Hello. I have a 1996 f150 4.9l with 205,000 moles on it my dad had the truck before me and the check engine light has been on for as long as I can remember. I scanned for Dtc's and got p0171 and P0174 I found out this means it is running lean, I have researched it an there are allot of things it could be I've
o changed both fuel pumps and the fuel filter
o did seafoam last week
I am 18 and do not have allot of money so what are the usual causes of this?
The more I read I am thinking it is the o2 sensors I just want to make Shure before I buy them

Also, my dad and I were going to bump the timing but saw under the hood that the timing is not adjustable. Is this true or did ford just say that so people did not mess with it?

Scott

 

Could be O2 sensors but usually when it throws lean codes for both banks you need to look at the mass airflow sensor sometimes you can clean them and get them back going.
Also if the valve seals are leaking oil by them you’ll get both codes , or a vacuum leak behind the m.a.s. or if you have a K&N or other oil type filter and have too much oil on them or a dirty pleated type air filter will cause both codes.

 

I agree, but if you've got over 60k on the o2's, that's a good enough excuse to replace the ones (o2's) ahead of the Cat.

Do you have one of those imfamous "cold air intakes"?

On Advancing timing, the last thing you want to do if running lean. Also, not the easy task it is w/ OBD1's. OBD2's, further advance is done by modding ECU.

 

What do you mean by cold air intake?
Also where is the best place to buy the o2 sensor? Do I have to get it from ford or will the parts store be fine?
I was just curious about the timing I do not think I will advance it now.

 

Look for air leaks after the maf sensor, that could cause the codes.

 

Something like this (I'm in no way suggesting you get one):



Just shop around for the best price on "Bosch" o2's for your year & engine.

I believe that's who makes em for Ford anyway.

Those are usually the Code numbers that are displayed when they go, but as Nitehawk pointed out, both banks seldom if ever go at the same time. So more likely something going on upstream of both.

Anyway, anytime you replace, do them at the same time. Don't leave an old, slower switching, less accurate one on one bank & anew on on the other.

I'm an OBD1 guy. I'm assuming your OBD2 set up is one on each exhaust bank.

 

I made a copy of a k&n cold air intake that was on a friends truck I just put it on 500 miles ago, it had the code before I put it on. The truck had a drop in k&n before that. Are you thinking the maf is dirty? If so how would I clean it?

 

Just had the same problem on my 04 f150, turned to be a vacuum leak. With the truck running spray some carb cleaner on the vacuum hoses when you notice a change in idle then start looking there. Mine was just a vacuum hose that came off good luck boss

 

Could also be the mass air flow (MAF). To clean just get some MAF cleaner and spray on it.

 

Disconnect it, remove it, spray elements w/ MAF or Electronic Contact Cleaner, don't touch elements w/ finger, replace.