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dreaded P0171 and p0174

N

NIghthawk1824

CEG'er
Joined
Jul 27, 2008
Messages
226
Location
st.Louis ,MO
98.5 Contour SVT

So I threw the codes P0171 AND P0174 (system bank 1 and 2 lean) about 5 months ago, they came on with out me installing anything or putting anything new on, So far i have replaced UIM and LIM gaskets, swapped maf sensor (cleaned also) and reset codes, came back on about 3 days later, Cleaned IAC (8 months old) and checked PCV all good, I installed headers about 2 months ago and still have codes, (running MIL's) I have also sprayed just about everywhere i can think of with starter fluid to see if i would be able to get a change in idle,
* i do have a small exhaust leak from the front header but its on the far right side away from the o2 sensor, So i do not think this could cause the code since i had it before headers. (no leak before i installed headers)

Any thoughts are welcome, I have searched a lot of other people with the same problem and it seems to be either a vacuum leak or a MAF sensor but i can not find one, Could i somehow just have a bad o2?
 
*update Pulled lower and upper intakes again and bought new gaskets for TB, UIM/LIM, EGR, and checked all vaccum hoses... I also did a fuel pressure test and came out just fine.. I looked at my short term fuel trims and i am up around 20+% on both bank 1 and bank 2 My 02 seem to be changing volts constantly and my MAF us at 2.50 g, Anyone have any ideas?

when driving my long term fuel trim will drop to the normal range but the second i am off throttle its back to 24.98% and never moves
 
Rarely do these codes have anything to do with the O2 sensors. Since you have done and redone the gaskets I would look elsewhere. Because you have both codes indicates that the problem is not localized. Did you change the fuel pressure regulator while doing the gaskets? Check for other fuel restrictions such as clogged / old filter, crimped supply line, malfunctioning fuel pump. The following is a trouble shooting list for the codes. Usually start at the top and work your way through.
P0171 - System Too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The code is set when the adaptive fuel tables reach a rich calibrated limit.
Fuel System:
· Contaminated fuel injectors
· Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
· Vapor recovery system (VMV)
Induction System:
· MAF contamination
· Air leaks between the MAF and throttle body
· Vacuum leaks
· PCV system concern
· Improperly seated engine oil dipstick
EGR System:
· Leaking gasket
· Stuck EGR valve
· Leaking diaphragm or EVR
Base Engine:
· Exhaust leaks before or near the HO2S
· Secondary air concern
Powertrain Control System:
· PCM concern

P0174 - System Too Lean (Bank 2) Same as DTC P0171, but Bank 2. See Possible Causes for DTC P0171
I believe if you work your way through this list you will have your answer.
 
i checked fuel pressure and at idle i am 43 psi and when i give it throttle it jumps to about 60, I changed o rings on the fuel injectors and they looked clean,
 
With the other things that you have done the next thing on the list would be the EGR valve. Remove the vacuum line, apply vacuum with either a pump or you can suck on line. If the vacuum stays steady and the engine runs poorly and stalls then the valve is working correctly. If the vacuum does not remain steady and the engine runs fine the valve is most likely bad. If the vacuum is steady and the engine runs fine remove the EGR valve and check the tubes for carbon blocking passages. If the valve is fine go to the next item on the trouble shooting list.
 
I'd have done my O2 sensors before all of that. In fact, I cured a P0171 with a new O2 sensor on my 95 a few years ago.
 
The fact that the fuel trims are messed up at idle but ok with throttle almost 100% means you have a vacuum leak. Think about it, a pinhole in a vacuum hose is significant compared the the normal idle air flow, but when driving that pinhole is nothing compared the the amount of air entering the engine.
 
Yea my trims go back to normal when driving, I just cant think of anywhere else to look for a leak, I guess i will have to have a smoke machine used, I doubt i would be able to see the leak since i have already gone over all the hoses i can think of,
 
I went through all this a couple of years ago. Only thing that fixed it was the intake manifold gaskets, but that was after I'd did all the other stuff. I definitely found the gasket leak with the use of carb cleaner spray. I changed O2 sensors along the way too, which is about the only thing you haven't done yet. 3 are easy, one in back is a PITA. Really all you would have to do is the upper ones, but that includes the PITA one. The lower O2 sensors just check the cat performance. I replaced rather than cleaned my IAC (some controversy surrounding the 'cleanability' of that part), and it being fairly cheap made the decision easy. Might the IAC not working right mess up your idle trim rather than a vacuum leak?
 
I changed IAC valves about 10 months ago, I did try cleaning it to no change, I do not have lower 02's (mil's) my uppers i have not changed yet...I had an exhaust leak (headers) so i fixed that today and i am just awaiting results, the leak was quite small though.
 
Here is my end-all, top-secret fix for the check engine light. As long as the engine is still running, use this trick. Take a small piece of electrical tape, trim it carefully to shape, and stick it over the check engine light. Make it black electrical tape to match the background.
 
NIghthawk1824 said:
I changed IAC valves about 10 months ago, I did try cleaning it to no change, I do not have lower 02's (mil's) my uppers i have not changed yet...I had an exhaust leak (headers) so i fixed that today and i am just awaiting results, the leak was quite small though.
Click to expand...

The list of items to look for codes p0171 & p0174 are from the Trouble shooting bulletin from Ford. This is directed to professional mechanics. None of the items that you did with the exception of fixing leak is even on the list. Normally I would not even question the reason for changing O2 sensors. They are regular maintance items. But they are not listed on the tsb. If you want to be successful follow the plan laid out by the maker of your car. If you just want to buy random parts with little chance of success, I guess the auto parts industry needs help out of the recession.
 
Spikedog said:
Here is my end-all, top-secret fix for the check engine light. As long as the engine is still running, use this trick. Take a small piece of electrical tape, trim it carefully to shape, and stick it over the check engine light. Make it black electrical tape to match the background.
Click to expand...

Sounds great, except for the states that require emissions testing.
 
Spikedog said:
Here is my end-all, top-secret fix for the check engine light. As long as the engine is still running, use this trick. Take a small piece of electrical tape, trim it carefully to shape, and stick it over the check engine light. Make it black electrical tape to match the background.
Click to expand...

that is the most stupid and dumb suggestion ever. if the CEL is on, its on for a reason! it shouldn't just be ignored :nonono:
 
Spikedog said:
Lighten up, BrApple. Do you not recognize a wee bit of levity? Start with the first sentence.
Click to expand...

ok, missed that ... was to early in the morning I think .... I just take the troubleshooting forum seriously as someone is going to read that out of context and think its a real solution.
 
Dan the rug man said:
The list of items to look for codes p0171 & p0174 are from the Trouble shooting bulletin from Ford. This is directed to professional mechanics. None of the items that you did with the exception of fixing leak is even on the list. Normally I would not even question the reason for changing O2 sensors. They are regular maintance items. But they are not listed on the tsb. If you want to be successful follow the plan laid out by the maker of your car. If you just want to buy random parts with little chance of success, I guess the auto parts industry needs help out of the recession.
Click to expand...

not really sure what you are trying to say? I did half that list so far and still have a problem...I have looked through a lot of the older threads and have followed what others have done to fix there codes, No luck for me so i started my own thread to get some input, My 02's are fine, I had to dyno tune my other car (383 stroker) and i asked the tuner if i could have him watch my 02's...he said they are in spec.

I am due for safety and emissions here at the end of may so i am trying to get it fixed now,
 
BrApple said:
ok, missed that ... was to early in the morning I think .... I just take the troubleshooting forum seriously as someone is going to read that out of context and think its a real solution.
Click to expand...

Well, I hope nobody takes it out of context.

And on the other hand, the CEL is pretty distracting during night driving, and not being able to keep it off is pretty (VERY) frustrating. You can still see the glow of the yellow CEL without it affecting your night vision under that tape (wonder how I know this?).
 
the light is annoying i agree but that's not what i am worried about, I would rather make the light go away because i fix the car not because i fix the gauge. But i do understand it being annoying especially at night
 
NIghthawk1824 said:
not really sure what you are trying to say? I did half that list so far and still have a problem...I have looked through a lot of the older threads and have followed what others have done to fix there codes, No luck for me so i started my own thread to get some input, My 02's are fine, I had to dyno tune my other car (383 stroker) and i asked the tuner if i could have him watch my 02's...he said they are in spec.
,
Click to expand...

What I am trying to say is that the next step in the trouble shooting chart is to look at and test the EGR. Look back at the previous post on how to check that. I am not saying that this is the answer but that it is the next step in the process.
 
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