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Here's the story. '89 240, 250K. Replaced timing belt & tensioner, belts. She runs great. No indication That I screwed up the timing. A few hundred miles later I take the emissions test in NYC. Pretty tough. Failed. HC was just a tiny bit over; .80 limit, I had .82. I'm assuming .82 is a tiny bit. CO low, as was NOx. So I replace the plugs. Failed to do research about reading them. As recalled they looked good. Cap & rotor looked good, the plug wires as well. Just cleaned them up. Then I poured in a can of Greased Lighting, injection cleaner into the tank full of regular gas I usually run. Figured I'd run it out and fill it with premium for the test. Well a funny thing happened while running out the regular gas with injection cleaner, 80 miles into it, I blew a plug in my header pipe. A perfectly round hole the size of a quarter. Located about a foot ahead of the cat and O2 sensor. It was loud and I probably gained about 10 or 12 horsepower. I drove it home and welded a plug over it. I guess the inj. cleaner did its job and gave me higher compression. I believe now, the placement of the hole in the stock header was for the O2 sensor in older models. So I ran out the gas, filled it with premium and took the test, and failed again with even higher HC and above the limit on the NOx. CO was low. So what is the chemisty here? When I filled with premium there was still a few gallons of reg w/inj cleaner. Would this affect the readings? The other thing is...could I have damaged the cat when the plug in the header blew? For the next test I'm replacing the cap, rotor, and plug wires, running out the gas again filling with premium. One other thing... after failing the first test I had a OBD reading of 231(I believe that was the code) lean or rich at cruise. 300 miles of driving, gas w/inj cleaner, the code has not returned. Thanks for your in-put...Mario
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