Smrtass498

Hello -

Not sure where everyone is located but I am in Northern CA, and the lowest octane avaliable in CA, is 87...so I have never ran anything less in the truck. I did replace the PCV valve when I did a tune up a while back when the light was still on, and replacing it did not get it to go off. I suppose I could double check to make sure it's still good.

I have not checked for basic intake leaks...guess that's my next step.

The problem with my fuel return switch is that my fuel is not returning into the same tank it came from. Example: If one tank is empty and the other is full...by the time the gauge gets to half a tank, I can switch tanks and the empty one will now gauge at maybe a quarter of a tank or whatever was not returned to the full tank. My mechanic said he just did this on another Ford and it is quite an expensive part. I may hold off since it really doesn't have anything to do with the performance of the truck itself.

Truck still runs like a champ (haul a horse and trailer), just want to get that irritating light off....and I'm positive there is something not right, but nothing major, so I do want to fix it and don't want to just unplug the light.


Jamie

SteveinWA

I've been reviewing all the treads because I too have a 1996 F150 with PO171 and PO174 causing the "check engine" to come on. I did manage to pass the truck through emissions because occasionally the light will stay off for days allowing the computer to gather good clean data. Other times the light returns immediately after resetting it.

couple things: I bought truck just recently and I knew there was an "engine light" issue. First, he did mention to me that if the front gas tank is empty and he is running of his back tank that gas flows back to the first tank and evens things out. Does anyone know if this is Fords design????
I read in one of the threads that someone suggested a bad fuel pump in the front tank which might cause "lean" while using that tank. --Made me think... I did pass emissions because the light stayed of the longest on the back tank! Once I filled up both tanks and switched to the front tank my light came back on... Was that coincidence??? Just a thought. I'd like to hear what you all have to say about that theroy.

Second... just so we can keep a run down... An O2 sensor was replaced just before I bought it... I'm unclear if it was 1 or all. I replaced the MAF sensor, replaced several vaccuum hoses, fuel filter... had it to Authorized Ford repair shop, still the light is on. I'm replacing the engine coolant temp sensor (the sensor the computer uses) today. i'll let you know.

Last.. I see the tread kinda ends as of May 2008... did everybody give up or did you find the golden egg?

Thanks, Steve in Renton Washington

Good old Bill

Welcome to the site Steve, have you used the search button for additional info.? I believed I corrected my PO171 and PO174 codes by replaceing the intake seals on the plenum chamber that is used on the 4.2L V-6 engine in my 2002. Suggest try talking to the back counter parts people at the dealerships, these are the wholesale people who also tend to their mechanics. Am getting off track here as to your engine, in the search button they talk of the intake runners as being the cause. Check it out.

SteveinWA

oh...one last question... where in the "HECK" is the PCV valve on a inline 6??

SteveinWA

Thanks Bill! Ya... this looks like a good site. Do you happen to belong to a good FORD in general forum you might recommend? I have 3 of them. I did use the search button and thats how I came across this particular thread. Seemed that it most matched my struggle and the fact that these 2 guys were also questioning their "tanks" at one point made me wonder if the tanks were working as designed or if it really was a common problem that all 3 of us had!??

I appreciate your suggestion about the gasket. According to paperwork in the glovebox this gasket was replaced along with an O2 sensor right before the guy decided to put it up for sale and bought a new truck.

Thanks again!
Steve in Renton Washington

Just call me Sean

iTrader: (1)

The PCV valve is on top of the valve cover, inserted in the rubber hole. The fuel pumps have a valve in them to prevent fuel from being transferred to the wrong tank. If the valve is faulty, the pump must be replaced. If the rear tank is on and fuel is being pumped to the front tank then the front pump valve is bad. This being said, why do these codes have the CO in front of them? Is this just how they are written or is there a different code list for the newer OBD system? My code list says:
171- Fuel system at adaptive limit, HEGO unable to switch
174- HEGO switching time is slow

SteveinWA

Thank you.

Well unless I'm blind the PCV valve must be buried under the intake manifold. I guess that's kind of a statement/question!?

Interesting about the gas tank. I'm going to watch myself now and see if I experience that issue.

For the codes. These are the OBDII codes. PO171 and PO174

Thanks for your help!!

Just call me Sean

iTrader: (1)

Ok, I see. Apparently my book is for OBDI only. The book goes to '96, so I assumed they were the same. It makes sense though, since you need a scanner for '96 and up and the scanner usually tells you the code definition anyway, so you wouldn't need a list of definitions.

And this is the PCV valve:

SteveinWA

Thanks for the pic! That's were I expect to see the PCV valve as well but Noooooo! Actually my inline doesn't look anything like your picture. I have a big intake manifold laying on top of mine... say over the back 2/3rds of the cam cover. Guess I could take a pic in the AM if that would help.

Again, thank you for your help!!
Steve

Just call me Sean

iTrader: (1)

The book says if it's not on the valve cover or oil cap, it's on the rear of the intake manifold. It will have a fuel line sized hose on it, like the size of the one in my picture.