1994 Ford F-150

Tiny
EINSTEIN69
  • MEMBER
  • 1994 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 248,000 MILES
The problem started with the check engine light coming on. I ran the codes it came up 172 O2 sensor lean. I put a new one in, erased the code. Came back on after a few minutes. The truck has been runniing rough, feels like it wants to stall. Driving on the highway, the CEL finally went off. Thats when I started losing power, Stepped on the gas and heard a popping noise. The check engine light came back on, the truck ran fine again. It did this for the trip home. Hooked up fuel pressure guage, all withiin specs. Cleaned the MAF sensor. Could it be the fuel injectors are dirty?
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Tuesday, December 9th, 2008 AT 8:00 AM

9 Replies

Tiny
DAVE H
  • EXPERT
Remove battery terminals. Leave off for at least 5 mins to delete KAM (keep alive memory). Remove and really clean the MAF sensor or replace of course. Re-install MAF. Re-connect battery. The car will will now go through a computer re-learn cycle as you drive it around?

LEAN DRIVEABILITY SYMPTOMS: MAF SENSOR CONTAMINATION
TECHNICAL SERVICE BULLETIN
Reference Number(s): 98-23-10, Date of Issue: November 23, 1998

Related Ref Number(s): 98-23-10
ARTICLE BEGINNING
MASS AIR FLOW (MAF) - SENSOR CONTAMINATION - SERVICE TIP
APPLICATION
Model(s): Ford: 1990-97 Thunderbird
1990-99 Mustang, Taurus SHO
1991-99 Crown Victoria, Escort,
Taurus
1992-94 Tempo
1993-97 Probe
1995-99 Contour
Lincoln-Mercury: 1990-97 Cougar
1991-99 Continental, Grand Marquis,
Sable, Town Car, Tracer
1992-94 Topaz
1993-98 Mark VIII
1995-99 Mystique
Light Truck: 1990 Bronco II
1990-97 Aerostar
1990-99 Ranger
1991-99 Explorer
1994-96 Bronco
1994-97 F Super Duty, F-250 HD
1994-99 Econoline, F-150. F-250 LD,
F-350
1995-99 Windstar
1997-99 Expedition, Mountaineer
1998-99 Navigator
1999 F-250 HD,
Super Duty F Series
Bulletin No: 98-23-10
Date: November 23, 1998
ISSUE
This TSB article is a diagnostic procedure to address vehicles that exhibit lean driveability symptoms and may or may not have any Diagnostic Trouble Codes (DTCs) stored in memory.
ACTION
Follow the diagnostic procedures described in the following SERVICE TIP. The revised diagnostic procedure is a more accurate means of diagnosing the symptoms.
SERVICE TIP
MASS AIR FLOW (MAF) DISCUSSION
MAF sensors can get contaminated from a variety of sources: dirt, oil, silicon, spider webs, potting compound from the sensor itself, etc. When a MAF sensor gets contaminated, it skews the transfer function such that the sensor over-estimates air flow at idle (causes the fuel system to go rich) and under-estimates air flow at high air flows (causes fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows.
If vehicle is driven at Wide Open Throttle (WOT) or high loads, the fuel system normally goes open loop rich to provide maximum power. If the MAF sensor is contaminated, the fuel system will actually be lean because of under-estimated air flow. During open loop fuel operation, the vehicle applies Long Term Fuel Trim corrections that have been learned during closed loop operation. These corrections are often lean corrections learned at lower air flows. This combination of under-estimated air flow and lean fuel trim corrections can result in spark knock/detonation and lack of power concerns at WOT and high loads.
One of the indicators for diagnosing this condition is barometric pressure. Barometric pressure (BARO) is inferred by the Powertrain Control Module (PCM) software at part throttle and WOT (there is no actual BARO sensor on MAF-equipped vehicles, except for the 3.8L Supercharged engine). At high air flows, a contaminated MAF sensor will under-estimate air flow coming into the engine, hence the PCM infers that the vehicle is operating at a higher altitude. The BARO reading is stored in Keep Alive Memory (KAM) after it is updated. Other indicators are Long Term Fuel Trim and MAF voltage at idle.
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Tuesday, December 9th, 2008 AT 9:43 AM
Tiny
EINSTEIN69
  • MEMBER
Removed the MAF sensor, cleaned it. One of the sensors still looks dirty. Should it be replacaed?
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Friday, December 12th, 2008 AT 10:36 AM
Tiny
DAVE H
  • EXPERT
If it look's real bad.I would replace to be on safe side?
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Friday, December 12th, 2008 AT 11:24 AM
Tiny
EINSTEIN69
  • MEMBER
Replaced the MAF sensor. Erased the code. Drove it around, the CEL came back on. How long does it take for the computer to reset?
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Thursday, December 18th, 2008 AT 12:39 PM
Tiny
DAVE H
  • EXPERT
Did you disconnect battery for at least 5 minutes? Did the light come back on straight away? Is it the same code returning?
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Thursday, December 18th, 2008 AT 1:54 PM
Tiny
EINSTEIN69
  • MEMBER
Yes I disconnected it for at least fiive minutes. The CEL came back on after driving the car for about 5 min. It's the same code(172).
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Thursday, December 18th, 2008 AT 2:01 PM
Tiny
DAVE H
  • EXPERT
Try disconnecting battery for 5 mins at least. Disconnect MAF sensor wires. Reconnect battery and test drive this way till engine at normal operating temp? Let me know
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Thursday, December 18th, 2008 AT 2:28 PM
Tiny
EINSTEIN69
  • MEMBER
I did like you said. Drove the truck around after about 10 min. Of driving the CEL came back on. The same code 172. Do I have to keep driving the truck for the CEL to go off. I'm about to drive it to the mechanic so he can get the headache.
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Tuesday, December 23rd, 2008 AT 1:07 PM
Tiny
DAVE H
  • EXPERT
If it has come back on with wires disconnected it can't be the maf sensor setting the fault.

1) Check For Contaminated Engine Oil Turn ignition off. Remove PCV valve from valve cover. Inspect PCV system for damage. Inspect valve for blockage and movement of valve plunger. Repair as necessary. Perform KOEO and KOER SELF-TEST. Service ignition continuous memory code (if present) before KOER codes. If vehicle is a no-start, KOER Code 136, 137, 172, 173 or Continuous Memory Code 139, 144, 171, 175, 176, or 177 is set, install PCV valve and go to next step. If no codes are set, change engine oil and filter. Install PCV valve, and drive vehicle for 5 miles at 55 MPH. Repeat QUICK TEST.
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Tuesday, December 23rd, 2008 AT 2:38 PM

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