Spark plugs: 7 tan, 1 black

[ceslaw]

My Cobra has 2500 miles, so I decided to change the plugs. It has a 427 Genesis sideoiler, Holley 850 CFM carb. Runs great - no complaints. Seven of the plugs had a nice dark tan color. No significant carbon or oil. But one was black and grimmy. The car uses about a quart of oil in 300 miles. No oil leaks whatsoever (hard to believe!). Any ideas why? Should I be concerned about that one nasty looking plug?

Chuck

[MacGyver]

With such low miles on the engine using an above average amount of oil would not be a big suprise but one quart per 300 miles is way out of line. I would suspect a valve stem seal has popped loose or didn't get installed correctly to begin with. There are methods of using compressed air in the spark plug hole to secure the valve so you can use a spring tool to remove it for seal inspection & replacement. If not addressed soon you risk the danger of badly carboning up the rings in the offending cylinder. This would mean major dissasembly. If you paid someone else to build this engine it should be a warrantable issue. Other far worse possibilities could be but not limmited to an oil galley leaking past the head gasket, lined up ring end gap or broken rings. If you have access to a bore scope you could take a peek in the offending cylinder with the intake valve open & inspect the valve & cylinder walls for clues.

Gorgeous car by the way!!!!!!

Matt

[Burgs]

I once used a cloths line, fed into the spark plug hole with the piston down, then raised the piston up to compress the clothes line into the valves, to hold them in place to remove the springs and replace the valve seals.

[trularin]

Might want to check the wire to the blacked plug.

[Traveller]

I looked at your pictures and I think I see your problem.

Your engine is too clean. In order for an FE to run properly is must leak oil out of several hidden spots know only to a select few Ford execs and the chairman of Exxon.

[vettestr]

All good info submitted already as this site has a lot of experience to offer help to its members for sure. This could be as easy as a bad plug or wire but the whole picture needs to be checked. The oil consumption is a real clue so jump to mechanics of that cylinder. I do not think just a bad or missing valve seal is the culprit but maybe a bad valve guide, leaking intake gasket or poor piston to cyl. wall sealing would allow the amounts you are seeing (again you said no external oil leaks so it is burning the oil)
Do a simple vac. gauge test and look for a fast flutter on the needle for guide test. Do a compression test to check piston/cyl. seal with a leak down test if needed to isolate issue ( you can hear were air is going ). I skipped the simple bad wire or plug or even carbon tracking on distrib. cap because of oil consumption as reason for just 1 cylinder being fouled. The leak down test tells you more for cylinder mechanics but a leaking gasket or bad guide will not show up as quick with a leak down test. The Vac gauge reading with all the parts moving real time takes you through the different loads/side-loads imparted on things like the V. guide. You did not mention if you had oil contamination in coolant, check for milkshake in expansion tank or rubber hoses getting soft or oil film on exterior of hoses.
Again the amount of oil this bad boy is drinking is what I am concerned about and fouled plug is just a symptom of real issue. I hope I am full of BS and a new plug wire makes all better.

[Nantucket427]

Alloy piston in an cast iron block never let the rings seat properly. I chased it around for over a year. Too much oil in the heads, pcv valves, plug wires, plugs heat range, etc, etc. I knew I was in trouble as soon as I pulled the heads. Be fully aware not everyone knows how to machine and build a FE. I went to one of the best Miller Machine Haverhill MA. Car runs great NOW!!!
Cost $8,000.00, having the car back to drive priceless.

[ceslaw]

Really good thoughts.

Thanks for all the feedback. It is reassuring to now there is so much support out there from someone with little experience working inside an engine. Here is my plan of action:

1. Carefully monitor oil consumption, rather than just guesstimating. I have been adding a cup here and there rather than letting it get down a quart. So my estimate of oil consumption may not be accurate.

2. Pull the new plugs and check them in a week or two after I have some miles on them. Perhaps it was a plug problem. (Hope springs eternal).

3. If the new plug in the suspect cylinder is black and grimy, then pull off the valve cover, do a vacuum check, pressure check and pursue some of the avenues suggested. These are new areas for me, so sounds like I may be investing in some new gadgets, getting back on this forum, and asking more questions.

I guess I am in denial. It is a new engine, good quality parts, low mileage, and just runs too good to need a major repair. We will see. Thanks for the excellent ideas.

[vettestr]

Your plan sounds well though out and reasonable. I might suggest you swap the plug wire with another cylinder while you are at it. Pick another cylinder that has about the same length wire and trade with it. If problem follows the wire then easy fix and if same hole gets fouled it helps you confirm the cylinder anyway. Wishing you the best
Jeff C

[68gt500]

Two more thoughts:
Do you have a PCV? Maybe the PCV is sucking in oil from the valvecover.

A leaking intake gasket could very well allow oil into that one cylinder.

[undy]

That's also a classic symptom of a leaking intake manifold gasket. (vacuum leak and sucking oil into the intake tract) FE's are very prone to that too, not the best design.

[mr0077]

undy, you beat me to that possible cause. If it is a leaky intake gasket it will show as oily traces in the cylinder port and none (or very slight traces) in the intake port, and carbon deposits and crud on the top (back side) of the intake valve.

One last suggestion: if you have Edelbrock heads (not sure if this happens on other brands), putting the rocker bolts in the "rong" hole will cause the bolt to "punch through" the top of one of an intake port in the head, and the motor can suck oil past the threads; again, it will show as an oily trace running from the punched hole in the top of the port to the intake valve.

[ceslaw]

Thanks for all the input. I am going at this slow. So here is a bit more info.

I have driven another fifty miles or so since changing the plugs. It runs just fine. Pulled a couple of plugs tonight and the problem cylinder is already getting grimmy and the other is slightly tan and dry. So the problem was not something simple like a bad plug.

But what was interesting was the puddle of oil at the spark plug opening. All around it was dry. Oil only in the spark plug hole. The threads were oily the full length.

I have not yet swapped out the plug wire or looked inside the distributor cap. I may pull the valve cover next to see if there is anything obvious.

[vettestr]

Hey Chuck,
For the plug to show fouling after only 50 miles it has a significant oiling source so this should be easy to isolate. You said you are not a serious gear head so the tools needed for these tests are cheap and easy to find if you do not have them already. A vac gauge is maybe 10 bucks and very useful tool and compression gauge is a rent-able tool but a good one is only maybe 30 bucks but maybe not a tool you will use often. Get 1 that stays at max pressure reading until cleared by user. Cheaper ones must be watched as they return to zero without pressure applied. PS... Remove coil wire during test for a couple of reasons. Do a vac check next as this will tell many things. Record vac. @ an idle (10 to 20 inches depending on cam etc. is expected) and then at say 2500 rpm but give it about 30 seconds at this steady rpm before recording reading (same or near idle reading expected). Now look at idle vac again. Look at needle condition not reading = is it steady or is needle vibrating at a swing of maybe 5 -10 inches on gauge? Is there any sign of oil in coolant (check cold engine to be safe) I am leaning hard to either a manifold gasket around head port or the bolt length that can break into port runner. Good on 0077 for his post as a possible. Look at hose end from the PCV valve as it attachés to intake or system to see if it enters near or where oil could be dumping oil into the affected cyl. = I think this is a stretch as it is fouling plug so fast but agree they can suck oil and create problems. A leak down test is best way to isolate issue but at this point and fouling speed a simple compression test will show good or bad hole. Please let us know what ya find?

[ceslaw]

Jeff:

Thanks for the tips. I am on my way to Sears or Autozone to get a vac and compression gauges. Will let you know what I find.

Pulled off the valve cover this morning but could tell nothing from a simple visual inspection.

[vettestr]

Chuck,
I get a kick out of reading the circa 1965 to maybe 1970 Motor manuals. You can find them in garage sales or where ever but the true Motors manuals have a ton of diagnostics and test procedures that you just can not find in other places. They take you through step by step test and rebuild areas that use common shop or hand held tools. These hot rods can be worked on and I enjoy doing that. This is my sanity check from the buzz of the regular world, I just go play with my toys.
This is before todays $80,000 and up diagnostic computers found at dealerships and shops today. The avarage guy is just screwed trying to work on a 2007 whatever car without an interface computer and the propritary software to even reset the ECM after a simple repair. I got off on a tangent but just miss the good old days of common sense and simple testing to fix your car instead of the black box technology of today.

[tcrist]

ceslaw

Just a thought and I don't see it mentioned. Is it smoking from the exhaust at all. Do you see an oily film on the car after where the exhaust exits? Sounds to me like you are getting a lot of oil in the cylinder and it is trying to blow by the spark plug threads. If there is no oil trail from the valve cover to the spark plug, that would be where I think it is coming from. Could an oil ring be cracked or maybe someone did not rotate the rings correctly at assembly (so they are not lined up at the splits)? Hopefully it is none of things and maybe you could replace the valve seals on that cylinder and that will be it.

I new a guy that had a sprint car and he bought a used set of heads from RCR. They were told that they came off of Dale Sr's car. This was about 12 years ago. They put the heads on the car and fired it up and oil was just pooring out the exhaust. The found that the head was cracked in the intake cavity on #8 cylinder.

Terry

[patrickt]

When you put the vacuum gauge on your engine (manifold vacuum, not ported from the carb) post the results. Specifically the behavior of the needle, not just the numbers. For instance, if the needle appears to be reasonably steady around a certain number but then dives down several inches, then back to where it was originally hovering again, and does so in a rhythmic pattern. I've been a believer in the vacuum gauge as an initial diagnostic tool for a long time. Once you have a tool that is indicating a problem you can then take more "non-invasive" diagnostic steps to see if you can make the gauge read normally, even for just a few seconds. That will help you pinpoint the problem.

[ceslaw]

Thanks for all the input. This has proven to be a real education for me.

I am now the proud owner of a new compression gauge and I will post the results of the compression test once I have a chance to do it. Did not yet buy a vacuum gauge - that is the next project. I will report the details of how behaves when I get a chance.

I think Terry may have hit on a point that has been puzzeling me. If cylinder #2 is taking on so much oil, why is there no indication of buring oil in the exhaust? There is no appearance or aroma of burning oil whatsoever. There is no oily residue from the exahust. Had I not pulled the plugs I would have not had a clue that there was even a problem with plug #2.

I am really wondering if I have overestimated the oil consumption, since I was in the habit of toping it off the oil with a just a few ounces at a time rather than waiting for it to get a quart low. I am going to keep very accurate records of what is added from this point on.

I am still wondering if perhaps the rings have not fully seated - still have less than 2500 miles on the car.

But that puddle of oil around the base of plug #2 when I checked the new plugs last night still puzzles me.

Chuck

[MacGyver]

As you are already finding there are many possibilities. All you can do is use a logical process of elimination. Be carefull regarding the compression/leakdown test results. You can have good cylinder compression with bad oil rings. In some cases oil in the cylinder can actually raise the compression. You are wise to monitor the oil consumption as a baseline. Oil consumption doesn't always show up as residue at the tailpipe. The vacuum test is also very good advise. The oil on the spark plug threads is a big clue We all have a tendancy to think the worse at first. Start with simple than work you way down the diagnostic tree. You have a major puzzle on your hands that I believe will lead to removing the head. Let us know. You have all of us very curious..

Thanks, Matt