I haven't been on here in a while, but I'm back with a vengeance. Or with a problem. The past 2 weeks my truck has been throwing a check engine light, but only in short bursts. It will pop on, flick off, then sometimes continue flickering for a few minutes, sometimes it stays on a while, sometimes it won't come on for a whole trip. It also seems to run better once it warms up to op. temp. I ran codes engine on and off. Engine off I didn't get anything unusual. Engine running I got the HEGO lean code.

My truck runs rich as it is, and when the light comes on it runs even richer. You can smell it. So it's definitely not running lean. My first guess would be the o2 sensor. But I replaced it only about a year and a half ago. Unfortunately the warranty is only 12 months. My other thought is the Fuel Pressure Regulator, but I don't know that that's the problem either. So rather than throw money at it, I figured I'd do some research.

My problem seems similar to these 2 posts, but neither came up with an answer...

https://www.f150forum.com/f10/check-engine-hego-97216/

https://www.f150forum.com/f10/argh-oxygen-sensor-79966/

Anybody know what I can do to test and figure it out???

 

How many miles have you put on since you changed the O2 Sensor? They get lazy after about 60k. I'm at 106k and will be changing mine, since I run rich until I'm warmed up.

 

Maybe 20k, it wasn't driven very much, just work and back mostly. I havent pulled it out, but I may take it out and clean it with some carb cleaner or electric parts cleaner

 

Well yesterday I took the o2 sensor out and sprayed it good with some electronic parts cleaner and so far the light hasn't come back on. But it wasn't very dirty so we'll see if it stays off.

 

The light is back :/ I'm going to try installing the old sensor since I'm pretty sure I still have it. I replaced it by mileage but the old one wasn't throwing a code. So if the light stays off with the other sensor in, I guess I'll be buying another one of those.

 

Did you unplug the negative battery cable after changing the 02 Sensor? If not, do that for about 15-20 minutes and it will start a new reading instead of the old reading it was getting from the new 02 Sensor

 

Yea I left the battery unplugged yesterday day and cleaned the intake manifold, newer o2 sensor, and hooked it back up after it was running really lousy the day before. I got a code for bad ECT sensor, so I replaced the coolant temp sensor and the light went away for a few miles then started flickering again for the o2 sensor again. So I put the old sensor in and today I'm driving it with that to see what happens. I'll post back results

 

Just trying to rule out a bad sensor, but are you sure it's the right O2 Sensor for your model?

I'm not sure on how you would go about testing an O2, but if you find a way, do it, if not, return the sensor and let them know it was faulty.

 

The sensor was just over the 12 month warranty, so I can't return it. But the old one seems to be working. I cleaned it with electronic parts cleaner and put it back in. It's the original ford one with over 100k on it though, so I will replace it soon. But I drove all day today and the light came on once for about 2 seconds, but it was before the truck was warmed up and it was idling lousy because I hadn't reset the IAC. I reset the IAC and got the idle smooth again, and I haven't seen the light come on and the truck seems to be running leaner. It's a little rich smelling but this truck seems to always run a little bit rich.

I need to put a few more miles on it to be sure, but I think the o2 sensor was the culprit. A new one is 40 bucks, so if the old one seems to work I'll just grab a new one next paycheck and be done with it.

 

It's supposed to.