Code: Po171
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Senior User
Joined: Feb 2004
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From: FTDIXNJ & BELLE VERNON PA
Code: Po171
I Just Had My 97 Xlt 4x4 4.0 Scanned. It Thru A Po171 Code. This Is Not The First Time. I Have Had My Truck For About 20 Months And I Had This Happen Before. It Cleared Up For About 6-7 Months Now It Is Throwing This Po171 Code Again. Chiltons Say "running Lean". I Have Changed The Maf Awhile Ago Because It Was Sounding Like A Fog Horn. I Also Noticed That Around The Time The Cel Came On It Would Fluctuate In Idle For About 30-45 Seconds. The Temps Have Dropped In The A.m Here In Nj And Thats When I First Noticed It,the First Cool Morning. Any Ideas Before I Start To Replace Stuff? Also One Day I Disconnected The Throttle Position Sensor And It Sort Of Smoothed Out A Bit. Reset The Obd But Eventually Came Back On.the Tech Said Clogged Injector.i Have No Problem With Pick Or Power.any Ideas?
Post Fiend
Joined: Jan 2003
Posts: 9,748
Likes: 16
From: Connecticut
Did you try a search of the archives? These issues have been addressed many times before.
The foghorn sound is usually caused by the IAC, not the MAF. It may sounds like it's coming from down by the MAF area, but it's not.
Have you checked all the vacuum hoses and connections for air leaks? Have you examined the PCV and EGR systems for leaks?
A vacuum/air leak, a misbehaving PCV system, leaky intake gaskets, even an exhaust leak, could all cause an engine to run lean.
Some of the 1997 4.0L's had problems with the fuel supply manifold gasket (not real hard to replace, btw):
Article No. 98-6-8
LIGHT TRUCK: 1997 AEROSTAR, RANGER 4.0L ENGINES ONLY
ISSUE:
A rough idle, stalling at an idle and/or Diagnostic Trouble Codes (DTCs) P0171, P0174, P1131, and/or P1151 may be stored in memory on some vehicles with a 4.0L engine. This may be caused by the gasket located between the fuel rail and lower intake manifold losing its compressive loading and becoming drawn into the intake manifold runners resulting in a vacuum leak.
ACTION:
Replace the fuel rail-to-intake manifold paper gasket with a revised gasket.
....
The foghorn sound is usually caused by the IAC, not the MAF. It may sounds like it's coming from down by the MAF area, but it's not.
Have you checked all the vacuum hoses and connections for air leaks? Have you examined the PCV and EGR systems for leaks?
A vacuum/air leak, a misbehaving PCV system, leaky intake gaskets, even an exhaust leak, could all cause an engine to run lean.
Some of the 1997 4.0L's had problems with the fuel supply manifold gasket (not real hard to replace, btw):
Article No. 98-6-8
LIGHT TRUCK: 1997 AEROSTAR, RANGER 4.0L ENGINES ONLY
ISSUE:
A rough idle, stalling at an idle and/or Diagnostic Trouble Codes (DTCs) P0171, P0174, P1131, and/or P1151 may be stored in memory on some vehicles with a 4.0L engine. This may be caused by the gasket located between the fuel rail and lower intake manifold losing its compressive loading and becoming drawn into the intake manifold runners resulting in a vacuum leak.
ACTION:
Replace the fuel rail-to-intake manifold paper gasket with a revised gasket.
....
Last edited by Rockledge; Oct 29, 2005 at 03:48 PM.
