O2 sensor

[a_kelley]

So wife's truck was running hot, using coolant. Ok, shaved the head, new head gasket. No longer runs hot, but still getting low single digit mileage. Code present p0171, fuel system lean. It was running pig rich. Check fuel pressure with a (bad) gauge, shows 70psi(!). Come in today, gauge reading 20psi, with no pressure. Had started to drop tank & stopped, left filler hoses loose. Change gauges, shows 50 psi, a little high but ok. Unplug upstream o2 & reset trip computer & go for a ten mile drive, now showing 17mpg. I'm assuming coolant contaminated the o2 and caused it to read lean at stoich. I've not replaced it yet but getting 17 mpg is way better than 5mpg. Moral of story, if you're getting poor fuel economy, and you've got 250k on it, try unplugging the o2 to see if it's making it run rich. If it fixes it, you know what the issue is.

 

[a_kelley]

Oh I did reset the fuel adaptive values after doing the head and after unplugging o2. I have seen the adaptives screw up the driveability on several different makes/models after repairs, even though the problem was fixed, the learned values screwed up the driveability. (Clogged cats, head gaskets, o2s, etc - anything that affects the computers perception of fueling can make it"learn" to cope with it, and after repair, it needs a adapt reset) that's an important part. Just unhooking the battery will not reset the adaptive values. Even on 91-95 Jeep products with the sbec.