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I cut the exhaust off of my 94 F-150 XL 4.9L M5OD 4x4 just before the first cat. I left the O2 sensor in place so the engine can still run right. I also cut off the air pipe that runs down between the cats right at the exhaust pipe. I intend on installing a Y pipe, and single tube exhaust. I know the air pipe being cut off is the reason my CEL is coming on, but the question is why? From what I understand, the air pump just takes the recirculated gasses and pumps them into the exhaust tube to be transformed by the catalist in the catalitic converters. I have been driving it around for about a week, and my CEL didn't come on at all. I drove for almost 60 miles on the highway today, and then, all the sudden it came on for a few seconds, went away, and then came back on briefly, and then went back out. It wasn't flashing a code, it was too "random" for a code to be flashing. Anyways, give me your thoughs, suggestions, tips, or guesses. Thanks in advance.
if it matters, the truck has 202,000+ miles, a 4" lift, and 33"x12.5" R15 Micky Thompson Claws.
I had a similar problem after I did the same thing. Turns out I had forgotten to install the O2 sensor. if you didn't remove it check the electrical connection. When was the last time the O2 was changed? should do it about every 100k km or so.
yeah, the 02 sensor is factory equipment (202,000+ miles). It was loose when I cut the pipe off. Not really worried about any of that, as the engine is coming out eventually. I want to know why it came on. Oh well.
You should pull the codes to see why the computer is turning on the check engine light. There are some basic instructions on www.fordfuelinjection.com that should get you started.