Alright guys, I picked up a 97 F-150 4x4 yesterday for $1000 with 300k miles on the clock. I had to drive it 3 hours to my parents house, and the truck had a misfire unless it was romped on or when ya let off and coasted. The guy suspected electronics at first, changed all the plugs and o2 sensors and it did nothing. So he changed the TPS and IAC and nothing. So he changed the vacuum lines and nothing. So he gave up and I bought it. It would hit on all eight if you'd give it, but miss when cruising... when we started going. Thing started spark knocking like crazy, so I told him to give 'er till she blows up. 3 hour drive and she didn't blow up and it ain't spark knocking anymore but it's also not clearing up when its revved. It's not smoking at all (out of some sort of magic), doesn't burn oil or coolant and doesn't leak any either of each. I haven't had a chance to scan it and will do this coming weekend (I live an hour and a half from my parents and can't have 2 vehicles here), but what does everyone else think is wrong?
Oh, previous owner scanned it and got code P0174 (system lean bank 2 sensor 1). I sprayed intake with starting fluid on bank 2 and no rev up or anything.
Alright made some progress. Previous owner never tightened spark plug number 6 and it wasn't firing. This truck doesn't have coil over plug, it has waste spark coil packs. Tightened the plug back up and it runs good, random misfire still, but runs good... until it gets warm. Hittin on 7 cylinders now when it's warm. Any ideas?
Edit: Was throwing P0174 before tightening the plug up. Now it's not throwing any codes.
More progress! Truck ran awesome today... for about 2 minutes. Then the misfire showed its ugly face again. Did a little research, found plug #4 is prone to misfire issues, so I pulled the boot off and whaddaya know! Oil in the plug hole from the valve cover! Cleaned it up a little, but didn't have an air hose handy to blow the hole out. There's always tomorrow to break out the ol' compressor and give it a shot! Truck seemed to have only a random miss now, but very often at warm.
I ended up changing an injector because it was pluggin up randomly and also changing plugs because the previous owner skipped the back two plugs on the passenger's side and the very back plug on the driver's side. Runs awesome now!
Edit: It has an intermittent miss at idle and cruising because I have one plug wire that's ready to poop out.
When I did a power balance test after changing plugs, I found #8 wouldn't contribute at all when you'd run it after a while (and it would misfire only there) so I swapped it out and it cleared it all up. Multimeter will only tell you if it's electronically within specification.
Edit: There was no misfire code for some reason because it would only plug up sometimes. I cleaned out the fuel rail when I changed it, too.