Only 1 plug fouls...why?
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Only 1 plug fouls...why?
I have 96 ranger 4.0 with 160K miles and it ran fine till about a year ago--started with sporatic miss under load then got worse and worse. I replaced the plugs-wires and coil pack and problem went away only to come back after about 1500 miles. I found the front plug on the driver's bank fouled so I replaced it and it ran fine. Today it started it again so I checked fuel pressure (30#) and checked codes.
Showed a cylinder 3 misfire. I pulled what I think is the #3 plug (rear on passenger bank) and the plug looks great. I go to the front plug on the driver's side and it is fouled--I replace it and back to normal.
What is going on here?
I checked compression and it is uniform..
-burnt valve??
-bad injector??
Thanks for your help
michael
Showed a cylinder 3 misfire. I pulled what I think is the #3 plug (rear on passenger bank) and the plug looks great. I go to the front plug on the driver's side and it is fouled--I replace it and back to normal.
What is going on here?
I checked compression and it is uniform..
-burnt valve??
-bad injector??
Thanks for your help
michael
Posting Guru
Joined: Nov 2003
Posts: 2,107
Likes: 3
From: California Desert
It's possible that the valve seal for that cylinder has worn out and is letting a bit of oil in. What color is the fouling? If it's white then it's from oil being burnt. If it's black and wet it's from too much gas.
Post Fiend
Joined: Feb 2003
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From: Eastern WA
Ummm, need more info on this one before moving forward. How is it fouled; carbon or oil? What were the results of the compression test? Is it using coolant? Is it using oil? BTW, white = running very hot; oil consumption = black, slimy a bit to excessive, and with flakey deposits. Excessive oil may show as such on the plug. Also, a burnt valve can be detected during a compression test. If it's a burnt exhaust valve, you can also hear it in the exhaust (assuming a normal muffler is on the truck).
Last edited by CowboyBilly9Mile; Dec 8, 2004 at 07:44 PM.
Cargo Master
Joined: Nov 2004
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From: Friendswood, Texas
Single Fouling Plug
I have this problem with my 93 F-150 with a 302. It has done this for five or six years now. I have attributed this to a bad valve seal. Last three times I have replaced plugs it was because of a miss and each time it was the rear plug on the driver's side. Replace it and it runs fine. I've always figured that replacing plugs every year ot two was easier than tearing down the engine so I have never bothered to find the real source of the problem.
New User
Joined: Dec 2004
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i just had a problem with my 98 ranger, i have 77000 on it, and i kept burning my plugs, the whole electrode would dissappear! come to find out, my head gasket is bad, and i have to do a big repair on the engine now. same symptoms you had, except my compression numbers were off quite a bit.
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Laughing Gas
Joined: Jul 2004
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A heavy brown/reddish deposit on a plug in one cylinder only is coolant burning in the cylinder. Wonder how I know this??? 
All kidding aside, I just stripped down my 86 SVO last week for a blown head gasket that was letting a small amount of coolant in the cylinder, and the entire cylinder (valves, combustion chamber, piston tops, plug) were all coated with a brown/reddish deposit from where the head gasket partially delaminated and blew out part of the steel ring around the #2 cylinder, allowing coolant to seep in.
Another possibility could be a fuel additive, but usually that will discolor all the plugs, and not just one.
All kidding aside, I just stripped down my 86 SVO last week for a blown head gasket that was letting a small amount of coolant in the cylinder, and the entire cylinder (valves, combustion chamber, piston tops, plug) were all coated with a brown/reddish deposit from where the head gasket partially delaminated and blew out part of the steel ring around the #2 cylinder, allowing coolant to seep in.
Another possibility could be a fuel additive, but usually that will discolor all the plugs, and not just one.
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