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  0bd II codes PO171 & PO174, 2001 ford 150, v6

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Author Topic:   0bd II codes PO171 & PO174, 2001 ford 150, v6
Walter
Junior Member
posted 11-26-2005 08:32 PM     Click Here to See the Profile for Walter   Click Here to Email Walter     Edit/Delete Message   Reply w/Quote
Engine lite on. code scanner reads PO174 & PO171 Bank 1& 2 reading lean. I can't figure out why. Have checked vacume system, egr,MAF, fuel filter, air filter, pvc system
Engines running smooth no misfires gas milage good,

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bks
Member
posted 11-29-2005 02:20 PM     Click Here to See the Profile for bks     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Walter:
Engine lite on. code scanner reads PO174 & PO171 Bank 1& 2 reading lean. I can't figure out why.

Some thoughts:

Scan PCM and look at LTFT. If this number is high (over 15%) The PCM is adding fuel because the engine is lean...or get this, because the engine THINKS it's lean. That means you check the O2 sensors (Pre-catalyst). If the sensors are reporting lean (under 450mV) when the vehicle is indeed running rich, then the sensors are indeed reporting incorrectly and need to be replaced. I enrichen the mixture (dump propane into intake)so I have at least 1% CO Precat and make sure the O2 sensors read over 800mV. If they can't reach that level and the heater circuits are working, then it's time for new sensors.

The MAF sensors on these get dirty all the time, especially if you are trying to run a K&N filter to get the extra couple of ponies.
The oil from the filter coats the MAF hot wire and prevents the PCM from seeing the correct amount of air. This makes the PCM give too little fuel, and then has to add fuel via feedback from the O2 sensors. You can remove and clean the MAF sensor, but use electrical contact cleaner and be very gentle. If I wasn't technically proficient, I would clean the MAF sensor first and see if the problem goes away. At see level the Baro PID on the scanner should read around 158hz. I am not sure how you checked the sensor, so I am still suspicious.....

Your fuel pressure/volume can be too low due to plugged fuel filter, bad regulator or plain bad pump. Check pressure to specs.

You can also have a vacuum leak.

This code does not normally create a misfire or fuel mileage problems, as the system is still controlling itself, it has just reached an adaptive limit....

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Walter
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posted 11-29-2005 08:03 PM     Click Here to See the Profile for Walter   Click Here to Email Walter     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Walter:
Engine lite on. code scanner reads PO174 & PO171 Bank 1& 2 reading lean. I can't figure out why. Have checked vacume system, egr,MAF, fuel filter, air filter, pvc system
Engines running smooth no misfires gas milage good,

Ok let me review what I have done so far: replaced O2 sensors bank 1 & 2, new air filter and new fuel filter, checked pcv valve and lines ( have not done a vacume chek)will have to buy gage 1st, checked egr valve. appears to be working (lines are clean and found no build up or dirt in valve, Checked MAF ( crude method probly full of faults I put an ohm meter across leads and had continuity and then made some jumpers from the maf to the connector so I could check for slight input voltage and a change when rpm was incressed only got slight change. also tried to check for leak in air plennun intake by using either and could not get ghange in RPM.
I know my method is crude and not very reliable but its the best I can do at this time
I do appreciate any and all advice I can get and I will futher check those things yoy recomended...Thanks

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bks
Member
posted 11-30-2005 11:49 AM     Click Here to See the Profile for bks     Edit/Delete Message   Reply w/Quote
The MAF test you indicated is quite inaccurate, clean the MAF and report back.

Also let us know what the BARO reading is before and after if available.

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FIXMALL
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posted 12-14-2005 11:28 PM     Click Here to See the Profile for FIXMALL     Edit/Delete Message   Reply w/Quote
WALTER, JUST HAD SAME SITUATION ON MY FORD TOOK SOME EFFORT TO FIND PROBLEM (cracked pcv hose)BUT USING A STETHASCOPE I COCOULD HEAR THE VACUUM LEAK. REPLACED PCV AND HOSE RESET COMPUTER NO MORE 171&174=

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erick rahzor
Member
posted 12-15-2005 06:12 PM     Click Here to See the Profile for erick rahzor     Edit/Delete Message   Reply w/Quote
usually the heated pcv valve hose in the back is cracked.

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melsa1
Junior Member
posted 12-15-2005 09:38 PM     Click Here to See the Profile for melsa1   Click Here to Email melsa1     Edit/Delete Message   Reply w/Quote
Similar problem possible fix:

Malfunction Indicator Lamp (MIL) on with codes P0171and P0174. Found a Barometric Pressure (BARO) reading on the scan data of 139 Hz, which is extremely low for this elevation (near sea level). Replaced the Mass Air Flow (MAF) sensor, but the BARO reading is still 139 Hz.



Tests: 1. Perform a Keep Alive Memory (KAM) reset with the scan tool, or by disconnecting the vehicle's battery for about 10 minutes. Then recheck the BARO reading. It should then read a default value of around 150 Hz.

2. After resetting KAM, drive the vehicle and perform 4 sustained accelerations at greater than half throttle (obeying local traffic laws, of course). Then recheck the BARO reading to verify that it stayed at or above 150 Hz.



Potential Causes: KAM needs resetting



Tech Tips: BARO reading on scan data at sea level is typically 156 Hz plus or minus 4 Hz, and will go down by about 3 Hz for every 1000 ft above sea level. BARO reading on scan data is NOT a sensor reading, but rather it is a calculation of vehicle elevation that is made by the Powertrain Control Module (PCM). The PCM calculates BARO mainly by looking at the MAF sensor reading at high throttle openings, and comparing the readings to base sea level readings that are stored in internal memory. As such, just cleaning or replacing the MAF sensor will NOT change the BARO reading; the vehicle must be driven at high throttle openings for the BARO reading to recalculate, or it can be reset by disconnecting the battery for about 10 minutes, or performing a Keep Alive Memory reset using a scan tool.



Diagnostic Codes: P0171, P0174







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