Getting codes 171 and 174. How to fix? So far, havn't found any vacuum leaks.

 

It's either and air leak into the intake after the MAF, the MAF sensor, or low fuel pressure -- something like that. I'd look for vacuum leaks first. Have you done any work on the vehicle lately?

Also, clean your MAF. Always a good idea when emissions related codes pop up.

 

DTC P0171 and P0174 are set only during closed loop feedback operation when the PCM is monitoring the oxygen sensors. WOT is never closed loop.

The 171 and 174 codes mean that the Long Term Fuel trim has been enriched to the calibrated limit at one or more cells in the correction table. Basically, the PCM is saying that there must be something wrong to require this much enrichment correction.

When both banks are lean, the first thing to look for is an unmetered air leak before the throttle body, then look for a vacuum leak after the throttle body. A notorious leaker is the PCV system and it can contribute to either depending on where the leak is.

If that's OK, you could have a dirty MAF, clogged fuel filter or low fuel pressure for some other reason. Lower manifold gaskets, clogged injectors or bad O2 sensors are also possibilities but often affect one bank before the other.

EDIT- John beat me to it! Again! While I was composing, he was posting.

 

Now wait just a minute here! I may have beat you, but by golly yours was higher quality, lol!

 

I thought that they looked remarkably similar.

 

I guess I had already fixed the problem and didn't realize the computer had to be reset before the check engine light would go away. I had previously found the pcv line disconnected allowing unmetered air to the manifold. After resetting the computer to remove the codes from memory, I've driven over 150 miles today and the light did not come back on.
Thanks to John and Bob

 

I'm getting the same two codes (P0171 & P0174).

The local consensus is I should replace my O2 sensors. Does anyone know the values to check them or other ways to test them?

...and i just realized this is now in the wrong forum. I have a 3.0L.

 

i have a similar problem.

 

On fords the main problem they have is with the hose on the PCV, it turns to junk quick normally. Now if you have a 3.8 and have a 171/174 its the valve cover doing it. If its a 4.0 its usually the PCV hose / dirty MAF.

 

Is the same PCV/hose problem common on 3.0s?

 

I have several times dislodged mine where it joins the valve cover -- not the smartest thing in the world. Especially since I wheeled and got muddy water in that hole -- DOH!

No lasting damage, but my oil test from that batch had high silicon levels -- no surprise there, lol.

I don't know if it's common, but I haven't replaced my PCV yet. Some kind of air leak is the usual culprit though in those lean codes.

But a bad MAF can be a culprit, as we discussed at the beginning of this. If the MAF simply reports less air than is flowing through it, that's the same problem.

Ryan, it's unlikely to be that BOTH your oxygen sensors are bad. It's much more likely a bad MAF or air leak.

 

Thanks again.

I thought mud in the engine just added character...?

 

Or an intake gasket leak.

I've been hearing more and more about SOHC intake gaskets causing lean codes. Not unlike the OHV in that regard. Just something to consider.

 

Hi Ryan, it's been a while!

I agree with the other comments that say to check things that affect both cylinder banks first - vacuum leaks, unmetered air leaks, dirty MAF, etc.

Checking the oxygen sensors is a bit tricky because the voltage values should be constantly changing when the fuel delivery system is in closed loop control. Try this link for some ideas on in-vehicle and bench testing of the O2's.

Your oxygen sensors have 4 wires each. The color codes for the signal wires are gray/light blue (PS) and red/black (DS). For 97, the signal return common to both sensors is solid orange.

 

Uhh...mud in the engine COMPARTMENT adds character, lol. Mud in the engine itself is of no personal benefit...

 

Thanks for the reading Bob. I like that kind of useful stuff.

Since I'll be starting with the MAF, is there any problems cleaning it in place? Or will the cleaner cause problems?

 

Usually doesn't. Worth the attempt.

 

I've also gotten these codes when the IAC was bad...

 

i've got the same codes right now (my CEL is on).

someone mentioned to me on AIM where to look for the PCV valve, but i forget where they said to look. anyone know where i could find it to check it out???

 

I know this thread is old, but I just had the codes 171 and 174. I found a nice size rip in a 90 degree rubber tube leading to the PCV valve, which is just near the throttle body. I got a $5.99 piece of similar angle rubber tube from Advance Auto and installed it the same as stock, reset the ecu and no more light. Simple fix.

 

well i hab been getting these codes for almost a year and couldnt track it down i changed the maf iac and did the intake gaskets and after all that it was a bad iac.
if you have a low and/or erratic idle its most likely the iac

 

did you reset the computer