spark plug reading
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Tuned
Joined: Apr 2001
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From: Newbury NH
spark plug reading
92 4.0,180,000, no idea when they were changed last. pulled a trailer the other day and had a skip under load,back off the gas and the skip went away. so i bought ne plugs and these are the old ones. pass. side ones are on the left. any ides what going on with the 4/5th ones?? looks like oil on one.
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Logistics Pro
Joined: Jan 2002
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From: suburban atlanta
The edge of the center electrodes on all of them look rounded to me. I think they needed to be replaced. The passenger side sure looks as if they all are working the same. The drivers side, not so much. The first two on the drivers side have deposits, which may have taken a long time to form, the last looks the same as the passenger side. If it runs well, I'd leave it alone unless the mpg is not up to expectations. You may have slightly leaky injectors on 4 & 5, causing a little bit richer mix than the other four, leaving the deposits. Or it could be slight leakage past the valve stems. You certainly could check compression and compare to the plugs.
Other posters may be able to read plugs better than I. The oil on #5 is external, from a rocker arm cover that is slightly leaking or from spillage when oil changes were performed. It is not internal oil from the combustion chamber.
tom
Other posters may be able to read plugs better than I. The oil on #5 is external, from a rocker arm cover that is slightly leaking or from spillage when oil changes were performed. It is not internal oil from the combustion chamber.
tom
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Joined: Jan 2011
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From: Connecticut
Crusty old plugs
From the reading I've done, crusty buildup on the plug is an indicator of oil during combustion. Given the build-up you have, it could have been fouled to the extent it gave you the misfire (can you/did you check for a code?) especially under load.
Kevin
Kevin
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From: Connecticut
Keep the crust for the pumpkin pie
I took a look at the Haynes manual - has a section in there with images of different plug conditions. Says it could be oil or fuel additives. If oil, could be bad valve guide seals.
PS - do you own a Tbolt?
PS - do you own a Tbolt?
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Tuned
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From: Newbury NH
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From: SW Va
I like tomw & Racksters ideas & agree the old plugs look worn & probably have out of spec spark gap too.
Our 4.0L is specified to use 5w-30 & the new fine wire iridium enhanced center electrode, with platinum pad ground sidewire type plugs, so if you up graded to them you'll likely notice faster year round starts.
If you think you may have valve stem leaks on #4, maybe consider trying a "high mileage" crank case lube who's recipe has extra seal conditioning ads & detergents, along with a viscosity index thats typically on the higher side of spec, that might help tweak things some.
Maybe also consider a 20 oz dose of Chevrons Techron Concentrate Plus in the tank at the pump, before filling up, so you get good mixing. This with Chevron, Texaco, Caltex, or other pump gas with Techron already in it, will raise the treat rate 10X above pump gas alone, so it'll likely be able to tidy up #4 & 5 cylinders & fuel injectors in one tank. If you don't have any of those fuels, try Shell, as they now have a PEA based fuel additive like Techron. Advance Auto has Techron on a by one get one this month.
More thoughts for consideration, let us know how it goes.
Our 4.0L is specified to use 5w-30 & the new fine wire iridium enhanced center electrode, with platinum pad ground sidewire type plugs, so if you up graded to them you'll likely notice faster year round starts.
If you think you may have valve stem leaks on #4, maybe consider trying a "high mileage" crank case lube who's recipe has extra seal conditioning ads & detergents, along with a viscosity index thats typically on the higher side of spec, that might help tweak things some.
Maybe also consider a 20 oz dose of Chevrons Techron Concentrate Plus in the tank at the pump, before filling up, so you get good mixing. This with Chevron, Texaco, Caltex, or other pump gas with Techron already in it, will raise the treat rate 10X above pump gas alone, so it'll likely be able to tidy up #4 & 5 cylinders & fuel injectors in one tank. If you don't have any of those fuels, try Shell, as they now have a PEA based fuel additive like Techron. Advance Auto has Techron on a by one get one this month.
More thoughts for consideration, let us know how it goes.
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