NEED HELP P0171 on my 04 Trailblazer LT won't go away

[ghost_leader07]

UPDATE:

I was checking my catalytic converter as per @budwich suggestion and I believe my cat is clogged but it's better for you guys to take a look at the data I've gathered so far:

My live data @ idle:



@ Idle O2 Sensors and Fuel Trims data

Short Drive in Traffic data

I did an additional test on my cat using a infrared thermometer while the truck at operating temperature right after my drive and the readings were:

Inlet pre cat: 203°C (397.4°F)
outlet post cat: 192°C (377.6°F)

this is enough evidence that my cat is clogged/bad?

 

[mrrsm]

Just in case this Professional Mechanic VOP (Video Original Poster) covers any new ground for this P0171 investigation, have a look at what he does here in parallel to your own considerable efforts.

He adds in confirming information on 'what to look for' with your Short Term Fuel Trim Values that will ultimately square away the LTFT Values with additional Drive Cycles in the event you finally manage to corner this Mysterious P0171 Critter.

The Scanners the VOP Demos here is also a subliminal suggestion that it might be time to get yourself either a "GYMKO" (General Motors Knock Off) Tech 2 Scan Tool Kit for around $300.00 via AliExpress.com Vendors ...or perhaps one of the Better Scanners stateside that also cover the 2013 and Later Model GM-GMC Vehicles:

 

[ghost_leader07]

Just in case this Professional Mechanic VOP (Video Original Poster) covers any new ground for this P0171 investigation, have a look at what he does here in parallel to your own considerable efforts.

He adds in confirming information on 'what to look for' with your Short Term Fuel Trim Values that will ultimately square away the LTFT Values with additional Drive Cycles in the event you finally manage to corner this Mysterious P0171 Critter.

The Scanners the VOP Demos here is also subliminal suggestion that it might be time to get yourself either a "GYMKO" (General Motors Knock Off) Tech 2 Scan Tool Kit for around $300.00 via AliExpress.com Vendors ...or perhaps one of the Better Scanners stateside that also cover the 2013 and Later Model GM-GMC Vehicles:

Thanks for the suggestion,

I've watched this video before and wish my issue was that simple, i'm currently investigating a possible clogged cat on my truck maybe you can check the data i've posted in moments ago and tell me what do you think of my cat performance.

your help is much appreciated.

 

[Mooseman]

With the evidence from the post cat O2 sensor and the temps , it is pretty much conclusive that the cat is dead but not necessarily clogged.

 

[budwich]

I didn't say you had a clogged cat... I said it might be damaged IF you have been running rich for a long time. The "waggle" on the downstream at various points seems less where there is "steady state" throttling. Overall, something has changed in your testing as the displays for temperature seems correct / stable and o2 sensors are functioning. what happened?

There is a PID for cat temperature.... somewhere in the list.

Your trims seem relatively "stable" although negative leaning (ltft). The display update (dial) may not be fast enough to capture any short term "glitches" that graphing might show... I believe you can select the same "mini graph dial" that you are showing for o2 sensors... but maybe not... I haven't tried that. Having said this, when was the last time your code (p0171) appeared?

On the MAP sensor, the pid might be something absolute intake manifold air pressure (psi).... you appear to be using the equivalent for kpa (although there might be an A and B which I don't know what the difference is). Have you checked the seal area around the MAP to ensure that it is good both on the intake and the knub of the sensor?

 

[ghost_leader07]

I didn't say you had a clogged cat... I said it might be damaged IF you have been running rich for a long time.

Sorry i meant to say insufficient/damaged cat but it could be partially clogged 'cause i took my truck for a ride and I've noticed somewhat sluggish acceleration and a bit jittery before shifting it's quite noticable at WOT which i did twice and make sure, but I won't try WOT again.

The "waggle" on the downstream at various points seems less where there is "steady state" throttling. Overall, something has changed in your testing as the displays for temperature seems correct / stable and o2 sensors are functioning. what happened

It appears that my ECU was still collecting data after clearing the fault codes and before checking with my elm device now both of my o2 sensors are giving me somewhat steady readings but still experiencing the strange engine coolant temperatures but it's less frequent.

I've yet to go to the auto shop for scan (having a busy week)

Your trims seem relatively "stable" although negative leaning (ltft). The display update (dial) may not be fast enough to capture any short term "glitches" that graphing might show... I believe you can select the same "mini graph dial" that you are showing for o2 sensors... but maybe not... I haven't tried that.

Yeah i can change it to graph display I'll check and send you the chart.

Having said this, when was the last time your code (p0171) appeared?

I've cleared it about 30 miles ago but i came home today and i saw my rpm jump up to 900rpm with p017 pending code, I've noticed that if i drive really slow like around 20mph it's more likely to trigger the code i remember last time I drove it on the highway at 80-90mph for a long distance trying to get it to appear but I didn't but it did come on the next day after driving slow in traffic.

On the MAP sensor, the pid might be something absolute intake manifold air pressure (psi).... you appear to be using the equivalent for kpa (although there might be an A and B which I don't know what the difference is)

The intake is the PID for Intake pressure sensor measure at kPa but i can switch it psi, what's the normal psi for the MAP on idle and while driving

Have you checked the seal area around the MAP to ensure that it is good both on the intake and the knub of the sensor?

I've tried to wiggle it around to see if it's loose but it's seems to be tight, should i spray anything around the seal tp check for leaks? Perhaps some water? I don't think it's wise for me to using crab cleaner there

 

[ghost_leader07]

With the evidence from the post cat O2 sensor and the temps , it is pretty much conclusive that the cat is dead but not necessarily clogged.

Thanks @Mooseman I'll straight pipe it for now and I'll be getting a replacement later.

 

[budwich]

quote: "The intake is the PID for Intake pressure sensor measure at kPa but i can switch it psi, what's the normal psi for the MAP on idle and while driving".... somewhere in the 16-20 range at idle... quite a bit lower at constant medium throttle.

quote: "I've noticed that if i drive really slow like around 20mph it's more likely to trigger the code i remember last time I drove it on the highway at 80-90mph for a long distance trying to get it to appear but I didn't but it did come on the next day after driving slow in traffic." change your air filter.

 

[budwich]

quote: "The intake is the PID for Intake pressure sensor measure at kPa but i can switch it psi, what's the normal psi for the MAP on idle and while driving"...
I went back thru my torque setup and found that the pid used for monitoring vacuum by the MAP is called turbo boost and vacuum gage. It is a standard pid not a GM extension so you should see it the list of displayable values when adding a gage. It gives the value in/hg which as I indicated at idle should be 16-20. further, with the key off, it should provide some "relative value" for your "barometric pressure" depending on your altitude if I understand the operation. sorry I wasn't more specific... I had set this up a long while ago and thought the parameter was more specifically identified as absolute manifold air pressure.

 

[ghost_leader07]

quote: "The intake is the PID for Intake pressure sensor measure at kPa but i can switch it psi, what's the normal psi for the MAP on idle and while driving"...
I went back thru my torque setup and found that the pid used for monitoring vacuum by the MAP is called turbo boost and vacuum gage. It is a standard pid not a GM extension so you should see it the list of displayable values when adding a gage. It gives the value in/hg which as I indicated at idle should be 16-20. further, with the key off, it should provide some "relative value" for your "barometric pressure" depending on your altitude if I understand the operation. sorry I wasn't more specific... I had set this up a long while ago and thought the parameter was more specifically identified as absolute manifold air pressure.

Thanks for the follow-up, I'll try this today and keep you updated.

 

[ghost_leader07]

quote: "The intake is the PID for Intake pressure sensor measure at kPa but i can switch it psi, what's the normal psi for the MAP on idle and while driving"...
I went back thru my torque setup and found that the pid used for monitoring vacuum by the MAP is called turbo boost and vacuum gage. It is a standard pid not a GM extension so you should see it the list of displayable values when adding a gage. It gives the value in/hg which as I indicated at idle should be 16-20. further, with the key off, it should provide some "relative value" for your "barometric pressure" depending on your altitude if I understand the operation. sorry I wasn't more specific... I had set this up a long while ago and thought the parameter was more specifically identified as absolute manifold air pressure.

So i've added the turbo boost and vacuum gage and i'm getting this:


I've also uploaded a video of my live data:

You've mentioned that my vacuum readings should be in the 16-20 range on idle but I'm seeing -9 to -10 both on idle and at ~2500 RPM what does that mean? it seems way off from what you mentioned.

 

[budwich]

hmmmm.... good effort, thanks for the info. I watched the video. It seems somewhat strange. First, as you have mentioned, I saw the "blips" of temperature changes.... very weird. Then as you mentioned, the vacuum gage seems like it doesn't really follow anything in terms throttle movement. Tjbaker57 and I have exchanged some conversations in and around the turbo boost / vacuum pid. He indicates that its seems to have some "magic" in behind the torque app to create the value. It maybe that that "magic" isn't working right with the app and thus you are seeing the "funny result". I know on my 2008, it has worked well. Having said that, my timing advance pid stopped working the other day... perhaps also my elm327 isn't the best (it does show errors in the status screen, and does warning me during some setups of gages.... note the obd status can be found on the main screen "pin wheel" on the right side).

Associated with the MAP, have you checked the electrical condition at the sensor connector... perhaps your wiring is marginal. IF you have access to a hand vacuum pump, as I mentioned, you can tested your MAP by connecting it to the hand vacuum pump, create a vacuum which the pump will display and then with your key ON, read the display of the gage that you show. They should agree. You can then add more vacuum and see if the display changes. This test will check that MAP response. Go from the result. On the temperature side of things, I am thinking you have a sensor wiring issue which is causing problems. Do you live some where there is a "rodent issue"... ie. wire chewing.

 

[ghost_leader07]

Thanks for your prompt response,

Associated with the MAP, have you checked the electrical condition at the sensor connector... perhaps your wiring is marginal. IF you have access to a hand vacuum pump, as I mentioned, you can tested your MAP by connecting it to the hand vacuum pump, create a vacuum which the pump will display and then with your key ON, read the display of the gage that you show. They should agree. You can then add more vacuum and see if the display changes. This test will check that MAP response. Go from the result.

I don't have access to a vacuum pump at the moment but I'll try to find one, i still have my original MAP sensor maybe i could hook it back and check my vacuum readings again?

On the temperature side of things, I am thinking you have a sensor wiring issue which is causing problems. Do you live some where there is a "rodent issue"... ie. wire chewing

I don't think it's a wiring issue on my truck because I've hooked my elm327 to another vehicle (2016 Dodge) and saw the same temp drop it's unlikely that a wiring issue would cause the same temp "blips" on two different vehicles it's probably a glitch in the app or elm device. Having said that I'll take a look around my ETC sensor connection and wiring around my truck again, there is no complaints in my area about any rodent activity as far as I'm aware.

I'll do the tests you recommended and keep you posted.

 

[budwich]

ok... your test on another vehicle helps rule out some of my suggestion on the temp readings. The other place to look is the elm327 settings as there are thing like speed and such that may not be set appropriately for your particular elm327. They should be checked... obd status tab in the app... same place where you find the error status.

 

[ghost_leader07]

UPDATE:

Sorry I haven't posted an update in a while i got a bit busy and I was doing more testing and some modifications but here's the latest updates regarding my p0171 code:

Thanks to @budwich suggestion about the MAP sensor I've replaced the one that i installed recently and put back the original one after about 25 miles of driving my p0171 error disappeared and my idle went back to normal idling around 600rpm instead of high 900rpm and hasn't appeared again, now that I've put around 50 miles everything seems normal so far,

also my FT both long and short are within -4% & +4%, I did a modification to my exhaust by deleting the cat (straight pipe) which lead to a notable increase in acceleration and I've replaced the air filter which wasn't very dirty just for good measures.

here's a short clip of the live data via torque app:

Ignore O2 downstream sensor readings due the cat delete.

I'll keep monitoring the data and continue driving to see if anything changes but so far so good.

 

[mrrsm]

Okay... But....

New York Emissions Testing & Smog Check - 2025 Locations

Are you looking for the latest emissions testing requirements in New York? This guide has all of the regulations and testing locations for you to get your car tested. Click to find the location near you. Find addresses, hours of operation and phone numbers of testing stations near you.

www.emissions.org

 

[ghost_leader07]

Okay... But....

New York Emissions Testing & Smog Check - 2025 Locations

Are you looking for the latest emissions testing requirements in New York? This guide has all of the regulations and testing locations for you to get your car tested. Click to find the location near you. Find addresses, hours of operation and phone numbers of testing stations near you.

www.emissions.org

Well like I've mentioned in my OP I'm not from the USA and i don't have any emission regulations in my country plus I'm only using this mod as a temporary thing I'll be installing a catalytic converter soon...

 

[mrrsm]

Your Profile indicates that you live in New York City, New York.

 

[ghost_leader07]

Your Profile indicates that you live in New York City, New York.

Yeah sorry about that I've used my friend's address when i signed my account.

 

[Mooseman]

Please edit your profile to show your correct location. We have many international members with proper locations showing. All are welcome here!

 

[ghost_leader07]

FOLLOW-UP:

After about an hour drive in a traffic on a hot day my P0171 code came back accompanied with high ~900 RPM on idle, I've recorded some live data and screenshots right away.



The P0171 was triggered (pending code) when the truck was idling i turned off the A/C and as soon as i turned it back on my rpm jumped to ~900 it could be a coincidence i was monitoring the live data the whole time on my phone and saw an increase in short fuel trims for brief moments (around +7% and my long fuel trims were around +2.34%) before the code is triggered then i took it on a 15 min drive and recorded this:

Short clips of STFT & LTFT graph:

What i did so far:
-Replaced MAP sensor (I've used brand new genuine Delphi part).
-I did a vacuum leak test from both sides (air filter and brake booster) and found 0 leaks but I'll be doing another test just to be 100% sure.
-Replaced Fuel pressure regulator.
-Replaced fuel filter.
-Checked my fuel pressure (it was around 48-49psi both key on and on idle).
-Cleaned and tested the fuel injectors.
-Replaced intake manifold and throttle body gaskets and torqued it to spec.
-Replaced ECT sensor (with ACDelco).
-Replaced Upstream O2 sensor (with ACDelco).
-Replaced air filter.
-CAT delete.
-Checked exhaust manifold for cracks and nothing is showing ( i'll check again to just to be 100% sure).

What am i missing? could it be a bad ECU or a throttle body?

Can anyone point me towards the right direction?

Any suggestions are greatly appreciated.

 

[mrrsm]

Yes… A Failing Fuel Pump can also trigger a P0171 Code.

So you might consider examining the behavior of the Fuel Pump in a Non-Invasive manner using either a PICO-Scope Model #2204A (or LATER Model) or a Hantek Model# 1008C along with using a Hantek Model# CC-65 Low Amperage Clamp.

What Equipment is Necessary for this type of Testing?

(1) A Laptop Computer.

(2) An Inexpensive Oscilloscope that should come with its own unique Scope Analysis Software.

(3) A Low Amperage Clamp set to around 20 Amps.

(4) A Hantek 20:1 Voltage Attenuator.

(5) A Fuse-able Link Loop with a 15 Amp Fuse installed. It MUST have Small Blades on the wire ends to plug into the Fuel Pump Relay Fuse Location and NOT Damage the Fuse Block insert points.

What am I supposed to be LOOKING for during this Test?

Watch THIS Video and follow along with the VOP (Video Original Poster) as he explains the simple set up and use procedures...just use the Fuel Pump Fuse on the GMT360 instead of a Fuel Pump Relay insert points as the VOP describes. The Principles will be the same whenever using a Low Amperage Clamp:

If your Fuel Pump is presently performing nominally, the “Voltage Over Time” Graph on your Laptop Screen should show a Good Wave Form as shown in this image:



That Jagged Horizontal Line is displaying the amount of the Amperage Draw on the Left Vertical Margin Scale and the Time Segment Scale on the Horizontal Axis. Those ‘Jagged Ups & Downs’ represent the individual Copper Commutator Segments inside of this Known Good Fuel Pump as they actuate under the influence of the 12 Volts DC running the Electric Pump and drawing in the necessary steady Amperage to function properly.

If YOU can see ANY Breaks or Gaps in that Jagged Horizontal Line that should appear as uniform as the example image, this would indicate a Damaged or Failing Fuel Pump and replacing the pump would be in order. Please understand that as long as your Oscilloscope Leads and Fuel Pump Fused Link Loop are good… then THIS Test is DEFINITIVE and will not involve any Guess Work.

Anyone can prepare for using this Equipment and Procedures by visiting the PICO-Scope Site and Downloading and Installing their FREE Software for your particular Laptop Computer Operating System. This nice feature here is that you can actually Practice Using the PICO Software ...without having to purchase any equipment first and determine if these types of procedures will help you, without having to just R&R the Fuel Pump without knowing whether it is actually having any subtle ...or major issues.

https://www.picotech.com/downloads

Amazon carries a wide range of Automotive Oscilloscopes and Suppot Equipment required to use them that range from just a few Hundred to Thousands of Dollars. THESE are the better Introductory Choices:

Hantek Model #1008C Kit (Eight Channels + Signal Generator):

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

www.amazon.com

PICO-Scope Various Model Oscilloscopes (Two Channels:

Amazon.com : picoscope 2204a

Hantek Model #CC65 Low Amp Clamp:

Amazon.com

Hantek 20:01 Voltage Attenuator: (NOT needed with the Low Amperage Clamp for THIS Test)

Amazon.com

 

[ghost_leader07]

Yes… A Failing Fuel Pump can also trigger a P0171 Code.

So you might consider examining the behavior of the Fuel Pump in a Non-Invasive manner using either a PICO-Scope Model #2204A (or LATER Model) or a Hantek Model# 1008C along with using a Hantek Model# CC-65 Low Amperage Clamp.

What Equipment is Necessary for this type of Testing?

(1) A Laptop Computer.

(2) An Inexpensive Oscilloscope that should come with its own unique Scope Analysis Software.

(3) A Low Amperage Clamp set to around 20 Amps.

(4) A Hantek 20:1 Voltage Attenuator.

(3) A Fuse-able Link Loop with a 15 Amp Fuse installed. It MUST have Small Blades on the wire ends to plug into the Fuel Pump Relay Fuse Location and NOT Damage the Fuse Block insert points.

What am I supposed to be LOOKING for during this Test?

Watch THIS Video and follow along with the VOP (Video Original Poster) as he explains the simple set up and use procedures...just use the Fuel Pump Fuse on the GMT360 instead of a Fuel Pump Relay insert point as the VOP describes. The Principles will be the same whenever using a Low Amperage Clamp:

If your Fuel Pump is presently performing nominally, the “Voltage Over Time” Graph on your Laptop Screen should show a Good Wave Form as shown in this image:

View attachment 101969

That Jagged Horizontal Line is displaying the amount of the Amperage Draw on the Left Vertical Margin Scale and the Time Segment Scale on the Horizontal Axis. Those ‘Jagged Ups & Downs’ represent the individual Copper Commutator Segments inside of this Known Good Fuel Pump as they actuates under the influence of the 12 Volts DC running the Electric Pump and drawing in the necessary steady Amperage to function properly.

If YOU can see ANY Breaks or Gaps in that Jagged Horizontal Line that should appear as uniform as the example image, this would indicate a Damaged or Failing Fuel Pump and replacing the pump would be in order. Please understand that as long as your Oscilloscope Leads and Fuel Pump Fused Link Loop are good… then THIS Test is DEFINITIVE and will not involve any Guess Work.

Anyone can prepare for using this Equipment and Procedures by visiting the PICO-Scope Site and Downloading and Installing their FREE Software for your particular Laptop Computer Operating System. This nice feature here is that you can actually Practice Using the PICO Software ...without having to purchase any equipment first and determine if these types of procedures will help you, without having to just R&R the Fuel Pump without knowing whether it is actually having any subtle ...or major issues.

https://www.picotech.com/downloads

Amazon carries a wide range of Automotive Oscilloscopes and Suppot Equipment required to use them that range from just a few Hundred to Thousands of Dollars. THESE are the better Introductory Choices:

Hantek Model #1008C Kit (Eight Channels + Signal Generator):

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

Hantek 1008C 8CH Automotive Diagnostic Oscilloscope: Amazon.com: Industrial & Scientific

www.amazon.com

PICO-Scope Various Model Oscilloscopes (Two Channels:

Amazon.com : picoscope 2204a

Hantek Model #CC65 Low Amp Clamp:

Amazon.com

Hantek 20:01 Voltage Attenuator: (NOT needed with the Low Amperage Clamp for THIS Test)

Amazon.com

Thank you for responding,

what made you think that i might have a failing fuel pump? can you please elaborate? my truck starts right up and it doesn't stall.

Thank you again.

 

[mrrsm]

This Instructor will provide THE BEST Answer imaginable:

 

[ghost_leader07]

This Instructor will provide THE BEST Answer imaginable:

Thank you again for your prompt response,

However you didn't answer my question why do you believe that my fuel pump might be failing? is there's something in the data I've provided that indicates an issue with the fuel system? what about my fuel pressure? 49psi is it normal or low? please elaborate.

Sorry for the many questions I'm not a mechanic and i would to try something a bit basic to determine if my P0171 code is caused by a fuel problem such as a weak/failing fuel pump.

Much appreciation for your time.

 

[mrrsm]

The reasons for suspecting the Fuel Pump are manifold:

(1) Having R&Rd most of the components in the A/F system that are ordinarily involved with persistent LEAN CODE events, you've exhausted the majority of the actions ordinarily pursued with trying to solve this unusual problem.

(2) The P0171 Code is one that if thrown in absence of other LEAN CODES; IE, P0300-P0306 ...can present with such subtlety as to become indeterminate by any definite cause.

(3) In the absence of performing a study of the ACTUAL Fuel Pump Amperage Draw with the engine not only Idling, but also observing this condition with the RPM raised well above an Idle... you might never actually SEE what the Pump Failure looks like unless pushed to these levels.

(4) Performing an Oscilloscope Analysis is not the ONLY way to accurately determine the STRENGTH (or lack of it) inside of the Fuel Pump... It is just The BEST way to do so.

(5) Doing this Procedure will easily and painlessly reveal the ACTUAL Amperage Draw the Fuel Pump experiences under Stress and proclaim its Operational RPM for comparison of these parameters against what is considered to be Normal.

(6) Once you have this Equipment in your hands and have used it to your satisfaction, it will open up all of the other doors to you for Better Automotive Diagnostics from then on.

 

[ghost_leader07]

The reasons for suspecting the Fuel Pump are manifold:

(1) Having R&Rd most of the components in the A/F system that are ordinarily involved with persistent LEAN CODE events, you've exhausted the majority of the actions ordinarily pursued with trying to solve this unusual problem.

(2) The P0171 Code is one that if thrown in absence of other LEAN CODES; IE, P0300-P0306 ...can present with such subtlety as to become indeterminate by any definite cause.

(3) In the absence of performing a study of the ACTUAL Fuel Pump Amperage Draw with the engine not only Idling, but also observing this condition with the RPM raised well above an Idle... you might never actually SEE what the Pump Failure looks like unless pushed to these levels.

(4) Performing an Oscilloscope Analysis is not the ONLY way to accurately determine the STRENGTH (or lack of it) inside of the Fuel Pump... It is just The BEST way to do so.

(5) Doing this Procedure will easily and painlessly reveal the ACTUAL Amperage Draw the Fuel Pump experiences under Stress and proclaim its Operational RPM for comparison of these parameters against what is considered to be Normal.

(6) Once you have this Equipment in your hands and have used it to your satisfaction, it will open up all of the other doors to you for Better Automotive Diagnostics from then on.

Thank you for the comprehensive response,

Doing an analysis as you've suggested requires the tools (a bit expensive for my budget) and the knowledge which are both above my capability, I'm just a DIY guy who's looking for some basic diagnostic steps to fix my issue, so if there's a simpler way to determine if my fuel pump is at fault here is greatly appreciate it,

I read online that the normal fuel pressure for my truck (2004 Trailblazer 4.2 i6) should be between 50-57psi but mine reads around 48psi should this be an indication for a weak fuel pump? I've replaced FPR and cleaned the fuel injectors and measured the resistance between all injectors and they were around the same ohms, i couldn't test the fuel injectors for leaks because i don't have the equipment for it, however i did a leak down test there wasn't any big drops in fuel pressure.

what should i do to get my fuel pressure from 48psi to 50-57psi spec range?

Thank you for your time. I appreciate it.

 

[azswiss]

Since you have already R&R'd the FPR & fuel filter you could also do a visual check for crimps in the fuel line.

 

[budwich]

did you look at the freeze frame data when the code was set?

 

[mrrsm]

In previous Postings... @azswiss and @budwich both raised the issue about what if any "Misfire Counts" were evident and you vaguely mentioned "32,000" during a particular Scan when your ODB2 Scanner was acting up.

With that reply in mind, are ALL of your Spark Plugs Identical? In the absence of making a very close inspection, a mispackaged or 'Customer Return' errant Spark Plug that is either of "colder" design or different from the other (5) in some other way (perhaps improperly gapped?) might get accidentally installed and if so, this could make all the difference here.

Also... Please consider that even with your extra efforts at "Cleaning the EFIs and Replacing their 'O' Rings..." the actual functionality of the EFIs remains hidden from plain view and can only be discovered by observing them working in a running engine and viewed 'in action' on an Oscilloscope-Laptop Screen.

I know, I know,... it's academic to suggest the notion at this stage of trying to solve this problem...

Nevertheless, please be aware that if one or more of your EFIs have "Sticky Pintle Valves" they will easily reveal themselves on a Scope according to the Example shown in the image below. A Poorly Functioning EFI will NOT have the 'tiny hump' I've highlighted inside the Red Circle of this Good, Known EFI Wave Form Image:



THAT tiny artifact is very good to see, because it indicates the exact point at which the EFI Pintle Valve CLOSES, and so its absence from the images on screen will prove if any of the EFIs are Sticking OPEN and therefore NOT allowing any Fuel to Atomize and Spray into the Combustion Chamber. Ergo? A Temporary LEAN A/F Condition could occur in such a case as this.

 

[ghost_leader07]

did you look at the freeze frame data when the code was set?

I didn't find any freeze frame data stored i guess since it's not a confirmed fault yet it won't show (still in pending) i didn't clear any of the codes since the first pending p0171 code, it did disappear after switching the MAP sensors for a while then came back on, i noticed that the code triggers at idle or low speeds it never came on when the vehicle is under load.

I was idling in my driveway while messing with A/C when it was triggered as i mentioned the code is usually triggered on idle or at low speeds i don't know what that means but it has been consistent.

Another thing I'd like to confirm with you is my fuel pressure it's currently at 48psi. i read in the service manual should be between 50-57psi.

Let's say there's a -/+2 difference due the fuel gauge tester quality or lack of, my fuel pressure could be either -/+48 psi.
could this indicate a problem with the fuel delivery system? Since I've replaced FPR and cleaned the fuel injectors what else could potentially cause my fuel pressure to be "slightly" below specs? Weak/faulty fuel pump? Leaky injectors? I've checked the wiring to the fuel injectors and it seems good also I've monitored the injectors pulse width on idle and they seem to be within range.

@MRRSM suggestion to use a Oscilloscope would be the right way to determine the condition of my EFI system but as i mentioned before I'm not mechanically inclined also we don't have these kind of equipments in my country (I'd have to order them and it'll take months to arrive)

I believe i don't have air delivery issue since i pretty much checked and replace most of the parts in that system. However I'll do another smoke test and exhaust manifold check so i can rule out the air side of the issue and focus on the fuel delivery.

I've replaced my o2 sensor a while ago trying to fix the p0171 code, could it be damaged after running lean for a while?

My apologies for the lengthy reply.

 

[ghost_leader07]

In previous Postings... @azswiss and @budwich both raised the issue about what if any "Misfire Counts" were evident and you vaguely mentioned "32,000" during a particular Scan when your ODB2 Scanner was acting up.

My obd2 scanner is pretty cheap and it's not 100% reliable but I'm try to get some basic data until i get a better one, my truck doesn't appear to have any misfires i mean when cruising at high speeds it runs smooth and performs "fine" 32,000 could be a glitch due the scanner's delay.

With that reply in mind, are ALL of your Spark Plugs Identical? In the absence of making a very close inspection, a mispackaged or 'Customer Return' errant Spark Plug that is either of "colder" design or different from the other (5)

Yes. I've replaced them a while ago and they were identical.

some other way (perhaps improperly gapped?) might get accidentally installed and if so, this could make all the difference here.

I believe my spark plugs were pre gapped .043 from the factory

Also... Please consider that even with your extra efforts at "Cleaning the EFIs and Replacing their 'O' Rings..." the actual functionality of the EFIs remains hidden from plain view and can only be discovered by observing them working in a running engine and viewed 'in action' on an Oscilloscope-Laptop Screen.

I understand that using an Oscilloscope would reveal much accurate readings but i don't have access to one and ordering one would take months to arrive plus i don't have the skills to read it correctly, However I've measured the ohm resistance on all of them and got a consistent reading of 12.6 across all and monitored injectors pulse width briefly on idle and got around 3ms on all as well.

 

[Mooseman]

Not sure if you have a MAF (RockAuto does list one), have you tried cleaning or replacing it? I was looking over the basic code definition and it lists this as one of the possible causes.

A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor


Read more at: https://www.obd-codes.com/p0171
Copyright OBD-Codes.com

One thing that could cause this is the vent hose between the valve cover and intake resonator. It's easy to miss if it's not on right. Not sure if you already did this but checking for vacuum leaks using carb cleaner is also a good method of finding vacuum leaks.

 

[ghost_leader07]

Not sure if you have a MAF (RockAuto does list one), have you tried cleaning or replacing it? I was looking over the basic code definition and it lists this as one of the possible causes.

I don't have a MAF sensor on my truck. I do however have an IAT sensor.

One thing that could cause this is the vent hose between the valve cover and intake resonator. It's easy to miss if it's not on right. Not sure if you already did this but checking for vacuum leaks using carb cleaner is also a good method of finding vacuum leaks.

I did a vacuum leak test before but I'll be doing another test just to rule out vacuum leaks for good.

 

[ghost_leader07]

Hey Guys sorry i haven't updated in awhile, I've been busy and I've also been doing more testing about my issue.

I think i found something and i need your guidance, My P0171 code didn't go away after all the work i did mentioned in the OP but here's a recap:

-Vacuum leak checked with DIY smoke machine (air system was pressurized no leaks were found)
-Fuel pressure checked (around 49psi)
-Replaced intake manifold gaskets
-Replaced fuel filter
-Replaced fuel pressure regulator
-Replaced O2 upstream sensor
-Replaced air filter
-Replaced MAP sensor
-CAT deleted
-SAIS deleted

Now to my latest discovery, I've checked my exhaust manifold while chasing the damned P0171 code awhile ago and upon visual inspection I didn't see any obvious cracks however I couldn't check behind the exhaust manifold without removing it so my question is will a crack on the manifold cause my issue??

I'm saying this because while my P0171 is triggered (High idle @900rpm) and I can hear a hissing noise coming from the area between the exhaust manifold and my steering pump I couldn't exactly pinpoint where due the fan blowing at my face but it's quite audible, I can't hear it at normal idle.

another questions I'd have to ask could it be just the steering pump making that noise? if so why I can't hear the same noise at normal idle? it's definitely a hissing noise coming either the exhaust manifold or steering pump.

I'm really frustrated and I would greatly appreciate all the help I can get.
Thank you in advance.

 

[Mooseman]

will a crack on the manifold cause my issue??

Oh yes it could do that. In between exhaust pulses, air could get sucked in.

I didn't see if you cleaned your throttle body. Although you're not having idle issues, it's worth a shot. Don't forget to disconnect the battery for 30 minutes.

Does your truck have a MAF? Clean it and recheck for any vacuum leaks between it and the throttle.

When you did the smoke test, did you check all the way back to the tank? There could be a vacuum leak in the lines leading back there.

This is a point where you should do an injector balance test to check for a defective or blocked injector. You need an advanced scanner to be able to do this.

 

[ghost_leader07]

Thanks for your respond @Mooseman

I didn't see if you cleaned your throttle body. Although you're not having idle issues, it's worth a shot.

I forgot to mentioned that, Yes i did clean the throttle body.

Does your truck have a MAF?

No it doesn't, it has however IAT sensor which i haven't replaced. Can it cause a problem if it's faulty?

When you did the smoke test, did you check all the way back to the tank? There could be a vacuum leak in the lines leading back there.

all the way back to tank? i didn't know about any vacuums lines at the back what should i look for?

I did however removed the air pump and SAIS hoses and blocked it out.

This is a point where you should do an injector balance test to check for a defective or blocked injector.

I've forgot that i did clean my fuel injectors with carb cleaner when i replaced the intake manifold gaskets I've also did a basic resistance test on all of the injectors and all of them were identical.

Other thing i noticed at a cold start up that my exhaust and engine is making some hiccup/popping noise while idling, those hiccups were so strong i feel them all over the truck.

Any ideas about the hissing noise I've mentioned btw? does it sound like an exhaust manifold leak to you?

 

[Mooseman]

No it doesn't, it has however IAT sensor which i haven't replaced. Can it cause a problem if it's faulty?

Not really. Since you don't have a MAF, if it did leak, you'd just have some unfiltered air getting in.

What are the fuel trims like? I know you put in a new O2 sensor so trims should be checked. Check while idling, revving and driving.

There's no vacuum lines around there. Maybe the power steering pump but you could eliminate that by taking the belt off and listening again. It certainly could be the manifold. Check the bolts as they have a tendency of popping their heads over time.

 

[ghost_leader07]

What are the fuel trims like? I know you put in a new O2 sensor so trims should be checked. Check while idling, revving and driving.

I'm having issue with live data on my cheap obd2 scanner i'm getting about 6% on LTFT but it keeps disconnecting as soon as i turn my engine on I'm planning on getting a good quality scanner soon but in the meantime i'll check my fuel trims at a local shop.

There's no vacuum lines around there. Maybe the power steering pump but you could eliminate that by taking the belt off and listening again. It certainly could be the manifold. Check the bolts as they have a tendency of popping their heads over time.

I think it's a good idea i'll try it and check bolts as well, i'll keep you posted.

 

[Mooseman]

Check with @TJBaker57 . He knows the OBD adapters. I know those little blue ones, like the VeePeak work well.