i have had this problem since i bought my truck about a year ago and i cant figure it out. if i drive a constant speed of 55 or faster for very long the check engine light flashes a code and it is the O2 sensor. all i have to do is let off the gas pedal and step back on the gas again and it goes out. a few minutes later it is on again and so on and so on and so on. i pulled out the old O2 sensor last winter and the thing was pretty distorted and twisted, (i never seen anything like this before). i replaced it with a brand new one for my truck. and it has not helped at all. same problem nothing changed. im only getting 14-15 miles per gallon. truck runs smooth, very dependable. plugs look good and has a recent tune up. im trying to figure out the O2 sensor hoping this is my problem with the gas mileage. my truck is a 86 rte 4wd with automatic. i realize i am only suppose to get 20 mpg with this setup but as i said im only getting 14-15 and that is all interstate driving and driving 65-70 mph and not romping on the gas at all. any suggestions.

im at the point now that i would be willing to trade for a 4wd toyota without the turbo just to get some gas mileage, because im driving about 350 miles a week, and with the price of gas it it killing me

You might try pulling you egr off and cleaning it, they can get plugged with carbon and not work properly.

How are you getting an error code as you are driving down the road?

the check engine light comes on while im driving. when i get home i pull the codes and the only thing i get is for the O2 sensor

Well, a couple things come to mind. If this is the 86 in your sig, I'm not as sure, but I know on the 96+ OBDII systems a flashing light means a misfire.

The other thing you might consider replacing is your thermostat. If it's stuck open, your truck will not get hot enough, and the O2 sensor will complain.

yes this is the same truck as in my signature. im pretty sure the thermostat is working good. it heats up and cool down normally. i also checked the egr as mentioned earlier in a post. it seemed to be working fine. i just changed the head last week with one that had been rebuilt from a dealer. but it was doing this same thing before i changed the head.

There are tests you can do on the O2 sensor in the FSM so you can be positive it's OK.

I'd also check the wiring between the O2 sensor & the computer for continuity. A broken wire will look like a bad sensor to the ECU.

Dave

good idea, ill try that in the morning