Guess what!....EMISSIONS ISSUES 96 Cobra

get the exact code.

FUEL SYSTEM MONITOR
Diagnostic Trouble Code Description Possible Causes
P0148 -Fuel Delivery Error At least one bank lean at wide open throttle. Fuel System:
·Severely restricted fuel filter
·Severely restricted fuel supply line

P0171 -System Too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The code is set when the adaptive fuel tables reach a rich calibrated limit. Fuel System:
·Contaminated fuel injectors
·Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
·Vapor recovery system (VMV)
Induction System:
·MAF contamination
·Air leaks between the MAF and throttle body
·Vacuum leaks
·PCV system concern
·Improperly seated engine oil dipstick
EGR System:
·Leaking gasket
·Stuck EGR valve
·Leaking diaphragm or EVR
Base Engine:
·Exhaust leaks before or near the HO2S
·Secondary air concern
Powertrain Control System:
·PCM concern

P0174 -System Too Lean (Bank 2) Same as DTC P0171, but Bank 2. See Possible Causes for DTC P0171

TSB
98-23-10 MASS AIR FLOW (MAF) - SENSOR CONTAMINATION - SERVICE TIP

Publication Date: NOVEMBER 10, 1998

FORD: 1990-1997 THUNDERBIRD
1990-1999 MUSTANG, TAURUS SHO
1991-1999 CROWN VICTORIA, ESCORT, TAURUS
1992-1994 TEMPO
1993-1997 PROBE
1995-1999 CONTOUR
LINCOLN-MERCURY: 1990-1997 COUGAR
1991-1999 CONTINENTAL, GRAND MARQUIS, SABLE, TOWN CAR, TRACER
1992-1994 TOPAZ
1993-1998 MARK VIII
1995-1999 MYSTIQUE
LIGHT TRUCK: 1990 BRONCO II
1990-1997 AEROSTAR
1990-1999 RANGER
1991-1999 EXPLORER
1994-1996 BRONCO
1994-1997 F SUPER DUTY, F-250 HD
1994-1999 ECONOLINE, F-150, F-250 LD, F-350
1995-1999 WINDSTAR
1997-1999 EXPEDITION, MOUNTAINEER
1998-1999 NAVIGATOR
1999 F-250 HD, SUPER DUTY F SERIES


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.

NOTE: THE FOLLOWING PROCEDURE MAY ALSO BE USED TO DIAGNOSE VEHICLES THAT DO NOT HAVE FUEL SYSTEM/HO2S SENSOR DTCs.



Symptoms

Lack of Power
Spark Knock/Detonation
Buck/Jerk
Hesitation/Surge on Acceleration
Malfunction Indicator Lamp (MIL) Illuminated - DTCs P0171, P0172, P0174, P0175 may be stored in memory
OBDII DTCs

P0171, P0174 (Fuel system lean, Bank 1 or 2)
P0172, P0175 (Fuel system rich, Bank 1 or 2)
P1130, P1131, P1132, (HO2S11 lack of switching, Bank 1)
P1150, P1151, P1152, (HO2S21 lack of switching, Bank 2)
OBDI DTCs

181, 189 (Fuel system lean, Bank 1 or 2)
179, 188 (Fuel system rich, Bank 1 or 2)
171, 172, 173 (HO2S11 lack of switching, Bank 1)
175, 176, 177 (HO2S21 lack of switching, Bank 2)
184, 185 (MAF higher/lower than expected)
186, 187 (Injector pulse width higher/lower than expected)
NOTE: DO NOT DISCONNECT THE BATTERY. IT WILL ERASE KEEP ALIVE MEMORY AND RESET LONG TERM FUEL TRIM AND BARO TO THEIR STARTING/BASE VALUES. THE BARO PARAMETER IDENTIFICATION DISPLAY (PID) IS USED FOR THIS DIAGNOSTIC PROCEDURE. ALL OBDII APPLICATIONS HAVE THIS PID AVAILABLE. THERE ARE SOME OBDI VEHICLES THAT DO NOT HAVE THE BARO PID, FOR THESE VEHICLES OMIT THE BARO CHECK AND REFER ONLY TO STEPS 2, 3, AND 4 IN THE DIAGNOSTIC PROCEDURE.



Look at the BARO PID. Refer to the Barometric Pressure Reference Chart in this article. At sea level, BARO should read about 159 Hz (29.91 in. Hg). As a reference, Denver, Colorado at 1524 meters (5000 ft.) altitude should be about 144 Hz (24.88 in. Hg.). Normal learned BARO variability is up to ±6 Hz (±2 in. Hg.). If BARO indicates a higher altitude than you are at (7 or more Hz lower than expected), you may have MAF contamination. If available, Service Bay Diagnostic System (SBDS) has a Manifold Absolute Pressure (MAP) sensor that can be used as a barometric pressure reference. Use "MAP/BARO" test under "Powertrain," "Testers and Meters." Ignore the hookup screen. Connect GP2 to the reference MAP on the following screen.
NOTE: REMEMBER THAT MOST WEATHER SERVICES REPORT A LOCAL BAROMETRIC PRESSURE THAT HAS BEEN CORRECTED TO SEA LEVEL. THE BARO PID, ON THE OTHER HAND, REPORTS THE ACTUAL BAROMETRIC PRESSURE FOR THE ALTITUDE THE VEHICLE IS BEING OPERATED IN. LOCAL WEATHER CONDITIONS (HIGH AND LOW PRESSURE AREAS) WILL CHANGE THE LOCAL BAROMETRIC PRESSURE BY SEVERAL INCHES OF MERCURY (±3 Hz, ±1 in. Hg.).



NOTE: BARO IS UPDATED ONLY WHEN THE VEHICLE IS AT HIGH THROTTLE OPENINGS. THEREFORE, A VEHICLE WHICH IS DRIVEN DOWN FROM A HIGHER ALTITUDE MAY NOT HAVE HAD AN OPPORTUNITY TO UPDATE THE BARO VALUE IN KAM. IF YOU ARE NOT CONFIDENT THAT BARO HAS BEEN UPDATED, PERFORM THREE OR FOUR HEAVY, SUSTAINED ACCELERATIONS AT GREATER THAN HALF-THROTTLE TO ALLOW BARO TO UPDATE.



BAROMETRIC PRESSURE REFERENCE
Barometric Pressure (in. Hg.) Barometric Pressure (kPa) BARO/MAP PID (Hz) Altitude above sea level (ft)
3.5 11.8 89.3
5 16.9 92.8
10 33.8 104.6
15 50.7 117.0 14,000
20 67.5 129.6 10,000
21 70.9 132.5 9,000
22 74.3 135.4 8,000
23 77.7 138.3 7,000
24 81.1 141.1 6,000
25 84.4 144.0 5,000
26 87.8 146.9 4,000
27 91.2 149.8 3,000
28 94.6 152.8 2,000
29 97.9 155.8 1,000
30 101.3 158.9 0 (sea level)
31 104.7 162.0
31.875 107.7 164.7



On a fully warmed up engine, look at Long Term Fuel Trim at idle, in Neutral, A/C off, (LONGFT1 and/or LONGFT2 PIDs). If it is more negative than -12%, the fuel system has learned lean corrections which may be due to the MAF sensor over-estimating air flow at idle. Note that both Banks 1 and 2 will exhibit negative corrections for 2-bank system. If only one bank of a 2-bank system has negative corrections, the MAF sensor is probably not contaminated.
On a fully warmed up engine, look at MAF voltage at idle, in Neutral, A/C off (MAF V PID). If it's 30% greater than the nominal MAF V voltage listed in the Powertrain Control/Emissions Diagnosis (PC/ED) Diagnostic Value Reference Charts for your vehicle, or greater than 1.1 volts as a rough guide, the MAF sensor is over-estimating air flow at idle.
If at least two of the previous three steps are true, proceed to disconnect the MAF sensor connector. This puts the vehicle into Failure Mode and Effects Management (FMEM). In FMEM mode, air flow is inferred by using rpm and throttle position instead of reading the MAF sensor. (In addition, the BARO value is reset to a base/unlearned value.) If the lean driveability symptoms go away, the MAF sensor is probably contaminated and should be replaced. If the lean driveability symptoms do not go away, go to the PC/ED Service Manual for the appropriate diagnostics.
NOTE: DUE TO INCREASINGLY STRINGENT EMISSION/OBDII REQUIREMENTS, IT IS POSSIBLE FOR SOME VEHICLES WITH MAF SENSOR CONTAMINATION TO SET FUEL SYSTEM DTCs AND ILLUMINATE THE MIL WITH NO DRIVEABILITY CONCERNS. DISCONNECTING THE MAF ON THESE VEHICLES WILL, THEREFORE, PRODUCE NO IMPROVEMENTS IN DRIVEABILITY. IN THESE CASES, IF THE BARO, LONGFT1, LONGFT2, AND MAF V PIDs INDICATE THAT THE MAF IS CONTAMINATED, PROCEED TO REPLACE THE MAF SENSOR.



After replacing the MAF sensor, disconnect the vehicle battery (5 minutes, minimum) to reset KAM, or on newer vehicles, use the "KAM Reset" feature on the New Generation Star (NGS) Tester and verify that the lean driveability symptoms are gone.

T
hat's good stuff right there.

Could be a vacuum leak. I had a similar problem when I headswapped my '98.

It kept throwing P0171 and P0174 for a period of about 8 months. We tried everything to nail it down. Checked vacuum lines, check MAF, replaced PVC, installed a new dipstick, everything.

We read the long term fuel trims on numerous occasions with WDS and the condition only existed at idle and just off idle, so we were pretty much damn sure it was some sort of a vacuum leak that smoothed out with throttle application.

We finally decided that we were going to replace the intake gaskets, thinking that the problem was most likely caused during the swap. We were partially right.

As a last shot at an easy fix, we replaced the EGR gasket. Bingo, problem solved. When we swapped car we didn't disconnect the EGR valve all the way, we just pulled it back when we moved the plenum. This damaged the gasket and caused a MAJOR annoyance for what was pretty easy fix ($5 part.)

Perhaps it is possible that the EGR gasket was not replaced, or was improperly installed, when the shorties were installed. I'd definitely hunt for a vacuum leak before you continue to replace sensors. You can use a can of carb cleaner and spray it on your vacuum lines, carefully, and listen for idle surges to determine if that is the cause.

Those codes can be a bear to diagnose, but persistence pays off (it only took us 8 months!)

Good luck.