Fang333333

Allright folks, there has been several threads started from this Corvette curse of mine, however I have a new theory.
For more details and videos I have another thread called "pretty disapponted..." But my question now stems from something I noticed. My car has been, afterfiring, backfiring losing accel, losing a cylinder difficult to keep timing. I have done a compression check, rebuilt the distrib with help from another member, rebuilt the carb to spec, timing, I could go on and on. Despite the trouble everything checks out good. Today I finished my first leakdown test and AGAIN everything is in the green. I took notice of ONE sparkplug that is fouled. Now before I had done a tuneup I noticed the old plug in this cylinder was fouled. A few months later checking the replacement plugs, this one was again fouled and then again today it was fouled. So with a passing leak down test, I took the plug, cleaned it and popped it back in. To my shock the car...the car now works. It could be coincidental, as my problem is intermittent and never steady, however all night it has been running smooth. Like I hit some kind of "Troubled Engine" on/off switch. I had one burp through the carb and its back to smooooth all night. Night and day difference. I'm sure this plug will foul again soon...

There may be more leakage from this cylinder but its still in the green. Only hissing noises from escaping air @30 psi comes from dipstick and it is minor, (the leakdown tester is louder than the hiss). All cylinders are about the same when it comes to escaping air noises. Their really isn't any noises more of something barely noticeable. So what is going on in there!!!? All other plugs are consistent, just the cylinder closest to the passenger is trouble. I adjusted valves, so what gives?
If it matters I did notice my harmonic balancer TDC has moved and might need to be replaced but as it is the car does run smooth. What causes ONE cylinder to constantly get fouled? Even after cleaning and plug replacement. Even with a passing leakdown and compression. Everything in distrib checks out.
Thanks Corvette Fam
I maybe be close to something here.

Big2Bird

Bad valve guide/seal. Broken/bad oil control ring. Bad intake gasket. Closest intake runner sucking in something.

SH-60B

Fang, I read most of your previous posts. I must have missed the one mentioning the fouled plug. If you're "lucky" the problem will be confined to that head.

OMF

Hi Joe,
Glad to hear you found something solid. Change those valve seals, or if there is none on the the valves, put some on and see if that solves the problem. I can't remember, what heads are on your car, are they stock heads?

Forrest

MelWff

have you tested the spark plug wire by either using an ohmmeter, 1k per foot of wire, or switching the wire with another cylinder to see if the fouling moves with the wire?

Fang333333

Hello my friend, I was gonna contact you when I had something better to report lol!
Yes I am thinking valve seal job. I have a compressor now so I should have everything I need to to keep the valve from dropping and do the job...we shall see!
PS this was that same spark plug we talked about and I had kept in eye on it as you said.

Fang333333

Yes even replaced wires

Fang333333

Thanks SH
You did not miss anything, I was more worried about compression, distrib, and really did not give much thought to the fouled plug. After months of replacing and recleaning, I have finally established that there is something constabtly fouling this guy.

mikem350

#8 cyl? It is known that #8 cylinder has to deal with more oil flowing back down to the pan, due to the slope of the engine.

Take the suggested oil control fixes!

donaldb1

[]I have seen No.8 plug be fouled by transmission fluid being sucked into the intake runner coming from the trans vac modulator .

Fang333333

How would one fix this? Or what to look for? Also any recommendations on valve seals? I bought felpro oring and umbrella seal but they look quite unimpressive. I hear others require machining?
The #8 fouls rapidly within 5 hours. I really want this to be stem seals....The car had sat for quite along time in AZ weather

MelWff

the reference to the vacuum modulator would mean the modulator is shot. Assuming you have an automatic remove the line from the modulator on the side of the transmission and look for transmission fluid.

BLUE1972

Usually a crappy PCV valve causes the fouling also..

It's supposed to also limit the vacuum pressure in the crank case as well as suck in the fumes. Most genetic replacements allow too much vacuum which cause it to suck oil in the PCV valve and also suck oil past the guide seals.

Change the plugs and pull and plug the PCV. Drive for a few days if the problem stops it's the valve. Get a real GM valve.

I would also check the guide seals - if dry or worn - change them.

Fang333333

I thought this as well, my PCV Rattles constantly on idle and everything so I replaced it. Still does the same. I assume its high idle may cause this.

I am getting ready to do valve seals with oring and umbrella seals. THE CORVETTE CURSE CONTINUES! We got hit with bad weather in Northern AZ so I am literally just sitting in a chair looking out the window in frustration. I waited 7 months to get this far...now I have to wait longer. Oh well. If it is not seals I may need to look into tranny
...no
Not that kind of tranny.
Anyway I wil update when I get answers.

OMF

I can tell by your enthusiasm your getting close.....

Fang333333

Thanks Forrest, I completed valve seals today, also did a full Sea Foam treatment (Generally I do not do additives but I must say Sea Foam has been a positive experience). AND FULL OIL FLUSH AND OIL FILTER CHANGE. Unfortunately the seals were not all that bad. They were missing O rings but the umbrellas were flexible.

It still kills #8. Multiple people say it is oil when looking at it. Many doubt it is a ring do to the compression/leakdown and engine performance. I may try pulling the PCV. THE PCV DOES RATTTLE CONSTANTLY. I am considering an anti foul plug but I find it real discouraging that #8 is flooding with oil.
The valves themselves were SOLID. No movement. I could literally shake the engine holding onto a valve if I wanted. There is 0 movement.

Does the passenger side need/have a pcv? Mine just has a breather tube.
This oil seepage is definitely 80 to even 95% the issue.

There appeared to be no excessive noise when filling #8 with compressed air. It almost seams impossible in my mind that oil could be accumulating.
I wonder about the intake. There are minor exterior oil leaks. Nothing excessive. I wonder about stress cracks in the engine but find it hard to believe that There could be a fissure that would not show other oddball behavior ie pass a compression and leakage and not have major performance issues.

When the plug is fresh the engine generally runs smooth. It even hums. It just doesnt last that long. Once she goes for a few hours the engine turns to pure 💩. NO NOTICEABLE exhaust smoke...

Fang333333

Bird could you elaborate on "intake runner"?

How hard is the intake gasket to replace?

OMF

When he says intake runner, he means the port on the intake manifold that supplys the fuel/air mix from the carb.

An intake manifold gasket is really easy to replace.
- before you do anything, use your new compressor and blow off the top of the engine removing all dust and debris, focus on the joint between the heads and the intake.
- Drain coolant from rad until coolant level is about even with the bottom of the heads, or just drain the rad completely.
- Disconnect all the fixtures on the intake manifold... throttle cable, transmission cable, vacuum lines, fuel line to carb, coolant temp, rad and heater hose...you can leave the carb bolted on if you like.
- To make it easy for reinstallation, bring engine to top dead centre, remove the cap and mark on the side of the distributor where the rotor is pointing. Next scribe a mark on the distibutor base and the intake manifold. Were doing this so you can line up the marks when reinstalling and get your ignition timing close enough to start the engine.
-When you remove the distributor the rotor will twist as you pull it out, make a mark on the distributor where the rotor stops, this is important for reinstalling it.
- Now just unbolt the intake and remove it off the top of the engine.
-No matter how hard you try, some crap and coolant will fall into the engine, just clean it up as well as you can.
- Inspect the gaskets for signs of leakage prior to removing them, focus on the lower edge of that #8 cylinder.....take a pic and show us what you found

Fang333333

I'm going to just go out on a limb here and say you seem like a man whom knows how to read and write checklist on a proffessional level...Just a hunch..Thanks for this, it is very concise, easy to understand and answers everything that I would have issues with.

Heres an update...I have not torn into the manifold however I did a install an anti fowler....those headers made that pure joy, anyway after installing the anti-fouler the AFTER FIRING RETURNED BUT EVEN WORSE...
....NOW SHE SMOKES.
Every once and awhile I get a flood of greyish smoke on accel. The plug has seemed to at least kept the #8 working but she runs rough on idle (not as bad as a dead cylinder but she constantly "bumps" 50 rpms and loses gains an even 100 rpm (750 idle down to 650 with constant "bumps" of 50 rpms. The smoke has me at an all time low as I have never seen smoke from her except that minor start up vapor. So I contemplate the next move.
Do I attack the intake still?
Do I instead now remove heads?
Or do I pull the bottom half of the engine out

*Define Irony, man installs valve seals only to have his car smoke for the first time days later.

I neglected to mention that on another cylinder (on the problem side) I noticed about 3/4 an inch of an inner valve spring had broken off upon removal (seemed very minor and I was advised it should not have been an issue. Again it was not the #8 or I would gave been replacing springs) I'm just spewing every last tiny detail as to what I see. The outer springs were fine and the valves were tight and springs were super, um, springy.

Anyway #8 has bad oil leakage that decided to spontanously smoke. Part of me clings to hope that this is somehow Sea Foam... Except I flushed the oil.

Also oil pressure is high around 2k, 2.5k. She will peg the needle when its cold out and go down as warms. The PCV rattles. Even after replacing.

Thats what I got. So if anyone can tell me where they would go from here I would love it. I have tried everything except removing PCV.

All of you have been so great...
If intake is still the direction to go than let me know. I am also asking my mechanic friend but literally everyone seems to be baffled... There just seems to be no solid indications of one thing or the other to attack the problem.

Oh Forrest I got my headlights to work. I had never seen them work before. Replaced the whole System.

BLUE1972

Pull the PCV, plug the tube and drive for a day or so. Put in a vented cap in the PCV valve hole.

If the cap fills with oil you have a blow by issue / clogged oil returns.

If the engine runs better with less smoke - you are sucking oil from the valve cover with the PCV valve.


It's a cheap test and almost painless...