Need help
I'm getting trouble codes P171 and 174 which is lean burn bank 1 and 2.
Also codes P1131 and 1151 which is bad o2 sensors.
Would bad o2 sensors cause me to get the lean burn codes also?

I've already checked for vacume leaks and checked the PCV lines and can't
find anything.

 

P1131 and P1151 don't necessarily mean bad O2 sensors. Those codes are saying that the upstream O2s are stuck lean and short term fuel trim isn't able to make them switch lean-rich-lean-rich. O2 sensors are tattle tells, the only time they really go bad is when the heater circuit fails in them (there's specific codes for that, um, P0135, P0145 I think) or when they get contaminated from things like an internal engine coolant leak.

When there's codes saying that both banks are lean, we need to start looking for things that'll affect both banks. Faulty mass air sensor, uncommanded EGR flow, vacuum leaks after the MAF, and so on. I know on some later model 4.2 liters, there's a TSB for replacing the bolts and gaskets between the upper and lower intake manifolds, since outside air can seep through them and cause P1131/51. I know you've checked your PCV tubes and whatnot, but look real hard for any vacuum leaks. Look at the mass air sensor, make sure there isn't any brown fuzzies or anything like that on the heated wire.

 

Quintin,

Really can't agree with this assessment.

O2 sensors get lazy as they age. This leads to slow, ragged, or delayed switching. They are very obvious when the output waveform is viewed on a scope.

My opinion is that the truck in question has both worn out O2 sensors AND at least one of the other issues you raised.

The 1131 and 1151 codes relate only to the switching rates of the sensors. The 0171 and 0174 codes indicate a maxed out fuel trim. He has both.

Steve

 

i am having the same codes right now, fuel bank 2 too lean, changed all 4 O2 sensors and still the same code, just changed out all the gaskets under the plentum and now there is a real bad vacuum leak after I put it all together, I know the gaskets were done right, are there any vacuum hoses that hook to the rear of the plentum that i did not see? i can hear the air when i tap the gas but i cant figure out where its coming from

 

Steve, I agree, although I think it'd be advisable to address 0171/0174 before condemning any O2 sensors.

 

Quintin,

Sure, but I'd buy the sensors and have them on hand anyway....


fnf150,

Based on the limited amount of information you gave, you definiately wasted your money on at least two of the sensors (downstream). Probably on the two upstream ones as well since "lean" codes usually aren't sensor problems. Sorry... Post your exact codes for specific help or just SEARCH using the code or codes as your search keywords.


Since you can hear the leak, use your shop air dialed down to about 5 psi and pressurize a vacuum line (engine off) such as a brake booster line. It will be easier to hear the air escaping.

Steve

 

Guys,

I'm nothing more than a rank amateur, but I can tell you that I recently had troubles with my o2 sensors as well. I had an P1151 reading (lean) and replaced the affected o2 sensor and the problem is gone.

The Mechanic did mention that time plays a heavy role in their condition, and that the downstream sensors are not quite the same as the upstreams.

Mine is a 97 F-150 F/I V-6 4.2l 2 WD.

Thanks,

 

it very well could be his MAF sensor and it just needs a cleaning and that might make the problem go away...