Since I've owned my truck (96 f150 xl 2wd auto) I've had these codes, among others and have fixed them all but these two. I'm still getting a rough idle and lower than average fuel mileage
​ive had a shop check for vacuum leaks and couldn't find any, I've sprayed everything with carb cleaner and can't find any.
ive replaced pretty much all the vacuum lines, pcv valves, just replaced the fuel filter and pump... Still getting these 2 codes.

I've been told it could be a ground? Does anyone have any ideas ? I'm all out of things to try.

 

Also has a new maf and egr valve

 

The only other thing I could think of would be the injectors

 

How do I test them? I was thinking for?

 

What engine?

How old are the oxygen sensors?

I recommend getting an OBDII adapter that links your phone (assuming you have a smart phone, if not, i-pad maybe?) to the truck's PCM so you can b use something like TorquePro (a $5 app that's well worth it). You can watch the oxygen sensors switch rich/lean and actually graph their voltage over time. For an OBDII equipped vehicle this is a great tool.

By being able to watch the oxygen sensors voltages, you can determine if it is reading lean all the time (probably bad sensors) or only under hard load (weak fuel pressure or clogged injector(s).

 

It's the 4.9. whats the adpatper called? I just bought a scanguage 2 but I don't think that monitors the injectors?
It shows 6 codes though. 0171, 0174, 0171, 0174, 0171, 0174.

Could that be o2 sensors then since there's 3 of them?

 

Anyone else?

 

how long have you owned the truck ?
how old are the oxygen sensors ?
did you bring the engine up to operating temperature before pulling codes ?

 

I've had it about 7-8 months. The top 2 sensors look newish, previous owner said he had replaced them. The one at the cat looks original... And hard to get to.
Yes, cleared them and the same 6 came back on today

 

Have you googled those codes? Turns out they're the same 2 I could never track down on my 96 4.9L in the 100k miles I owned it. There seems to be much more info readily available now regarding them.

Curious about your fuel mileage though because even with those codes ever present, I was thrilled to get 15mpg locally and if I remember right, a little better on some cross country trips.

 

I'm not sure of the brand. It's an OBDII adapter, generically referred to as an Elm327 adapter. If you use an iphone you'll want a wifi style adapter, android uses bluetooth. I got mine on amazon a couple years ago for something like $15 shipped.

The 3rd oxygen sensor won't change how the truck runs, it simply monitors the function of the catalyst and will trigger it's own unique code.

Your lean codes are telling you that either the truck actually runs lean (fuel delivery issue or vacuum leak), or the detection system (the front two oxygen sensors) are giving false readings.

 

Before I changed my fuel pump, hoping that was the problem.. it didn't want to start good, even worse after it was hot.. that went away after fuel pump and egr.. but I was getting about 12. I drove it 212 miles this past weekend, helping a friend move.. so I had a trailer behind me some, or the bed loaded down, going down very hilly highways and got 15.1-15.8mpg. I'm going to see what she's getting this week going to work on flatter roads.

It makes me want to sell the truck, not being able to solve this. I ordered the Bluetooth adapter and got the torque pro app. It'll be here tomorrow.

 

Will the app tell me if it's the o2 sensors ? I'm pretty sure the previous owner put in cheap eBay sensors. The truck starts better after replacing the fuel pump but still idles rough. Doesn't run bad under load at all. Just shakes at idle

 

All,
I have the same issue on 97 F3507.5l Changed Intake gasket small leak there, Changed all vacuum lines some rotted out elbows, changed header gaskets, changed both upstream o2 sensors still had the codes. Next checked fuel pump pressures 2 tanks both were good and last but not least changed out the injectors trying to solve LTFT high numbers @ 16 to 18. Still no luck also where else to look? Looks as if you are down to injectors you were thinking about changing I would hold on they are expensive.

 

The app won't tell you the sensors are bad explicitly. It will, however, allow you to graph the voltage of the sensors.

(Maybe you know this already) As an engine runs, it does not maintain proper air/fuel ratio (AFR) constantly. Rather, it runs lean, the oxygen sensors tell the power train control module (PCM- aka ECU) that its running lean, PCM adds too much fuel, engine runs rich, oxygen sensors tell PCM it is rich, PCM trims fuel, and this cycle goes on the entire time the engine runs (except a few special cases (open-loop operation) like wide open throttle, it tends to just dump tons of fuel in those conditions). On a long term average, the engine runs just where the PCM wants to in terms of AFR.

The oxygen sensors read over 0.45V when rich & under 0.45V when lean. If the sensors are OK, you should see a sine wave type signal when you plot oxygen sensor voltage against time. The voltages should have low's of ~0.1V and highs up around 0.9V. Under heavy acceleration the oxygen sensors should read high voltage, without switching (mine are up around 0.85V-0.9V). Here's a good read if interested:What the Home Mechanic Needs to Know about O2 Sensors

More specifically for your situation (possibly, anyway)... At idle and steady state driving (closed loop PCM operation) you should see the sensors switch rich/lean often. If at idle, the sensors don't cycle or tend more towards lean, I'd bet the sensors are bad, so the PCM believes the engine is lean & adds fuel, actually making it run rich, and causing the rough idle.

I had the same code as you, but only on bank 1 (I have a V8). Graphing sensor voltages showed that bank 1 was skewed towards being lean. I replaced the sensor (just the one) and the lean code went away (rather, I cleared the code after the repair, and the code did not return). Interestingly, the PCM then "realized" how slow the bank 2 sensor was compared to a new one and triggered a "bank 2 oxygen sensor slow response code". Graphing the voltages of both sensors shows, in fact, that the frequency of bank1 is faster than bank 2.

If you decide to do anything with injectors, they can be cleaned on your bench rather than replaced. This can be done using a spray can of carburetor cleaner (Berryman's B-12 Chemtool works well), some rubber hose, a 9V battery & some wire leads. Connect can of carb clean to the injector with rubber hose (will need to get creative here), then connect battery to leads on injector (do this momentarily, the PCM never applies voltage to an injector for any length of time so neither should you. Pulse the voltage) to open the injector. I pressurize the rubber hose with carb clean, then electrically switch the injector open. Watch the spray pattern, usually it starts as a poor spray with large drops (dirty injector) and after a few cycles of this it's a very fine mist with four distinct holes (at least on my orange body 19lb/hr injectors of my 96' F150). Confused? Check YouTube for ideas/more info (search "DIY injector cleaning" or something).