p0171 p0174

[asalford]

having some trouble with a 2001 taurus 3.0 duratech DOHC. CEL came on while my wife was driving on a long trip. When she brought it back and I began checking it out, I immediately noticed stumbling during idle. Car otherwise seemed fine during driving and acceleration. I cleared the codes and they came back the next day.

Scantool shows the following:

error codes p0171 & p0174

STT bank 1 & 2 seems locked after a short while @ 9.0
LTT shows no data after a while.
Both STT & LTT seem to work properly when the car is riding down the road and on previous code scans before the p0171 showed up.

When reading fuel system says the loop is closed, but fault with one or more O2 sensors

O2 sensor data seems to be ok when compared to previous scans.
MAF show from 0.3-6.0 lb/min.

Findings:

on the valve cover, there is a plastic tube with 90 degree rubber piece that connects to the intake behind the MAF. the rubber piece seems to have disintegrated and makes a half way seal. <<=== this has been this way for some time. Can this be the source of the problem?

I have removed and cleaned the MAF and the codes returned. There was some oily residue around, on, and in the sensor.

if i hit the accelerator, the Fuel Trim seems to unlock and begin working normally. After a while at idle after this, it will begin rough idling and the fuel trim will again lock in @ 9.0 on the STT.

I checked for a vacuum leak with some carb cleaner around the intake manifold, maf sensor, and the disintegrated rubber hose looking for the Trim to go crazy. It did not.

[shorod]

Welcome to the forum!

These two codes in particular have been addressed numerous times. Please try the "Search this forum" link from the Taurus forum main page to perform a keyword search. I think you'll find a lot of information on this topic.

-Rod

[asalford]

I thank you in advance for reading this post and appreciate your feedback.

I agree, I have read a wealth of data on the subject from this site in particular and from browsing around the web. I thank all of those who took the time to write those posts. I am hesitant to replace the MAF sensor @ $160 without a higher degree of certainty this will resolve the problem. I am getting readings from the sensor which seems to indicate it is working. more accelerator, the higher the readings and the typical readings that are present on this site from other scantool output.

I felt my situation was different because the scantool was indicating a "fault with one or more O2 sensors", but when i look back on previous/normal scans, the O2 output readings seem similar. I have also read the O2 sensors are rarely the case and 90% of the time cleaning the maf clears the problem. I have done this. I also plugged the hole on the valve cover to intake tube and have the same condition. I have also hit around the intake with carb cleaner to see if serious trim fluctuations occur. They have not.

I have not read or found where the trim settings b1 & b2 would lock @ 9.0 and this is when the stumbling at idle began occuring. Another thing that I noticed is that it locked after idling for approximately 60s or more. if you tap the accelerator the trim functioning would return to normal looking operation and will lock again after about 60s of idling

[shorod]

The fuel trims locking at 9 is probably not the issue, but rather the result of the stumbling at idle.

According to the factory service manual, likely causes for these codes are as follows:

• Fuel system
• Excessive fuel pressure.
• Leaking/contaminated fuel injectors.
• Leaking fuel pressure regulator.
• Low fuel pressure or running out of fuel.
• Vapor recovery system.
• Induction system:
  • Air leaks after the MAF.
  • Vacuum Leaks.
  • PCV system.
  • Improperly seated engine oil dipstick.
• EGR system:
  • Leaking gasket.
  • Stuck EGR valve.
  • Leaking diaphragm or EVR.
• Base Engine:
  • Oil overfill.
  • Cam timing.
  • Cylinder compression.
  • Exhaust leaks before or near the HO2Ss.

Have you checked the operation of the EGR system, the readings for the DPFE, and the fuel pressure?

-Rod

[asalford]

I recently dealt with a defective back pressure sensor and don't remember the exact code but was a general EGR system problem. It crumbled in my hand when I touched it. Although I checked the egr valve & switch recently during the diagnostics (maybe 4 months ago), I have not checked that since these codes came up. I will be sure to do that.

I will check for vacuum leaks. I was not aware the duratec DHOC had a pcv valve. The manual i have only shows a standard 3.0 engine where it sits on top of the valve cover. do you know where it is located on the engine?

cycliner compression is @ 85-90 psi
fuel pressure is 55 psi.

Wife also reported horrible performance this morning. only thing i did yesterday was plug the hole with the valve cover tube to the intake yesterday.

I'll get to work on this list and get back with you. Thanks for the post

[shorod]

On the Duratech, the PCV valve is located at the intake manifold below the throttle body. It's not real fun to get to.

-Rod

[asalford]

Rod thanks for the help:

According to the factory service manual, likely causes for these codes are as follows:

• Fuel system -- 55psi constant
• Excessive fuel pressure.
• Leaking/contaminated fuel injectors.
• Leaking fuel pressure regulator.
• Low fuel pressure or running out of fuel.
• Vapor recovery system.
• Induction system:
  • Air leaks after the MAF.
  • Vacuum Leaks -- warm holds steady 20 psi of vac
  • PCV system. <=== discovered the hose/elbow was collapsed
  • Improperly seated engine oil dipstick. -- seated properly
• EGR system:
  • Leaking gasket.
  • Stuck EGR valve. -- operates with a hand vac properly
  • Leaking diaphragm or EVR.
• Base Engine:
  • Oil overfill. -- OK
  • Cam timing.
  • Cylinder compression. 85-90 PSI
  • Exhaust leaks before or near the HO2Ss.

Have you checked the operation of the EGR system, the readings for the DPFE, and the fuel pressure?

I found the rubber elbow on the pcv oil seperator tube collapsed whiling the engine is running & has a crack in it. once i get a replacement, dealer only item, i'll let you know the milage i get from this repair. plugging the tube stops the p0171 & p1074 & multiple HO2S fault.

Again, thanks for the help.

[carlos80]

P0171 and p0174 are almost always telling you there is a vacuum leak. You can check for this, if a scan tool is available, by looking at what the IAC valve is doing. It will usually have a lower reading than normal(trying to close to compensate for the vac leak).

[shorod]

Sounds promising. Good luck!

-Rod

[Huney1]

Get some of the real stuff - CRC MAFS Cleaner - available at most parts stores and clean it again. Spray it on let it dry and spray it again five or six times. My 03 Vulcan had a leak where the PCV valve sits in the grommet and it alomst fell out so get a new grommet and hose and valve. They're dirt cheap.

IAC causing engine to lope at idle so I took off and sprayed inside with CRC MAFS cleaner then sprayed lubed the plunger-shaft and seems to be working OK now. If it cuts up again I have some carb cleaner I'm going to let it soak in for an hour and see if that will eat up deposits in it. Looks clean as a whistle inside but apparently five years & 54K miles have taken their toll on it. Advance wants fifty bucks for it so if I don't get it working right soon I'll replace it. High as the humidity is around here plus salt water nearby, . . I don't see how anything electrical lasts more than two years.

On my 03 I take the intake hose loose at both ends and very easy to get to it like that.
Don't need the special torx screwdriver. Hang in there, be patient and pretty soon that Baby will be purring like a kitten. Pattin' it on the head and tellin' it you love it don't hurt a thing either.

[asalford]

put the new parts on her today and cleared the diagnostic data.

Fuel system went closed loop, the engine idles properly, and all the fuel trim issues are gone. after a week, i'll let ya know if this appears to be a permanent fix. thanks to all who gave me a hand.

[Huney1]

Hang in there, be patient and pretty soon that Baby will be purring like a kitten. Pattin' it on the head and tellin' it you love it don't hurt a thing either.
See there? Wha'd I tell ya'? YYEEAAHH!
Glad you're on the road again and keep us posted on how she percolates.

[asalford]

codes came back, but it will be a while before I can look at it again. It still is running much better. I will continue to investigate.