I have a 97 F250 7.5L gas engine that is giving me fits. Here's the history...
-Bought used about 5yrs ago($2k), previous work truck sold at auction with about 125k.
-Three years ago had a 'service engine' light come on while pulling camper and after having a mechanic check it, he thought maybe the catalytic converter was bad. Had a muffler shop cut it out and straight pipe it. Nobody knew what to do with the small pipe on the catalytic converter, so we left it cut off an unplugged. (please don't tell the air quality *****)
-Two years ago, noticed a slight miss and very poor fuel economy(worse than the normal "really bad" of a 460 v8). Had mechanic do a compression test and cyl2 was very low. Unplugged fuel injector to help with fuel economy, and truck has run fine ever since as a 402.5ci v7 engine.
-Last week the service engine light reappeared and the truck would chug and cut out just a couple of times, in the morning while hunting(mud, lots of it and water/snow) and it was colder outside about 30f. It ran all day just fine after that, but I noticed the day got warmer, about 50f.
-Tuesday morning headed to go hunting, but it was cold, 25f. The service light came on again and it ran poorly all morning. Came home early worried it would leave us on the mtn, so we had it scanned @ NAPA, and of course, it's an OBD-I connection and threw a DTC:90 code, which by all things I could find, this code doesn't exist. I changed fuel filter, air filter, spark plugs and wires, and pulled distributor cap and cleaned connections. It ran fine that afternoon, never missed a lick, running 50miles down the highway in 50f weather and low elevation 5kft.
-Wed morning took off for hunting, and again it was cold, 25f, and it ran fine for about 15miles, then threw the service light again and started missing again, and missed all day. Now it throws the code continuously and misses regularly. It does seem to run fine at 70miles an hour, and only misses a few times. It's really weird, and I can smell rich fuel exhaust and it back-fires now occassionally. It also runs fine for a while, (minutes) and when I really get my foot into it. Fuel economy is now very very poor.

Does anyone know of any sensors or anything I can check or replace that might be causing it to make an incorrect air/fuel ratio? Could the muffler being bad cause such a thing to happen? Any help anyone can give is greatly appreciated. Maybe it's just a dead truck now and ready for a rebuild?

 

Anyone? Anyone? Beuller?