Plug number 1 fouls regularly... is it an injector issue?

Asked by Dec 26, 2010 at 01:29 AM about the 2002 Mazda Tribute LX V6

Question type: Maintenance & Repair

No. 1 plug continues to foul while other plugs stay clean. Is this an injector issue, cylinder, or valve issue? What is the best way to prove this out?
Thank you!

5 Answers


sounds more like a piston ring issue. Or, more precisely, an oil control ring! sorry!


Check your plug against the plug chart at Admittedly these are rather extreme examples but you can find an idea of where to look for the cause of your problem. An oily plug would imply oil is leaking into the cylinder from somewhere (either via the piston or a valve stem). If it's the oil ring on the piston you're in for a nice job, you're best off replacing the piston rings in the engine, which means pretty much an entire teardown. If on the other hand it's a valve stem seal, it's just a case of a bit of headwork. I'd recommend replacing the seals on all the valves or you'd be taking the head apart every few months to replace the next seal to start leaking.


I might think a injector would be the fault Have you checked the spark plug lead that its not breaking down under load other than electrical with the current to that particular plug I would get a compression test its possible that a piston ring is broken


actually it can be either faultu ignition system or a bad valve. u really need to get it checked thoroughly before u can reach to a conclusion.


if the plug is fouling with gasoline, I'd start thinking along the lines of Fuel Injector(s) or fuel pressure regulator....

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