Fouling #1 plug - HELP!

thinkfaster

15 Year Member
Jun 15, 2007
27
38
23
Houston, TX
After searching the interwebs, asking a few friends, and trying almost everything I could think of, I still haven't been able to fix my problem. Here's the rundown:

I've got an 1989 5.0/T-5 w/75k actual miles that sat for 7+ years before I bought it. It briefly smokes upon acceleration AFTER a high RPM deceleration in gear (high vacuum condition) ONLY. No idle smoke, start-up smoke, etc... #1 spark plug is black/wet/nearly fouled after 10 mikes of driving. All other plugs look normal. Car starts, runs, and idles ok with a slight random misfire at times, as you’d expect with a wet/black #1 plug.

Here’s what I've tried so far to remedy the situation:
  • Replaced spark plugs
  • Compression tested cold/dry 116-124psi across the board
  • Disconnected PCV system (no change)
  • Replaced PCV, grommet, & screen
  • Replaced all valve seals with new Viton seals
  • Swapped injectors around & rechecked plugs
  • Installed a platinum iridium plug in #1 to limp by for more diagnostics
  • Endoscope confirmed crosshatching still present in #1 cyl, no cylinder damage, & no piston damage
  • Added Marvel Mystery oil to engine oil
  • Added Lucas HD oil stabilizer to engine oil
My last two guesses at this point are #1 oil control ring is stuck/broken or lower intake manifold gasket is leaking. Anything else you guys can think of before I swap the lower intake manifold gasket?

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Have you replaced the wires, cap and rotor?

I would spray carb cleaner around the injector and intake manifold gasket while idling. A change in engine speed is an indication of an air leak.

If it is not hard to pull off the valve cover I would do it and see if there is less movement on one the of the valves on that cyclinder which would be an indication of a bad lobe on the cam.
 
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Another thought- Did you verify the firing order? Do you have the HO cam or the standard cam in it? (I believe this changes firing order).

I am not sure the spark plug is oil fouled. If not oil fouled then would not be a ring issue.
 
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Does compression rise at when you perform the test dry, and then add oil to the cylinder? You might need to compare #1 to another cylinder to see how the introduction of oil changed the compression numbers.

Intake gasket leak likely wouldn’t cause your issue. You can try a smoke test to see if you see any visible smoke around #1.
 
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Where does your PCV valve connect to the upper intake. Usually it connects at the back of the upper intake (by cylinder 7 and 8), but could be connected to the fitting at the front instead. If connected at the front only, you could be sucking in the oil vapour and introducing oil through the intake (ask me how I know - had same issue with cylinder 8).
 
Where does your PCV valve connect to the upper intake. Usually it connects at the back of the upper intake (by cylinder 7 and 8), but could be connected to the fitting at the front instead. If connected at the front only, you could be sucking in the oil vapour and introducing oil through the intake (ask me how I know - had same issue with cylinder 8).

That is a good point. Do not forget the breather element below the PVC valve to keep oil from splashing into it.

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Bullet point 7 in post #1

But obviously it has fouled too.
That was guaranteed to happen. He used a plug that requires less spark energy (weaker spark) and one that is a much colder heat range. He should have tried a copper plug, and not Champion, and one that was at least as hot as the other 7 plugs if not a range hotter.
 
True but if his plug is being fouled with oil it doesn't matter what plug he puts in it will get fouled again. If the fouling is fuel based soot then you are correct in that the wrong plug will cause some of the fouling.

When I was fighting a plug fouling with oil I carried an old plug to limp home and then would clean the fouled plug with some brake cleaner to get the oil off.
 
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True but if his plug is being fouled with oil it doesn't matter what plug he puts in it will get fouled again. If the fouling is fuel based soot then you are correct in that the wrong plug will cause some of the fouling.

When I was fighting a plug fouling with oil I carried an old plug to limp home and then would clean the fouled plug with some brake cleaner to get the oil off.
It could just be a bad plug. Champions are notorious for going bad, even right out of the box. It is why I will not use them.
Putting a weaker, colder plug in to diag a fouling issue is just asking for trouble.
 
Shoot! You guys loaded me up with questions, thanks! I’ll address all at once:

dcm0123:
  • Yes, new cap/rotor/wires.
  • I suspect the intake lower intake gasket leak is internal, rather than external.
  • Good point about cam lobe, I hadn’t thought about that. However, everything looked pretty normal when torqueing rockers after reassembling/rotating post valve stem seal replacement.
  • Firing order was checked & rechecked, HO cam.
  • Plug is definitely oil fouled; looks, smells, & feels like oil.

Mustang5L5:
  • I have not tried a wet compression test yet. Good idea on the smoke test!

KRUISR/Bullitt347/General karthief:

PCV is in the back, whole system (screen included) was replaced, no change as stated.

I believe I bought the platinum/iridium plug with the same heat range and read somewhere that due to the hotter burn it was less susceptible to fouling, but I’m no expert. All plugs were replaced with Autolite coppers; #1 fouled in about 10 miles as stated. That’s when I replaced #1 with platinum/iridium. The plugs pictured were the ones in there when I bought the car, looks like the PO tried it too but with the wrong heat range plug.
 
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So it runs great for 10 miles then fouls #1
I am all for checking the valve stem seals on that cylinder (loose guide etc.)
All the above posts are great
Good luck
It might just be over fueling #1 with a bad injector or even a bad plug wire, and once it fouls you are seeing some oil?
 
I am having the same issue with plug #8, fouls after 20 minutes of driving.
  1. I have replaced the PCV and ran the breather through the sonic cleaner for a good hour.
  2. I have also replaced the valve seals on #8.
  3. I poked a coat hanger down the oil return, does not seem clogged.
  4. I also noticed that when I pull the upper intake, the gasket between the upper and lower intake has soaked up some oil on the rear ports. Really seems like PCV issue to me.


    Was going to try a catch can to see if this makes it go away.
    KRUISR you had this same issue? What was the resolution?
 
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I did a version of a catch can - I used an air system oil separator inline between the PCV and intake manifold connection. It worked to stop the fouling. The next spring I picked up a used GT40 headed long block and did a swap (previous engine was the stock original with 250K km).

My original motor had great compression but would blow blue smoke under hard acceleration - that's why I looked for a replacement. I had replaced the valve seals on it as well, but believe my exhaust valve seals were either not installed right or just crappy parts.
 
I did a version of a catch can - I used an air system oil separator inline between the PCV and intake manifold connection. It worked to stop the fouling. The next spring I picked up a used GT40 headed long block and did a swap (previous engine was the stock original with 250K km).

My original motor had great compression but would blow blue smoke under hard acceleration - that's why I looked for a replacement. I had replaced the valve seals on it as well, but believe my exhaust valve seals were either not installed right or just crappy parts.
Thanks for the response. So excessive blowby? I'm thinking pull the motor in the fall and re-ring/refresh it. I'm doing a test now to see how many miles I can get out of it before I need to swap the plug. May just live with it for the summer, plenty of other things to drive.
 
I don't think mine was from the rings, I think mine was the valve seals.

When I did my compression test I was 140+ on all cylinders - if memory serves
 
I don't think mine was from the rings, I think mine was the valve seals.

When I did my compression test I was 140+ on all cylinders - if memory serves
Mine is also 140+ on all of the cylinders. I wonder if I just replace all of the seals? I only did #8 because I thought that was the problem. Might be worth a shot, easier than yanking the motor. As I said, I think it's blowby since the gasket between the upper and lower is saturated with oil on the back ports. I think, and I could be wrong, the value guide seals would not cause blowby? A catch can would determine if it's coming from the PCV for sure, might be the first next course of action.
 
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