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Code P0171 Lean bank 1 (already seached)

26K views 37 replies 15 participants last post by  99graveyard  
#1 ·
My 96 OBD II, 351 is showing a lean bank 1 code.

I Checked for vacuum leaks and checked vacuum at Idle it was around 21 in/Hg.

I checked the fuel pressure key on engine off 40psi, fuel pressure engine running is 31psi

Also pulled the vacuum hose off of the EGR valve while it was running, no change in the idle as it is idling slightly rough already.

It revs smooth and has power under load.

Any one have any Ideas as to what it could be.

Of the threads I have read it seems it's usually a vacuum leak or a fuel delivery issue.

Not sure what my next step should be.
 
#2 · (Edited)
yo;
DTC P0171 - System to Lean (Bank 1); "... The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit.
For lean and rich DTCs:
Fuel system Excessive fuel pressure.
Leaking/contaminated fuel injectors.
Leaking fuel pressure regulator.
Low fuel pressure or running out of fuel.
Vapor recovery system.
Induction system:
Air leaks after the MAF. Check MAF for contamination; see below)
Vacuum Leaks.
PCV system.
Improperly seated engine oil dipstick.
EGR system: Leaking gasket. Stuck EGR valve. Leaking diaphragm or EVR. SEE BELOW for TESTING
Base Engine: Oil overfill. Cam timing. Cylinder compression. Exhaust leaks before or near the HO2Ss

Test & Overview, W/Differential Pressure Feedback (DPFE) Sensor
by Mike N at smpcorp.com via web.archive.org
SLOW TO LOAD, so I'll give you the text here;
MIESK5 NOTE: only 95 5.8L California models & all 96 have the DPFE Sensor instead of EGR Valve Position Sensor (EVP) & Trucks never used a Pressure Feedback Exhaust (PFE) Sensor
"...The first step is to perform a thorough visual inspection of the system. If the inspection reveals nothing obvious, then some diagnostics are in order. Install a vacuum gauge in the vacuum line between the EGR valve and the control solenoid. Next, run the Key On-Engine Running self test. At one point during the self test, the PCM will check the EGR system by applying vacuum to the EGR valve. It accomplishes this by grounding the EGR regulating solenoid at a duty cycle of approximately 30%. If you see that the vacuum gauge indicates a vacuum reading of a few inches or more, you can be sure that the PCM, wiring, vacuum lines, and the regulating solenoid are functional. If not, then you must investigate where the source of the problem lies. If you do get a vacuum signal, then, exit the self test. With the engine at idle, apply vacuum to the EGR valve with a vacuum pump. When you apply vacuum, you should notice a change in engine RPM, with the possibility that the engine may stall. If the engine RPM changes, then we know the EGR is working. If there are no changes, then either the EGR valve is not functioning, or, the EGR passages are blocked with carbon. If engine RPM does change, then our next step is to examine the PFE (Pressure Feedback) or DPFE (Differential Pressure Feedback) sensor. Some early systems use a single hose sensor called the PFE sensor, while others use the DPFE sensor. Both sensors have three wires. The three wires consist of a 5 volt reference (which is shared with other sensors), a sensor ground (which is also shared), and a dedicated signal or output wire which is connected to the PCM. The PFE sensor measures exhaust gas pressure, while the DPFE sensor measures the difference between the upstream pressure (exhaust side), and the downstream pressure (intake side). Both sides are separated by an orifice assembly which is a calibrated opening that exhaust gas flows through when the EGR valve opens (refer to diagram #1). The DPFE sensor should measure equal pressure on both sides with the EGR valve closed. This means that we can measure and compare the signal voltage at idle with the signal voltage at key on, engine not running. Under these two conditions, if we see a difference in voltage output, then the EGR valve must be open (normally it should not be open at idle, or, with the engine not running). When the EGR valve opens under normal conditions, the upstream pressure should begreater than the downstream pressure. If not, then one of the hoses of the sensor is either off or plugged, or the orifice is blocked. The signal of the DPFE sensor at idle ranges from .20 to .90 volts DC. The actual voltage will vary depending upon the vehicle. Any voltage reading that is out of that range at idle will usually set a fault code. A fault code will also set if the PCM does not see a sufficient voltage change when EGR operation is commanded. Testing of the DPFE sensor can be done by monitoring its output voltage while applying vacuum to the EGR valve. If you notice an RPM change, or, the engine stalls, and the output voltage does not change, then the sensor is suspect. This assumes that the reference voltage and ground circuits are good. Also, tap on the sensor LIGHTLY to see if the output voltage changes. If the output changes, then the sensor is suspect. Typical output voltage on a PFE sensor with "Key ON, Engine OFF", or, with no EGR command is 3.20 to 3.30 volts DC. The voltage signal should increase when vacuum is applied, and decrease when pressure is applied. The DPFE’s output voltage with "Key On, EngineOff" is between .30 and .60 volts DC. This figure is applicable to the sensor with the aluminum housing. Look for an output voltage that’s about .2 to .3 volts higher for the sensor with the black plastic housing. If you apply vacuum to the EGR valve with the engine at idle, you should notice a change in the sensor’s output voltage, as well as some change in the idle RPM. The common causes of sensor failure are contamination, and excessive exhaust backpressure. Contamination can be caused by exhaust by-products as well other problems such as coolant from a failed gasket. Moisture from condensation can also present problems. One final note about all EEC V OBD II systems: the EGR system will not set any codes as long as the ambient temperature sensor "sees" the temperature below 32°F. Under these conditions, it is likely that if condensation has occurred, it will freeze and create some type of problem..."

....
Test, Vacuum Video in a 96 5.0, using a hand-held vacuum pump/gauge
Source: by Tony K (Boat Dude, Big Blue) at SuperMotors.net

....
for the hand-held vacuum pump/gauge, if you don't have or can borrow one from pals, ck out AZ's LOAN-A-TOOL® PROGRAM
Vacuum Pump, Gauge reads 0 to 30 inches of mercury. All aluminum construction with reverse pistol grip for easy one-handed operation. One 24 inch piece of clear plastic tubing included with pump. OEM27010.. they placed it under Valve Train Repair for some reason..lol



==========

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.
Image

ACTION: Service the MAF sensor as an assembly (refer to Figure 1).
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 http://web.archive.org/web/20110704...nical_service_bulletins.htm#Door, Side, Wind Noise TSB 99-6-5 by Ford for 94-96
I'd clean it anyway


More MAF Info LINKs:
including; Cleaning, in a F 150
Source: by Dan N @ http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php

&

MAF Contamination TSB 98-23-10 for 94-96 Source: by Ford via miesk5 at cc[/URL]
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
-------------------------

Long shot is a bad DPFE Sensor
Testing in a 96 5.0; "...DPFE comes in as .15 VDC during KOEO test between REF & Ground. TOMCO says it should read 0.45 +/- 0.25 volts for the .55 volt for this original Aluminum type sensor My Ford PCED/EVTM is frozen, so I can't view Ford's +/- values. &, when pulling REF hose off, fine particles fell out of DPFE. So, figuring DPFE Sensor is bad according to Ref voltage and particles... Yes, your voltage of 0.15V on the DPFE line is a typical sign of a bad one. Try to obtain a Motorcraft replacement, as the retail part store pieces don't last..."
Source: by SigEpBlue (Steve) & miesk5 at FSB

Testing & Vacuum/Voltage Parameters & pics on both older Aluminum & Newer Plastic Version; miesk5 Note, Tomco Figure 4 for Plastic Housing version, it shows +/- 0.25 volts; It should be 1.0 +/- .025 volts as desribed in the narrative and in Ford EVTM; "...Access DPFEGR PID (formerly DPFE) with a Scan Tool. PID voltage should be 0.2-1.3 volts..."
Source: by tomco-inc.com @ http://web.archive.org/web/20110704111721/http://www.tomco-inc.com/Tech_Tips/ttt36.pdf

Testing in a 96 5.0; "...DPFE comes in as .15 VDC during KOEO test between REF & Ground. TOMCO says it should read 0.45 +/- 0.25 volts for the .55 volt for this original Aluminum type sensor My Ford PCED/EVTM is frozen, so I can't view Ford's +/- values. &, when pulling REF hose off, fine particles fell out of DPFE. So, figuring DPFE Sensor is bad according to Ref voltage and particles... Yes, your voltage of 0.15V on the DPFE line is a typical sign of a bad one. Try to obtain a Motorcraft replacement, as the retail part store pieces don't last..."
Source: by SigEpBlue (Steve) & miesk5 at http://fullsizebronco.com/forum/21-...-bronco-tech-questions-flame-free-zone/146687-dpfe-hose-source-ref-voltage.html
 
#8 ·
Id like to mention that if it was a leak on the main intake then both banks would be lean, not just the first one. the only way it can be a leak is if the leak is right next to one of the cylenders on that bank. Id do a power balance and then an injector balance test.
 
#11 ·
Id like to mention that if it was a leak on the main intake then both banks would be lean, not just the first one. the only way it can be a leak is if the leak is right next to one of the cylenders on that bank. Id do a power balance and then an injector balance test.
which is exactly how it can have a lean code for only one bank, even if the intake plenum gasket is what's leaking. if it's only leaking on a runner for a cylinder on bank 1, it's only going to throw a code for that bank.

there's really not much that differs vacuum wise from side to side. it's not like the EGR dumps into bank 1, while the brake booster get's it's vacuum from bank 2.
 
#12 ·
My bet is that it is the oxygen sensor on that side. Look at Miesk5's entry again. Probably not really lean, but the sensor thinks that side is lean.
 
#13 ·
yo,
Since MAF and MAF/intake tubes leaks are now discounted;
I go w/rla2005 on PCV:

Check PCV/ line for;
PCV hose or elbow collapsed PCV valve Info & pic, 1 port vs. 2 port for 5.0; "...That's a genuine Ford PCV valve. It's stock two port top (top of pic); makes it difficult to fit under the upper intake on an EFI 5.0 engine. Buy an aftermarket single port(lower in pic) and use the top on the Ford PCV..." miesk5 Note, often the rubber cap on the top port pops off

Source: by Sixlitre (Malcolm H, Eddie Bauer) at SuperMotors.net
PCV hose vacuum leak (s)- use short section of garden hose to use as a stethoscope to listen for the leak(s); or on COLD ENGINE only, use propane torch w/rubber hose attached, UNLIT or spray carb cleaner, when it gets to the the leak the RPMs will rise
 
#14 ·
Lean code is gone pretty sure it was the disconnected valve cover vent.

Now I have a miss fire on cylinder 4.

I changed all of the plugs, that didn't help the missfire. The plug wires are fairly new ford motorsport wires. what should the resistance be on the plug wires.

Also what should the reading be from the O2 sensors at idle. I am looking at live data through my scan tool the values coming back from the O2 sensors are all over the place.

The scan tool is also showing that my heater, O2sensor and Cat monitors haven't cleared. That's why I am wondering about the O2 sensor values.
 
#15 ·
Lean code is gone pretty sure it was the disconnected valve cover vent.
Was the hole on the air intake plugged?

Now I have a miss fire on cylinder 4.

I changed all of the plugs, that didn't help the missfire. The plug wires are fairly new ford motorsport wires. what should the resistance be on the plug wires.
Put a calibrated ignition tester on the end of the number 4 wire.
If the spark is healthy and consistant then do a fuel injector balance test.


Also what should the reading be from the O2 sensors at idle. I am looking at live data through my scan tool the values coming back from the O2 sensors are all over the place.
Thats normal. They fluctuate very fast but range will stay pretty consistant.

The scan tool is also showing that my heater, O2sensor and Cat monitors haven't cleared. That's why I am wondering about the O2 sensor values.
Manually clear the codes with the scan tool. Then run it and see if they come back. If your O2 sensor heater is bad the sensor has to be replaced.
 
#16 ·
Was the hole on the air intake plugged?


Put a calibrated ignition tester on the end of the number 4 wire.
If the spark is healthy and consistant then do a fuel injector balance test.



Thats normal. They fluctuate very fast but range will stay pretty consistant.


Manually clear the codes with the scan tool. Then run it and see if they come back. If your O2 sensor heater is bad the sensor has to be replaced.
It had some kind of rigged cold air intake. So there was no where for it to go the PO just put a small filter on it.

I put a stock air box setup back on it.

I will try the spark tester.


How do you do an injector balance test?

Are the injectors on a 93 the same as a 96. I have a 93 parts truck with a complete set of injectors on it.

Just wondering in case I have a bad injector.
 
#17 ·
It had some kind of rigged cold air intake. So there was no where for it to go the PO just put a small filter on it.

I put a stock air box setup back on it.
If there wasnt a hole in the intake stream then it wouldnt cause a lean condition. It probably had a leak around a fitting or something.




How do you do an injector balance test?
The scantool should be able to do it. It fires each injector for a certain amount of time and you measure how much the pressure drops with a gauge. All of them should be within like 2% of each other. If one doesnt drop much or at all then its clogged.

Are the injectors on a 93 the same as a 96. I have a 93 parts truck with a complete set of injectors on it.
:shrug
Id think so.
 
#20 ·
P0171/P0174...Lean Condition banks 1 & 2 ('96 302/E4OD)

Been running a CEL for about a month now on my '96 302. AutoZone scanned and told me I had both the above the codes for Lean Condition Left and Right. The engine did have a little trouble starting with this condition (e.g., a little excessive cranking,) but once it lit, it ran like a top.

I thought it was my custom intake system (using the Advanced Air Cleaner Systems off road filter) with it's multitude of elbows and adapters/clamps, but after a second check, everything looked tight, and no apparent vacuum leaks or sucking air sounds. :scratchhe:

My local Ford Service department called today and said it was a bad fuel pump...which was actually my second guess if only because the fuel pump has been whining and whirring like a small turbine back there for well over a year. Figured one day I wouldn't hear the pump and it would just not start...but I got the CEL first.

Just slightly under $700 for labor and materials. Cha-ching.
 
#25 ·
Been running a CEL for about a month now on my '96 302. AutoZone scanned and told me I had both the above the codes for Lean Condition Left and Right. The engine did have a little trouble starting with this condition (e.g., a little excessive cranking,) but once it lit, it ran like a top.

I thought it was my custom intake system (using the Advanced Air Cleaner Systems off road filter) with it's multitude of elbows and adapters/clamps, but after a second check, everything looked tight, and no apparent vacuum leaks or sucking air sounds. :scratchhe:

My local Ford Service department called today and said it was a bad fuel pump...which was actually my second guess if only because the fuel pump has been whining and whirring like a small turbine back there for well over a year. Figured one day I wouldn't hear the pump and it would just not start...but I got the CEL first.

Just slightly under $700 for labor and materials. Cha-ching.

your code was for left and right, The original posters was for left bank lean. both of which are different. If it was his fuel pump he should be tossing a lean code on both banks.
 
#21 ·
fuel pumps are almost NEVER a cause for a lean code. shit, fuel issues are almost never a lean condition problem. 90% of the time it's a vacuum leak.

if you just dropped $700 for a pump, you have been had.
 
#22 ·
I beg your pardon?



Ummmmm, really? So, since you said "Almost never..." and "90% of the time..." I went ahead and did the math. According to your statistics, there is still what... a 10% chance, correct...or is my math wrong? And why wouldn't a low pressure fuel delivery issue be one of the initial checks you make for a lean condition on the left and right banks? Sure, you start by checking the obvious: a vacuum leak. But when my '96 fuel pump has been whining for the last year or so, it really kinda' make sense. Oh, and after multiple web searches for "P0171/P0174", including here at this august web site...each search result consistently mentioned three causal factors for P0171/P0174: Vacuum leak, dirty MAF, and low fuel pressure (e.g., clogged fuel filter, bad pump, dirty injectors, etc...)

Looking back, nothing has changed in the engine compartment. I have yet to see any gremlins crawling under the hood and cutting vacuum lines or the like. I even checked and re-checked the intake tubes, vacuum lines, and related intake tubing before taking it to the dealer. No issues. It's been driving great since the 'Sixlitre tune-up,' and even drove great while the CEL light was on. But hey, I will get a full 1 year warranty on the new fuel pump and if the CEL goes away, it runs like a champ, and passes my upcoming smog test here next month, then I'm good with that.

If however, the pump replacement does not resolve the issue, then I can get it corrected and apply my $700 towards further diagnostics and repair. I'm good with that too. The onus is on the dealer.

So, your comment about me being "had," ....yeah, not so much.

In fact, unsolicited responses from various 'senior' members (and know-it-alls) of FSB (like your response above) is a perfect example of why a lot of us have left this site and moved on (and over to www.gofastbroncos.com.) No idiot treatment there.

(The mere fact that this FSB website has a dedicated forum that is "Flame Free" speaks volumes.)
 
#26 ·
For future people that might read this thread, just solved the same issue on my 1990, non-maf, single o2 sensor on right side, the truck would never know if both sides are lean, but still.. it was a simple fix, exhaust manifold bolts came loose, snugged them up and it was fine.
 
#29 · (Edited)
End of story...

OK, lets close this melodrama out with some facts...with my humble apologies to the OP:

  • Vacuum test: OK
  • Visual inspection of fittings, hoses, clamps: OK
  • Fuel pressure tests: Confirmed 28 PSI at Idle and 28 PSI @ high RPM (no corresponding pressure increase upon engine load/RPM increase)
  • Factory fuel pump pressure specs: 35-45 PSI (35 @ idle, 45 at higher RPMs)
  • Replaced: Fuel Pump
  • Fuel pressure re-test results: 35 PSI @ idle, 42 PSI @ high RPM
  • Codes: Cleared
  • No more CEL
  • Seat of the pants testing: Noticeable improvement of engine response at highway speeds and while accelerating in traffic; immediate start up hot or cold (starting had been problematic for the last year since I did my Sixlitre tune-up...never could figure out why...I thought it was the 13.5* advance was causing some cranking issues)
  • End of story
  • Your mileage may vary...
  • Oh yeah, the fuel pump is quiet as a mouse... :clap
 
#32 ·
Still working on my issues with my 96. Which side is bank 1 and which side is bank 2? Its throwing random codes for lean bank 1 to hego slow to respond bank 2 to some other kinda lean something......question along with this is would this also cause 1 side of the motor on a manual temp gauge to run hot but the computer to read the otherside running at 176-185? The truck is still doin this after sittin 11months through my deployment and a dead battery.
 
#33 ·
Still working on my issues with my 96. Which side is bank 1 and which side is bank 2?
Bank 1 is passenger side/side with #1 cylinder.

Its throwing random codes for lean bank 1 to hego slow to respond bank 2 to some other kinda lean something......question along with this is would this also cause 1 side of the motor on a manual temp gauge to run hot but the computer to read the otherside running at 176-185? The truck is still doin this after sittin 11months through my deployment and a dead battery.
Can you elaborate on the "Manual" temp gauge vs Computer?

There are two sensors for coolant temp. 1 is for the gauge and the other is for the Comp. Each have different voltage/resistances.

As mentioned way before, check for vacuum leaks, fuel pressure and MAF sensor is good.

KC
 
#34 ·
I took the manual gauge sensor out and replaced it with an aftermarket non electrical gauge cause I thought the gauge was screwing up. So the ds of the motor runs hot while the ps where the ecu reads from runs a nice normal temp. But it keeps throwing the lean codes for the ps.
 
#36 ·
So you're saying you have an accurate gauge, what are you saying is "hot" for the motor. Normal is 190-205 +- 5*

I would imagine if its only reading bank one lean, check for vac leaks around the intake runners and I second this:
Often the lean bank codes will not appear until there is a load on the motor. If the motor has all the stock connections unlike the original problem of this thread then diagnose a bad fuel pump or regulator by an on the road fuel pressure test. Watch the gauge and see what happens to the pressure. Low pressure means lean mixture.
PW
Check the FP at idle, then ziptie the pressure guage on the wiper going down the road to see what it is at cruze/accel/WOT.

KC
 
#35 ·
Often the lean bank codes will not appear until there is a load on the motor. If the motor has all the stock connections unlike the original problem of this thread then diagnose a bad fuel pump or regulator by an on the road fuel pressure test. Watch the gauge and see what happens to the pressure. Low pressure means lean mixture.
PW
 
#38 ·
I had the lean at part throttle code and my bronco would buck a little at first then pretty bad.. I disconnected the egr vacuum line and bam. No more bucking. The computer doesn't cut the fuel expecting recirculating exhaust and gas to reenter because the egr sensor says it's closed. Takes 10 secs and worth a try. I taped the vacuum hole up until I can/want replace my egr tube.

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