I had the light come on a few days ago and had Autozone run the code. It was a 171 and a 174, which is bank 1 and 2 running lean. I've checked all the vacuum hoses and other areas, but see no problems. I changed my fuel filter about a month ago, could a bad fuel filter cause this? It seems to run good except after driving it awhile I will occasionally get a rough idle, which will usually smooth out after reving it. The vehicle has 84,000 miles on it and I hesitate to change the Oxy sensors if it's not needed. It just seems strange that both sides would go out at the same time. Any suggestions?

I've seen a few others on here that have had the same codes, what have there solutions been? The Navi will probably going into the shop later this week if I can't figure it out.


PS- I have disconnected the battery to clear the code, but it came back after a day of driving.

 

I am going thru the same thing. I can tell you now, it is the Idle Air Control sensor. It is a total pain the behind to get to. I pulled it and cleaned it and it worked for a little while. It is doing it again. I called the local ford place for a new one and it is about $65.00. I also changed the throttle position sensor on the recommendation of the computer at autozone, but it didnt change a thing. In fact now the transmission shifts a little weird.

The sensor you are looking for is on the back of the throttle body near the fire wall.(I have a 5.4L and that is where mine is.) If you need photos of where it is and how terrible it is to get to let me know. I can take some while I change mine tonight.

I do have a question, when I put the TPS on it didnt seem to want to line up correctly. I was spring loaded and went on at an angle. I moved the throttle so the spline would line up with the sensor. Was the correct way to install that??

 

You're running lean, so the O2 sensors are detecting too much air and not enough fuel. It's either a fuel flow problem or a sensor problem if there are no vacuum leaks.

If you've checked and ruled out a vacuum leak, you may want to clean the MAF sensor. If the sensor is dirty, it may not be measuring all of the air that passes. The computer wouldn't read this until after the combustion process so the next sensor in line is the O2, which is telling you that you're running lean.

If cleaning the MAF doesn't fix this, it would lead me towards fuel flow problem. It would be very peculiar to have both upstream O2 sensors fail at the same time.

 

I came across this check list:

: P0171 - P0174 System to Lean : The Adaptive Fuel For lean and rich

Fuel system:
-Excessive fuel
-Contaminated fuel
-Leaking fuel
pressure regulator.
-Low fuel pressure or running out of fuel.
-Vapor recovery system.

Induction system:
-Air leaks after the MAF.
-Vacuum Leaks.

PCV system:
-Improperly seated
engine oil dipstick.

EGR system:
-Leaking gasket.
-Stuck EGR valve.
-Leaking diaphragm
or EVR.

Base Engine:
-Oil overfill.
-Cam timing.

Cylinder:
-Compression.

-Exhaust leaks
before or near
the HO2Ss.

 

Thanks Aj and Robby. I appreciate yout input. I've checked about all that I could and will probably be sending it into the shop to have it fixed.

 

Add to that list: Dirty injectors which I guess could be classified as contaiminated fuel.

What happens is a piece of dirt gets in the injector ('s) and flow is interupted. The only way the engine can pick this up is the O2's and it sees that there is lots of oxygen in the exhuast.

Lots of things could cause a lean condition. Hope you figure it out. If I find any info I'll let you know.

 

90% of the time its a vacuum leak throwing those codes. I found (on my 5.4)at the back of the engine, with the help of a master Ford tech a rubber boot that splits. He said it is extremely common. Follow your pcv valve tube all the way to the verry back of the engine. Pull the boot and check it. Mine had a split at the crease that wasnt visible till I pulled it.

 

Thanks Throttle. I'll check that out.

 

Throttle,

Checked the rubber boot at the end of the PCV hose. I couldn't get it off, but when I put my finger on the back of it with the engine running, it definitely would suck my finger in. Looks like a leak to me. Hopefully this cures my problem. Can you get just the rubber boot, or do you have to order the whole PCV hose? I'll get it changed tomorrow and disconnect my battery to clear the code and hope for the best. Thanks again for your help.

 

I had to purchase the entire kit for around 20-25 bucks. It's a cheap fix, but there wasnt anything I found to sub for the original. I didnt want to take the chance. The 97-02 f-150 and navigator all use the right angle boot. The hard tubes are different but you can always reuse the ones you have.

 

Yipee! It worked! So far no check engine light has returned and it runs as smooth as ever. Thanks everyone for your help, especially you throttle.

My cost on the PCV hose was $16.11 and about 15 minutes of labor. I bet this would have been at least a $150.00 job from the shop. Heck they wanted $66.00 just to hook it to their computer. Now, what can I buy with the money I saved.

 

Super Advice!!
I have to say thank to everyone who posted information on OBD II codes P0171 and P0174. But the one thing fixed my check engine light problem was the rubber elbow (Ford should redesigned this part) at the end of the PCV tube; locatede behind the Throttle body. So, the $70 dollars engine check the dealership wanted turned out to be a just few burnt eyelashes( reading thru the different webpages I went through) and more money in my pocket since I only spent less than $5 on the folowing part. From Help CompanyPCV System Elbop Part # 47028. The only modification I had to do to the part was to wrap electrical tape around the PVC tube end that goes behind the throttle boddy because is just a little bit thinner than the elbow. If you do not do this it will suck air through it and you may not be able to clear the code. Good luck!

 

topito

Where exactly is this boot? You say behind the throttle body? I'd just like to know so I can check if I ever get that code...

 

Best way to find it is to start at your PCV valve in the left valve cover. Follow the tube back behind the engine and you will see (or most likely feel) where it attaches into the manifold. Seems to be a very common problem and I would suggest that you change it at 75,000 miles if it hasn't been replaced before. I wasn't able to find just the elbow at the dealer, so I purchased the complete PCV valve hose for $16.11. It also came with a new PCV valve. It's a fairly simple job.