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Discussion Starter · #1 ·
Sigh...I think I'm on problem 168 after buying this truck and trying to get it roadworthy. Basic info:

96 Bronco
351w E4OD
Rebuilt engine from a 95 Bronco w/1000 miles since rebuild
Currently has CEL for P0172 & P0175 ... bank 1 & 2 running rich

Originally after the engine transplant the vehicle wouldn't start. Eventually traced it to low fuel pressure (28psi). Replaced items affecting pressure (new fuel pump and filter, used regulator). New pressure = 36-39psi and no more lean condition. Truck ran fine for a couple months. During the recent tornadoes in my area, (north Alabama) my wife ran the vehicle completely dry of fuel. She was searching for a gas station that had power when she ran out.

Now...it starts fine and runs fairly well. It stumbles infrequently and smells like its running rich. Once or twice it has died when starting from a dead stop. The fuel pressure still reads >=36 and holds steady during the leakdown test.

I'm hoping someone can point me to something without going all through the FSM again. I'm worn to a nub with this thing right now and would kinda like to just drive it for a change, lol. Any help is appreciated.
 

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I just replaced the fuel pressure regulator on mine and it made the exhaust stink up nasty and it lacked power. You said you put a used one on, it might be bad. Remove the vacuum hose going to the regulator and check if the hose isnt wet=if it is it could be the diaprahm in the regulator is leaking through. Fuel pressure might be good at idle but at on a uphill climb it can change. If it rich, maybe its not getting enough air, make sure there is no obstruction in your intake air system, check you air filter for clogging. Good luck.
 

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A typical autoparts store answer for those two CEL codes it to replace the O2 sensors but I would try everything else first before I did that since they are damned expensive and they generally throw codes because of another problem upstream of the sensors.
 

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I'd try cleaning the MAF sensor then leaving the battery unplugged for 10 minutes to let the computer reset before anything else.
 

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Let us know what you find. Its good to hear feedback/success stories or what not.
 

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Discussion Starter · #8 ·
Didn't get a chance to work on it until today. But.....:rofl:

Cleaned the MAF first and then cleared the codes. Took it for a spin and it's running MUCH better. No stumbling or going dead.

I was checking the O2 sensor voltages while driving and it appeared that the fuel trim was correcting in both directions rather than pegging out in one direction. I was only able to do this for a few minutes because my ebay bluetooth OBD dongle appears to have died.

Thought I would mention that the Bronco has a K & N cone filter on it. This seems to be pretty unpopular with some of the members here. It was on the vehicle when I got it. I don't know if this is contributing to my fuel woes or not.

Thanks again for the help. Maybe I can drive this thing for a few weeks before the next problem...lol.
 

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Didn't get a chance to work on it until today. But.....:rofl:

Cleaned the MAF first and then cleared the codes. Took it for a spin and it's running MUCH better. No stumbling or going dead.

I was checking the O2 sensor voltages while driving and it appeared that the fuel trim was correcting in both directions rather than pegging out in one direction. I was only able to do this for a few minutes because my ebay bluetooth OBD dongle appears to have died.

Thought I would mention that the Bronco has a K & N cone filter on it. This seems to be pretty unpopular with some of the members here. It was on the vehicle when I got it. I don't know if this is contributing to my fuel woes or not.

Thanks again for the help. Maybe I can drive this thing for a few weeks before the next problem...lol.

if that k&n was oiled it could have cause it. thats why i was looking at an oversized aem dryflow.
 

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if that k&n was over-oiled it could have cause it. thats why i was looking at an oversized aem dryflow.
fixed. :thumbup

i've never seen a problem with the oiled k&n air filters. i've had one in my car for 50k miles.

the only way i can see the oil being a problem is if the filter was over-oiled in the first place. MAF sensors need to be cleaned yearly anyway.
 

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fixed. :thumbup

i've never seen a problem with the oiled k&n air filters. i've had one in my car for 50k miles.

the only way i can see the oil being a problem is if the filter was over-oiled in the first place. MAF sensors need to be cleaned yearly anyway.
over oiling them is a pretty well known problem. IF you haven't seen it, it must be because you do not OVER oil yours. :)

Its my understanding that Ford does not have a maintanance recommedation for their MAFs. I have never cleaned mine in a Crown Vic with 190,000 miles on it. Starts right up, runs like a top, still gets 25 mpg highway. I have read that cleaning them is recommened when one uses oiled filters.
 

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over oiling them is a pretty well known problem. IF you haven't seen it, it must be because you do not OVER oil yours. :)

Its my understanding that Ford does not have a maintanance recommedation for their MAFs. I have never cleaned mine in a Crown Vic with 190,000 miles on it. Starts right up, runs like a top, still gets 25 mpg highway. I have read that cleaning them is recommened when one uses oiled filters.
it should be done anyway. clean your throttle plates with some throttle body cleaner, a toothbrush and a rag. then you'll understand why i say to clean the MAF sensor.

it takes 2 minutes. unplug it, take it out, use brake cleaner to spray off the wires in the middle, going from both directions. let dry. install. done.
 

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yo,
For posterity;
MAF Servicing TSB 96-22-5 by Ford for 94-96
ISSUE: The Mass Air Flow (MAF) sensor is not designed to be removed from its body (die-cast or plastic) for servicing. The sensing elements located inside the by-pass tube can be damaged by poking/probing/touching.
ACTION: Service the MAF sensor as an assembly (refer to Figure 1).

Figure 1 - Article 96-22-5
WARNING: DO NOT DISASSEMBLE THE MAF SENSOR.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 203000, 204000, 206000, 607000, 610000, 610500, 611000, 611500, 614000, 614500, 698298

by Ford via miesk5 at cc

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MAF Contamination TSB 98-23-10 for 94-96
Source: by Ford via miesk5 at cc
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.
1. 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.
2. 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.
3. 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.
4. 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.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 206000, 610000, 610500, 610600, 610700, 611000, 611500, 612000, 612500, 614000, 614500, 614600, 698298
-------------------------

P1131 upstream oxygen sensor is not switching rich to lean and back as frequently as it should. This could be due to a vacuum leak, a failing oxygen sensor, or a rich fuel mixture.
Possible Causes are; high fuel pressure, low fuel pressure, restricted fuel filter, engnine misfire, leaking intake manifold gasket, incorrect (stuck open or too cold) engine thermostat, low engine coolant level, restricted air filter, leaking vacuum hoses, or anything else that could affect fuel mixture
 
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