I have a 1989 F-250 4x4 with a 460, 5 spd. Now until recently I was getting respectable fuel mileage. On the interstate it was pulling around 16.5, while in town and short trips it was around 12-13.5 !
I recently put on a catback dual exhaust, and then put in new plugs, distributor cap and rotor. I also installed a K& N hi-flo air filter since the old paper cartridge one was due to be changed, and suddenly my fuel mileage plummeted to just barely over 10mpg. Let me add that when I put on the exhaust, miy fuel mileage increased. This truck has 67000 original on it. I have looked for external leaks, found none I have checked for a vacumn line being off, also found none. I put on a new fuel filter, but nothing seems to be the culprit.
I have a code reader and I have pulled a 33 out of it, but I took it to the local ford garage. Had them do a onceover on it, and they claimed they found no codes. My check engine light has never come on and it does work (coming on briefly when the ignition is turned on).
The people at the ford garage told me that my check engine light should come on whenever a code is stored. But that as I stated earlier has never happened. And yet there are times when I have power and then have none.
I'm now wondering if my trucks brain box is malfunctioning.
Any info would be greatly appreciated.