87kevroc

Some background first. I had the L98 in my 87 IROC rebuilt (bored 30 over, otherwise stock) last summer. Since that time I have had trouble with the plug in number one cylinder fouling. I took the car back to the machine shop that did the rebuild, they checked to make sure the installation of the engine was done properly. It checked out OK, they recommended I try a hotter plug in the problem cylinder. I could feel the engine misfiring at idle, and otherwise it ran great, but the misfiring got worse. I pulled the plug and it was black, carbon buildup all over it. Installed a new plug. Ran OK for a couple weeks (same symptom, could feel the misfire at idle, but the car accellerated hard, started no problem) until the plug fouled completely.

Took it back. I suggested to the folks at the machine shop the rings or valve stem seals were installed improperly or were defective. They said no, we think its a problem with the intake. I had paid them extra to tank and install the intake manifold before sending the engine back to the mechanic. They removed/replaced the intake, I drove it for a few weeks but the problem persisted. I noticed I was consuming oil, about 1/2 qt per 1000 miles, but the car does not smoke, even at startup. I talked to them again this week and they want to pull the intake again.

OK, thanks for reading this far, here's my question. How can improper installation of the intake manifold cause the fouling of a single plug? I'm trying to figure out how oil can get in the cylinder if not through the valve guides or the rings. I pulled all the plugs yesterday and all had a nice tan/gray color except number one which was black with buildup all over the center electrode. Any ideas? Thanks.

Bort62

Very Simply, if the Intake Does not seal properly, it is very easy to get Oil Into the cylinders, and Just as easy to get it In Only One.


Its possible that Your heads are Damaged In a way taht is Not allowing the intake to Seal properly. Ask them To Scope the motor ( stick a small camera in the park plug Hole ) and Observe If this is Indeed the case.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

86IROC305

I had a blown intake gasket which caused one of the cylinders to suck in oil. It would put out a little smoke at idle when warm, but wasn't consuming that much oil. It could be the intake leaking, but they might also be trying to get away from an expensive problem if it's still under warranty. Most of the valve stem seals I've seen that leak have a single place on the plug from a drip. You might want to try a compression test on the cylinder and make sure the plug is getting fire to it. Just some suggestions....

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86 TPI 305 Iroc-Z
700R4 (rebuilt)
Accel HEI SuperCoil
Flowmaster
K&N Filters
Comp Cams H268 218@.050 454/454

87kevroc

I should have made my topic 'How Can Intake Problem Cause Plug to Foul?' It may be simple, but I can't understand it, and I can't find anybody able and willing to explain it to me. I don't disagree improper installation or a bad gasket could cause fouling, I'm trying to get a clear understanding of *how*. I'll check on the possibility of scoping the cylinder.

What possible path can the oil take to get to the intake ports?

RB83L69

The bottom of each intake port is directly over the space inside the block where the pushrods are. Intake port is on one side of the gasket, crankcase is on the other; bad gasket = oil getting sucked (literally) into the intake manifold. It definitely happens, more often than most people think. I've seen several. It's a real typical new-motor mystery behavior. You may also find thet the "miss" clears up when the vacuum leak gets fixed.

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"So many Mustangs, so little time..."
ICON Motorsports

87kevroc

Thanks RB. But when you say 'Intake port is on one side of the gasket, crankcase is on the other' don't you mean '..cylinder head intake ports on the other'? Or are you referring to the area directly beneath the intake manifold (lifter valley?)? Your first sentence indicates this.

I assumed this area was free of oil. But if oil is there (what would it be lubricating?) then yeah, I can imagine a vaccuum supplied by an intake gasket leak sucking oil from the lifter valley to the intake manifold ports to the head intake ports then into the combustion chamber. Is my understanding correct?

Vader

Kev,

I had a very similar phenomenon on my #2 cylinder. The plug was always darker than the rest, and appeared to be oil fouled. The engine had a slight miss/uneven idle that would be noticable to about 1,700-1,800 RPM. After several plugs of varying heat ranges, compression tests, leakdown tests, vacumm testing, gasket replacements, yada, yada, I still had the problem. It turned out that the injector for the #2 hole had a poor flow and spray pattern. Poor atomization at low RPM and low flow caused ignition miss symptoms. All with under 30,000 miles on the engine/car.

Just a possibility to check before ripping off the heads.

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Later,
Vader
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"Make Me Bad..."
Adobe Acrobat Reader 4.0
KaleCo Auto Parts

RB83L69

Lifter valley = crankcase

You are correct, that area is often referred to as the lifter valley.

There's lots of oil getting slung around in that area. The lifters have oil pressure all around them, the cam is exposed up under there at various places along its length, etc. So I think you have the picture!

"The simplest explanation that fits all the facts is usually the right one."
— Occam, c. 375 B.C.

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"So many Mustangs, so little time..."
ICON Motorsports

87kevroc

Vader, I considered the possibilities a bad ignition component or faulty injector/pulse signal was the source of the problem. But I considered both unlikely because I could not reconcile either with my oil consumption. There's no oil on the garage floor, the engine doesn't smoke, I don't smell it burning on the exhaust manifold and all the other plugs look normal.

I like doing the easy things first, and I hate doing anything to the car when it otherwise runs so well. But all of the above suggest oil is being consumed in number one and the intake (not the head I hope) will have to come off. If it is a gasket, surface imperfection or other small leak, either in the intake or head gasket, I would expect a leakdown test would give the best indication, is this correct? I may ask the machine shop to do this to try and further isolate the problem before going ahead. Thanks for the input.

Bort62

No, A leakdown test will Not tell you if your intake gasket is bad. Other than possbily scopeing Your going to have to take it off and have a look, You may be able to pinpoint where its leaking or Not, Either way when you reinstll take special care to Do it properly.


This is a very common Problem.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype