinder and/or oil starves the rear cyclinders. The 351C "Cleveland" which became the 351M "Modified" did this quite often unless the oil is/was changed religiously (and while pointing the vehicle towards the western skyline while parked at night... as claimed by many people living east of Omaha--- but this could be nothing more than a romour).

The Windsor didn't have the same oiling problems but you never know!

If I were you, I would add a quart or two of transmission fluid into the oil and then flush the oiling system (drain it/change it) after you put a few miles on it. The transmission fluid will clean some of the hardened crap out of the oil passages.

And go from there.

JL Mealer
Mealer Companies LLC
http://mealercompanies.com

Please explain the path that backed-up oil in the oil galley takes to get into the combustion chamber. It is true that some engines are notorious for developing oil galley related oil starvation problems. I am personally familiar with a few Oldsmobile engines and their front cylinders' valve lifter oil starvation, which not only damages lifters, after years of "ticking" at idle, but also rocker arm fulcrums and cam lobes. I don't have a lubrication system pictorial diagram handy, but that area of the oil galley might also supply the front main bearing as well, although I've never experienced bearing failure even with VERY high mileage engines that have had galley problems. Could be due to the size difference between the supply hole and clearances in the lifter and the bore hole feeding the bearing.

In most pushrod engines, oil gets up to the head and rocker arm area through the push rods. Some do send oil through a bore hole in the block mating with a bore hole in the head which mates to a common rocker arm shaft support and the shaft distributes to the rocker arms. In overhead cam engines, oil is supplied by either that method to the camshaft journals and then the spent oil from the journals splashes onto the cam followers, or external plumbing from the main oil galley supplying the crankshaft is routed up to a camshaft journal for distribution through a camshaft bore hole.

The only way I can see oil from the distribution system itself getting directly into a combustion chamber (not through a worn valve seal and/or guide) is if the head gasket that seals an oil feed bore hole going to the head fails between the hole and a cylinder bore. That would cause all sorts of problems like combustion chamber high pressure gasses being blown into the oil distribution system (bearings don't like air) as well as great amounts of oil being pumped AND sucked into that combustion chamber during the intake cycle. Enough oil in the cylinder will cause it to hydraulic and probably bend a rod at the very least.

One caution about trying to loosen any blockage in the oil galley. Consider where the blockage is going to go once it is free to travel. Into a valve lifter? How about a main bearing? Bearings and their tight clearance also don't like hardened, possibly gritty and sludgy oil. If you know that it is there, it's best to leave it there until the next rebuild. And don't just rely on having it boiled out. I've spent hours on boiled blocks with gun bore wire brushes and a mixture of kerosene and gasoline, a spray can of brake cleaner, a final wash with Ivory dish detergent and a rinse with plenty of high pressure water before it was clean. Blew out the water with compressed air WITH A CHEAP INLINE FINAL FILTER to catch oil and moisture droplets. Let dry in the sun or in front of a fan and then wrap in a plastic bag to keep any indigenous dust from settling on it.

Valve stem seals that are covered in hardened "cheap mixes of 1970's-80's oil" usually crack and seep (at the very least)... I have seen some pretty nasty, oil-encrusted engine cylinder heads in the 80's!

Assuming of course this truck has been around for a lot of miles and is being brought back to a useful life. The encrusted oil could be left-overs from 1986 and that could very well have come from grandpa's milk crate of paper cans of "Yellow Front Super Saver Motor Oil".