5.0L (1979-1995) MustangTechnical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.
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Here's a problem that is new to me. I changed my spark plugs yesterday and 7 of the plugs came out nice and dry with a slight tan tint. The 8th one from cylinder number 4 was black on one side of the electrode with a tar like residue on it. I am assuming that cylinder is running rich as it hadsometimes smelled like raw fuel during startup around cylinder 4. The injectors are 24lb Ford blue tops I had purchased new and have approximately 5,000 miles on them. I would appreciate any input.
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Could be a bad or weak plug. Check your wires also, ohm them out if necessary. Check your dist. cap for cracks or corroded terminals. Also could be a valve seal leaking into the cyl, or worn rings. Do a compression check and see if that cyl. is close to the same pressure as the others.Does the car smoke at all? This could be a symptom of seal or ring problems.
Here's where it becomes confusing to me. The engine is a relatively new GT40 crate motor (7,000 miles) and I have just done a tune up. That's when I found the unhappy plug. I am running a Pro M-80mm calibrated for the injectors and after having a few dog mass air meters, I can tell you this is the absolutely smoothest running meter I have had since stock. For some reason that particular cylinder is running rich as I am able to smell raw fuel at times right by the passenger side firewall (no. 4 cylinder). Has anyone ever had a bad injector and if so, please share the symptoms with me.
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