Fouling #1 plug - HELP!

thinkfaster

Member
Jun 15, 2007
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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?

1646344985822.png
 
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dcm0123

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Mar 11, 2017
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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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dcm0123

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Mar 11, 2017
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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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Mustang5L5

Put lubricant all over the balls
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Feb 18, 2001
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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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KRUISR

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Apr 16, 2015
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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).
 

dcm0123

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Mar 11, 2017
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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).

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

1646611770796.png
 

Bullitt347

I have been doing it wrong this whole time
15 Year Member
Mar 23, 2007
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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.
 

KRUISR

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Apr 16, 2015
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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.
 
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Bullitt347

I have been doing it wrong this whole time
15 Year Member
Mar 23, 2007
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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.
 

thinkfaster

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Jun 15, 2007
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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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manicmechanic007

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Sep 26, 2017
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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?