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Old 05-28-2011, 19:34   #1 (permalink)
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2001 f150 4.2L P0171 & 174

Checked for vacuum leaks.
Nothing.
Replaced MAF sensor, but both codes came right back.
Normally a MAF solves this one, but not this time.
Any other suggestions?
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Old 05-28-2011, 20:50   #2 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

How about the PCV Are there any exhaust leaks? How is the fuel pressure? Does it run good otherwise? What kind of driving did you do for the codes to come back?
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Old 05-28-2011, 21:20   #3 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

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How about the PCV Are there any exhaust leaks? How is the fuel pressure? Does it run good otherwise? What kind of driving did you do for the codes to come back?
I checked with carb cleaner for leaks. Kind of old fashioned way to do that, but I don't have real scanner to watch fuel trims. Didn't notice any idle change at all. I can't hear any exhaust leaks. It's not my truck, so I did not drive it at all, but the owner uses the truck just for normal street driving.
It runs fine, I am told. No stalls or stumbles. Started up and ran fine sitting in my driveway.
The codes came back within an hour after changing the MAF and clearing the PCM.
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Old 05-29-2011, 07:27   #4 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

It could be a vacuum leak in the MAF to throttle body hoses when the engine flexes.
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Old 05-29-2011, 14:53   #5 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

Just got the truck back over here. I double/triple checked this thing for any signs of vac leak or pcv problems and I can't find any. The boot to the throttle body is fine. The new MAF purchased at Orielly looks like it has been on another car already so it is being exchanged for another one, and we are also going to put a new fuel filter on there. We'll know in a couple hours if the problem comes back.
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Old 05-29-2011, 16:26   #6 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

Good luck, keep us posted.
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Old 05-29-2011, 16:43   #7 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

Well, that didn't take long.
The 2nd replacement sensor made no difference at all.
The light came on within 10 minutes.
Same 2 codes.
Put a new fuel filter on afterwords, but I am not confident that will do any good for this problem.
I'm stumped.
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Old 05-29-2011, 19:17   #8 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

Here's a link to something that may help. http://sites.google.com/site/fordf15...P0171P0174-Fix
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Old 05-30-2011, 20:41   #9 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

I think those are cylinder miss codes for #1 and #4
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Old 05-30-2011, 20:48   #10 (permalink)
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Re: 2001 f150 4.2L P0171 & 174

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I think those are cylinder miss codes for #1 and #4
They are "system lean" codes.
P03XX are the misfire codes.
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