codes again

2000 f-150....4.2 V6....112,000 miles.

I changed the egr valve..checked and cleaned hoses(vacumn passages) and port...did not remove intake manifold (Too Cold)...clean Maf sensor...new gas/air filter.

The truck ran ok for a few days BUT now stumbles, hesitates, misses and sometimes backfires. Sometimes it runs just fine..go figure. I have A po402 code again AND a po171 code. The people at advance auto say I need a oxygen sensor for the po171 code(bank1..too lean). Before I go on a search and destroy mission and change every sensor (pricy) , I wonder if anyone has a suggestion?

Thanks again!

2000 f-150....4.2 V6....112,000 miles.

I changed the egr valve..checked and cleaned hoses(vacumn passages) and port...did not remove intake manifold (Too Cold)...clean Maf sensor...new gas/air filter.

The truck ran ok for a few days BUT now stumbles, hesitates, misses and sometimes backfires. Sometimes it runs just fine..go figure. I have A po402 code again AND a po171 code. The people at advance auto say I need a oxygen sensor for the po171 code(bank1..too lean). Before I go on a search and destroy mission and change every sensor (pricy) , I wonder if anyone has a suggestion?

Thanks again!
Don't remember what#402 is off the top of my head, but 112k is overdue for o2 sensors. o2's ahead of the Cat relate to fuel trim. after the cat is basically to let you know when the Cat is pooched. When 2 are before the Cat (Left/right manifolds for most V8's), they should be replaced at the same time.

P0402 is excessive egr flow. Possibly the DPFE sensor. The O2 sensor usually will not set the P0171 code. Look for a vacuum leak that only affects one bank.

Was there a gasket on the EGR valve?
If replacing any HO2 sensors, save 50% by just doing the upstream sensors.
The upstream HO2 sensors are used for the Air/fuel mix.

the egr valve has a gasket....I once changed a o2 senser (3 years ago) passenger side, before the cat. Is that what you mean when you say "upstream". Should I change the other one (drivers side)

I seen on other posts that the DPFE sometimes also goes bad with the egr...would that cause excessive air flow.
Holy Cow, what a mess. Thanks!

Passenger side = bank 1 (cylinders 1-4)
Drivers side = bank 2 (cylinders 5-8)

Yes! The upstream HO2 sensor is befor the catalytic converter.

It sounds like the one on bank 1 is bad again!
Most HO2 sensors from an auto parts store have a 1year warranty.
Try rolling the upstream HO2 sensor from bank 1 to bank 2, and clear code.

Befor replacing DPFE sensor, check the PCV system for unmetered air leaks.
Because of age + mileage, suspect bad plastic, rubber, seals, and gaskets causing unmetered air leaks.

Thanks for the great advice. I will swap 02 sensors and see what happens!

This engine is a v-6...are cylinders 1..2..3. (bank 1) still on the passenger side?

Yep!

For the P0171 code, have you replaced the intake isolator bolts and intake plenum gasket??? Most likely that is where the code is coming from if it is not coming from oxygen sensors.

check out the fix here
http://sites.google.com/site/fordf150p0171p0174fix/Home/

This fix by yourself should take less then a day to fix as long as you have everything you need.

If the problem stays the same, do a smoke test for vaccum leaks, see
www.youtube.com/watch?v=FfiQ7qWiG-M (http://www.youtube.com/watch?v=FfiQ7qWiG-M)

Suspect the EGR gasket, DPFE sensor, or intake gasket.

Thanks again guys..looks like I have my work cut out for me.
Gorden-gjs...great article with pictures...a summer project for sure if needed!
Danielsatur...a smoke test is in order...maybe I'll get lucky
Way2old...thanks for the info, a smoke test should help!
Dfordski...02 sensors ordered

Thanks one and all....will let you know what I find!