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#2 dry fouls plugs, why?

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Old 07-11-2018, 09:41 AM
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kael
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Default #2 dry fouls plugs, why?

'87 w/L98

Not sure what's the problem here. A new plug in #2 cylinder will run fine for about 100 miles, then start missing and be fouled on removal, oily. Repeat, same thing. Chasing this, I've pulled the plug after 50 miles, before missing starts. At that time, the plug is black, DRY black. That indicates rich mixture, right? What would cause that?

Currently, I think it's worn rings causing low compression, meaning engine rebuild. I'd be pissed if after rebuild this still happened, already had heads and valves serviced, valve seals replaced and all other kinds of stuff except a rebuild.
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Old 07-11-2018, 09:51 AM
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cuisinartvette
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Wondering if you got a leaky injector
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Old 07-11-2018, 10:21 AM
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Kevova
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50 to 100 miles wow. Leaking or fouled injector. Pressure test with injectors inch above intake look for drip. Swap injectors to verify injector or cylinder problem. On tpi absolutely sucks might just replace injectors. Is engine losing oil? Retorque intake manifold. Make sure #2 intake valve seal is in place. Does exhaust smoke? Rings not sealing I would expect some smoking. Test spark with tester at #2 make sure it's not weak. Wire should ohm less than 10k.
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Old 07-11-2018, 11:00 AM
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ddahlgren
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How old cap rotor wires and injectors? My 91 is 26 years old.. LOL This stuff does not last forever.. Do a compression test on the cylinder or leak down on it.
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Old 07-12-2018, 10:30 PM
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kael
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I've been chasing this for last 2 years.

Out of order:
Replaced plugs.
Replaced plug wires.
Replaced distributor coil, cap.
Replaced injectors (no change, still #2).
Reinstalled inspected heads with 3 new valves.
Replaced valve seals.
Reinstalled intake manifold twice.
Replaced EGR valve.
Replaced fuel regulator.
Replaced some vacuum hoses.
Replaced cold start oring twice (joke, see https://www.corvetteforum.com/forums...104-oring.html)
Probably some other items I'm forgetting.

No smoke out of exhaust, not sure if going 60+MPH.
Exhaust doesn't smell weird.
After the plug fouls, I can tell when these days, oil is lost, up to a quart in 50 miles. New plug, when not foul, no oil lost.
No oil drips.
Tried different spark plug wires.
Spark tested, looks good.
All the other plugs look fine, replaced them all twice.
Fuel pressure is good, replaced fuel pump too.

Last edited by kael; 07-12-2018 at 10:32 PM.
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Old 07-12-2018, 10:47 PM
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Kevova
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Compression and leak down test. Replace valve seals #2. When cylinder is firing there is more heat. Parts expand preventing oil loss. Fouled cylinders cooler allows oil loss. Pita but pull head and have it checked
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Old 07-12-2018, 11:29 PM
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ddahlgren
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If an 87 has a flat tappet cam I would be checking valve lift on # 2and compare it to another cylinder. Might have a lobe gone flat and my guess an exhaust lobe.
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Old 07-13-2018, 09:18 AM
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PatternDayTrader
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Install the hottest plug you can buy. This might get you by.
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Old 07-13-2018, 01:08 PM
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383vett
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As 2 others have mentioned, do a leakdown test. It'll show you the health or sickness of all the cylinders. Why would you replace all those parts trying to figure out the problem when a simple test with give you a diagnosis?
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Old 07-13-2018, 04:54 PM
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B757captain
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Many years ago I had a similar problem. Turned out to be that the expander on the oil ring was broken, allowing excess oil into the combustion chamber. Neither compression test nor leak down showed the problem, engine ran great right up to fouling the plug. No symptoms other than small oil loss over time. I finally pulled the head and the offending piston to find the broken expander. No damage to the cylinder wall so I replaced the oil control rings on that piston. Ran great after that.

If you have access to to a borescope (can get pretty cheap on Amazon) check the cylinder through the spark plug hole and compare with its neighbors. I seem to remember that the offending cylinder and piston were too clean (looked washed down) compared to the adjacent normal ones.
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Old 07-13-2018, 05:37 PM
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383vett
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Originally Posted by B757captain View Post

If you have access to to a borescope (can get pretty cheap on Amazon) check the cylinder through the spark plug hole and compare with its neighbors. I seem to remember that the offending cylinder and piston were too clean (looked washed down) compared to the adjacent normal ones.
Just wondering, if oil is getting past the rings due to a bad oil ring, how can that cylinder look clean? Are you sure you aren't confusing this with another situation where you may have had coolant in the combustion chamber?

Last edited by 383vett; 07-13-2018 at 05:37 PM.
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Old 07-13-2018, 05:40 PM
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ddahlgren
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Originally Posted by B757captain View Post
Many years ago I had a similar problem. Turned out to be that the expander on the oil ring was broken, allowing excess oil into the combustion chamber. Neither compression test nor leak down showed the problem, engine ran great right up to fouling the plug. No symptoms other than small oil loss over time. I finally pulled the head and the offending piston to find the broken expander. No damage to the cylinder wall so I replaced the oil control rings on that piston. Ran great after that.

If you have access to to a borescope (can get pretty cheap on Amazon) check the cylinder through the spark plug hole and compare with its neighbors. I seem to remember that the offending cylinder and piston were too clean (looked washed down) compared to the adjacent normal ones.
Right or wrong said it was fouled dry typical from being way too rich. Loss of oil control will make it smoke and plug will be wet and oil fouled..
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Old 07-13-2018, 08:59 PM
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ihatebarkingdogs
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Someone mentioned a possibly flat cam lobe. I agree. A significant loss of lift on an exhaust valve will cause incomplete exhaust scavenging, and inefficient combustion. (think "too much EGR"), The plug will look black, but dry. Compare the lift of #2's exhaust valve to its neighbors. Neither a leakdown nor a compression test will uncover a flat cam lobe. It WILL show on a vacuum gauge at idle as a single downward spike when the affected cylinder's intake valve opens and the pent-up pressure rushes back into the intake manifold forcing the vacuum to momentarily "drop".

Last edited by ihatebarkingdogs; 07-13-2018 at 09:05 PM.
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Old 07-14-2018, 03:43 AM
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Mentioned that in post #7 a very cheap easy check.
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Old 07-14-2018, 09:57 AM
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kael
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Originally Posted by ddahlgren View Post
Mentioned that in post #7 a very cheap easy check.
If that is the problem, would there be dirty exhaust back to the EGR valve? Both times I had the intake manifold out, the EGR passage was black powder, I don't know if that's due to foul or the lift issue you mentioned.

Damn, do I want to know how much a new shaft is?



Oh, to some others, who said I didn't do compression and leak down tests? An obvious result would have been great.
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Old 07-14-2018, 10:47 AM
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It will soot an intake manifold so I suppose it would the EGR too. Just pull the valve cover and look.
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Old 07-14-2018, 10:58 AM
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dont think #2 feeds egr. egr is black yes.

not a wiped crank, a wiped cam. cheap.

grab/borrow the vac gauge and see if the needle has a down spike like dogs and #7 said.

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Old 07-14-2018, 10:34 PM
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Originally Posted by VikingTrad3r View Post
dont think #2 feeds egr. egr is black yes.

not a wiped crank, a wiped cam. cheap.

grab/borrow the vac gauge and see if the needle has a down spike like dogs and #7 said.

Uh, no coffee or a late late Friday night?
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