yes another P0171 and 900 RPM thread that needs your help

[gica]

Hello to all,
I have a 2004 Trailblazer that I just finished rebuilding the head with valve job. The reason I took out the head was the exhaust manifold cracked and was making a loud sound so in trying to remove one bolt broke and I could not get it out for the life of me.
I had no codes from the leak, RPM was fine. I cleaned the throttle body, replaced gaskets etc. Put it all back and voila RPM goes to 900 for awhile then on his own back to 650.
If I clear the codes and the PCM memory the RPM stays at 650 for a while and then when the RPM goes to 900 the P0171 pops up. I recorded PIDs and the STFT is up and down at idle it stays plus or minus 5 when I press the gas to take off it sometimes jumps to +17 to -10 then back and forth at 0 and at that range. Only goes thtat high when under load not cruising.
The LTFT also goes up on take off it went as high as 19 then it immediately stabilizes to +9 sometimes goes to 0 then 3 then back to 9. When I stop and idle it goes to 1.6 if idle is 650 or 2.6 if idle is 900. But it goes like that up and down all the time not slowly. The Bank one sensor 1 O2 sensor is going from 0.1 to 0.9 all the time, back and forth.
Bank one sensor 2 it sometimes stays at 0.8 to 0.7 and then it sometimes drops to 0.2 and 0.3 and back up. It's not supposed to do that is it? temps stay at 197 when driving and 201 when idle. When going up the hill it went to 206.
Car drives fine. MAF goes to 40 something g/s on takeoff and down to 4 at idle. I have not changed these yet. Don't remember how old the O2s are, but not too old.
New radiator and Temp Sensor is new also thermostat is new, radiator new, fan new all AC Delco
The Mass Airflow sensor is not new.
I bought a smoke machine and did the test and I had smoke come out from the 2 hoses that go to the SAIS. I did not install a plate yet to check if that could be the problem.
I did try to find a leak using a carb cleaner spray but did not notice anything.
The intake bolts are torqued to 89in/lb.
I am currently working on my son's 328i BMW and doing valve job and changing the head because of a stupid ass code caused by Vanos pressure being lost due to dumb German engineering and not knowing about it before doing a head swap 6 month ago. That head had the damage that causes the code, and it can only be fixed with a new head.
I need some opinions on the Chevy. I always ask for help when I am stuck. I read it all and watched most YouTube videos on this issue.
I do have a bidirectional Autel 708 scanner.
Thanks in advance for any help guys. Hope someone is still around driving these.

 

[TollKeeper]

The commanded throttle position is a bit concerning to me, but I have to admit, my knowledge of the 4.2 is limited.

 

[Mooseman]

I bought a smoke machine and did the test and I had smoke come out from the 2 hoses that go to the SAIS. I did not install a plate yet to check if that could be the problem.

Yes, block that off as that could give a false lean condition as air is introduced into the exhaust. It's a useless system. Have the codes for it deleted via a tune. I deleted mine even before it failed.

Don't even bother looking at O2 sensor 2. All it does is report cat efficiency. Does nothing else.

MAP sensor might be off too. It can get gummed up. Clean or replace it.

If that doesn't resolve it, do a vacuum leak check using carb cleaner, especially around the intake manifold.

 

[gica]

Yeah I did the carb cleaner test and nothing. I will have to block the SAIS off just to make sure. this code sucks and the 900 RPM also. I previously read about the second O2 sensor not having much of a bearing on this.

 

[budwich]

Yes, block that off as that could give a false lean condition as air is introduced into the exhaust. It's a useless system. Have the codes for it deleted via a tune. I deleted mine even before it failed.

Don't even bother looking at O2 sensor 2. All it does is report cat efficiency. Does nothing else.

MAP sensor might be off too. It can get gummed up. Clean or replace it.

If that doesn't resolve it, do a vacuum leak check using carb cleaner, especially around the intake manifold.

I think that this thread was posted in the wrong sub forum.... hopefully it will get moved.

Anyway, the freeze frame data seems somewhat "funny" as the fuel trims don't appear to be outside the range ... or in the range to set the code.... maybe that is an issue with the reporting system.

Your "visual story" indicating seeing values up in the high teens is more like it. Basically the "average sum" of the trims "above" +/- 25 causes the code.... that is likely based on your description.

As suggested, you could temporarily block the sais port on the block with a plate of some sort. Go from the result. The other area of "potential" is the MAP. One check is to have key on / engine off and read the map with your data reader. Compare the result, with your elevation. It should show the pressure is kpa that it is currently seeing. It should be "reasonable" for the elevation but also there might be a bit a "slop" for weather (ie. extreme high or low pressure in the area).

added... I don't know what's up with the forum / browser.

 

[gica]

Ok, good news so, I replaced the SAIS and the RPM is not going up to 900. At least yesterday and today it hasn't. I have not seen the P0171 code yet. The LTFT is swinging still saw it at +15 but for a second, now at idle when warm it goes to -1.6 or -2.3. The STFT swings to -19 at idle. other than that they both are within ranges. The high or low swings are at idle for the short and under load for the long really briefly it mostly stays at +6 otherwise and goes to 0 sometimes. That secondary switch for the pump was probably getting stuck from being aged. Any thoughts? Should I still change the sensor on the intake, MAP or the upstream O2? Or leave them alone? I have not reset the PCM or any of the values that were prerecorded.

 

[gica]

Shit never mind it went to 900RPM again and Pending P0171

 

[Mooseman]

How's the exhaust manifold? Any cracks?

 

[gica]

How's the exhaust manifold? Any cracks?

The reason I am here was that the exhaust manifold cracked, broke a bolt trying to change it and I had to take the head off. I must say I drove it like that with the manifold cracked for a month and had no codes. RPM was fine. But it has a new manifold now, valve job etc. New timing chain and guides all new valve seals. Trims oscilate too much. Before I replaced the Air injection part the idle LTFT was at 3.1 now when warm it stays at -2.3 at idle. But the STFT goes from -19 to +15 not all the time but for brief seconds. I have not changed the O2s yet or MAP.

 

[budwich]

I had similar experience with a crack exhaust manifold.... no codes. One GM tech. was suggesting there should be codes BUT others say, "it depends". Anyway, the swings in the stft are somewhat "unusual".... especially if they are actually "waggling" like that in a short time period (less than seconds). IF you are making that statement as the "range over a long time period" then it is not as "disturbing" but still an issue as it is likely the cause of the coding. In terms of ease of effort, I would check / change the MAP first (wiring and seating / seal) and then check and change upstream o2 next... looking at wiring and the sensor visually (contamination)

 

[gica]

OK I was going to order them. The downstream doesn't matter right?
I have to go fix the damn HVAC actuator I accidentally reset it yesterday and now it started to click again. All that needs to be done is remove and set it with the flap. I don't know if it is actually broken but when reset it does a 180 or 360 and goes on an endless loop. Anyways easy fix
yesterday I reset the trims and everything that could be reset and today until about 10 minutes ago I thought maybe it's fixed and right then it went to 900 RPM P0171 and all. Nice the car is reading my mind now hahaha.

 

[Mooseman]

The downstream doesn't matter right?

That is correct.

 

[gica]

So I changed the upstream O2 and the MAP and for 5 days I thought it was over, but the 6th day it was back to the PO171. The difference is it takes longer to get to it. Car runs great but I still get some high STFT and LTFT. For instance it will go to 12 or 14 for a split second on both when I come off the load on the accelerator. Split second, with load it goes to 7 or below on the LTFT and +- 5 on the other one. At idle it stays at -3 or +2 and change. So what next?

 

[Mooseman]

Have you blocked off the SAIS yet? I know you replaced the valve but the system may still be defective.

Either there is too much air or not enough fuel, or the O2 sensor thinks that it's lean. For too much air, you said you checked for vacuum leaks. For not enough fuel, did you check fuel pressure? It would make sense if under load, when there is more fuel demand, it runs out of fuel if the pump isn't keeping up with demand. Could also be the fuel pressure regulator if it's bleeding off pressure too much.

 

[mrrsm]

Yes....

And for any other interested Members (and Lurkers) This is a Very Simple (EZ-PZ) R&R...

Remove the air cleaner outlet duct.



Disconnect the electrical connector from the secondary air injection (AIR) reaction solenoid valve.

Disconnect the AIR pump air outlet pipe from the AIR solenoid valve.




Remove the nut (1) securing the Transmission Fluid Level Indicator Tube (2) to the AIR Solenoid Valve.

Remove the Transmission Fluid Level Indicator Tube (2) from the AIR Solenoid Valve Stud (3).

Remove the 2 AIR Solenoid Valve Studs (3).

Remove the AIR Solenoid Valve (4) and the Gasket (5) from the Engine.

NOTE:

Examine the Two Bolt SAIS Solenoid Gray Graphite Impregnated Solenoid Mount Gasket (#5 - Red Hash Lines Hi-Light) for ANY signs of EROSION that will allow Ambient Air to Pass into the Exhaust Stream and confuse the Upstream O2 Sensor and replace it if necessary.



Source:

https://www.justanswer.com/chevy/20pgq-chevy-trailblazer-2005-code-0410.html

 

[Mooseman]

Another thing you can try is to clean the MAF and MAP sensors.

 

[budwich]

Another thing you can try is to clean the MAF and MAP sensors.

I don't think 2004's have a MAF... he changed out the MAP already. :-(

check to make sure that the MAP seating is good and not leaking. It is possible that the MAP is "less than good" as I had issues with a replacement or two.

Positive LTFT likely points to air leaks.... As mooseman asked, block off the sais port to ensure that system is not the issue STILL.

 

[Mooseman]

Car drives fine. MAF goes to 40 something g/s on takeoff and down to 4 at idle. I have not changed these yet.

He did mention a MAF. May be a calculated value.

 

[gica]

This is was I meant to post

VID-20230309-WA0001.mp4

Shared with Dropbox

www.dropbox.com

 

[gica]

So the issue is ongoing even after changing the upstream O2 sensor and MAP. But now it hapenns after 5 days, so some improvement. I am waiting for a fuel pressure kit from Amazon to test the pressure at idle, with engine off and at some RPM. Wanna rule that out. Other than that the injectors? I mean the car runs great. I don't know what the next step would be.

 

[Mooseman]

Cleaned up unrelated posts.

 

[mrrsm]

I congratulate you for owning and using your Autel DS-708 MaxiDas Scan Tool.

These images are of a Brand New OEM GM ACDelco Small Rubber EGR Elbow Hose located in between the Lower Air Plenum Chamber and the Forward Spigot on the Valve Cover.

Over time, the snugness of the two hose connections in between might have become loose enough over time to allow un-metered Ambient Air to get pulled into the Intake Stream. Even though this might be a very slim contribution or Air, at this point in your investigation, Leaving No Stone Un-Turned might pay off with the replacement of this "Thing":



Even though you've already tightened down the staggered Intake Manifold Trapped Fasteners to the correct mild Torque of only 89 Inch Pounds, the Black Plastic Runners and IM Flanges are NOT supposed to ever make direct contact with the metal surfaces around the Intake Ports in the Aluminum Engine Head.

Rather, the Original "Plump" shape of the OEM Gaskets gets ruined enough, such that the uninformed might make the mistake of applying a "Bolt Breaking" tightening down force and possbly risk snapping off some of the Fasteners. Of course, this would allow Ambient Air to get vacuumed into the Cylinders on the Intake Strokes and FUBAR any possibility of getting the Stoichiometric Fuel/Air Perfection the PCM strives to achieve. The Clue here is that the Trapped Fasteners will spin freely in place inside of and around the IM Flange perimeter.

What happens is that after over 20+ Years of suffering with Changes in Engine and Air Temperature, plus the Vibration and Pendulum action of the Engine Rocking the IM Back & Forth in between the Weight of the Heavy Throttle Body mounted on one side of the IM, counter-balanced by the Weight of the Heavy PCM mounted on the other side, the Three Figure 8 Gaskets get Squeezed and Flattened down to the point where they will no longer seal.

And as we all know, the Gel-Filled Motor Mounts supporting the 4.2L Engines on MOST of what is left of the running GMT360s can fail and leak as they allow these engines to constantly "Shake like a Chihauhau Sh*tting a Peach Pit" and thus, accelerate these Three IM Gaskets to wear and squash down flatter than a Pancake. After that, the Classic P0300 (P0301 - P0306) "Mystery Misfire Syndrome" can soon settle in.

 

[budwich]

So the issue is ongoing even after changing the upstream O2 sensor and MAP. But now it hapenns after 5 days, so some improvement. I am waiting for a fuel pressure kit from Amazon to test the pressure at idle, with engine off and at some RPM. Wanna rule that out. Other than that the injectors? I mean the car runs great. I don't know what the next step would be.

I don't think you still haven't indicated blocking off the sais which basically costs nothing to try.

 

[gica]

I actually completely changed it. Bought a new one.

 

[budwich]

yes we know that BUT that is not what was suggested as this is for TESTING not a permanent "fix". Just because you replaced the system does not mean things are totally good. Anyway, you made some progress.

 

[gica]

I don't have the cover to close it up but I can make a temporary one. You're right I have to try it out.

 

[gica]

I congratulate you for owning and using your Autel DS-708 MaxiDas Scan Tool.

These images are of a Brand New OEM GM ACDelco Small Rubber EGR Elbow Hose located in between the Lower Air Plenum Chamber and the Forward Spigot on the Valve Cover.

Over time, the snugness of the two hose connections in between might have become loose enough over time to allow un-metered Ambient Air to get pulled into the Intake Stream. Even though this might be a very slim contribution or Air, at this point in your investigation, Leaving No Stone Un-Turned might pay off with the replacement of this "Thing":

View attachment 107280View attachment 107281View attachment 107282View attachment 107283

Even though you've already tightened down the staggered Intake Manifold Trapped Fasteners to the correct mild Torque of only 89 Inch Pounds, the Black Plastic Runners and IM Flanges are NOT supposed to ever make direct contact with the metal surfaces around the Intake Ports in the Aluminum Engine Head.

Rather, the Original "Plump" shape of the OEM Gaskets gets ruined enough, such that the uninformed might make the mistake of applying a "Bolt Breaking" tightening down force and possbly risk snapping off some of the Fasteners. Of course, this would allow Ambient Air to get vacuumed into the Cylinders on the Intake Strokes and FUBAR any possibility of getting the Stoichiometric Fuel/Air Perfection the PCM strives to achieve. The Clue here is that the Trapped Fasteners will spin freely in place inside of and around the IM Flange perimeter.

What happens is that after over 20+ Years of suffering with Changes in Engine and Air Temperature, plus the Vibration and Pendulum action of the Engine Rocking the IM Back & Forth in between the Weight of the Heavy Throttle Body mounted on one side of the IM, counter-balanced by the Weight of the Heavy PCM mounted on the other side, the Three Figure 8 Gaskets get Squeezed and Flattened down to the point where they will no longer seal.

And as we all know, the Gel-Filled Motor Mounts supporting the 4.2L Engines on MOST of what is left of the running GMT360s can fail and leak as they allow these engines to constantly "Shake like a Chihauhau Sh*tting a Peach Pit" and thus, accelerate these Three IM Gaskets to wear and squash down flatter than a Pancake. After that, the Classic P0300 (P0301 - P0306) "Mystery Misfire Syndrome" can soon settle in.

I already replaced the hose it was brittle and part of it broke, but it did not do it previously. As for the intake 3 gaskets they are all brand new at 89 torque.

 

[mrrsm]

Agree with @budwich ... the Mechanical Innards of the Solenoid might have just enough imperfections .. even if replaced with an Off The Shelf Brand New Item ...to have difficulty with completely closing when not electrified to the "Open" Position and allow that Damned Uncontrolled Air to *Sneak By*.

Trust me...WE are All ...On YOUR Side... and hope to help with ideas worthy of your consideration. What you read here is not meant to be viewed as any personal criticism. In most cases... Competent Mechanics often Bristle at the very idea of EVER having to Ask Anyone for Help.

We Get That... But these amazing GMT360 SUVs have thrown us ALL some Very Bizarre Screw Balls from time to time ... and thus, we always enjoy receiving all the help we can get to achieve satisfying outcomes.

 

[Mooseman]

It's easy to just use some thin sheetmetal or even aluminum foil sandwiched between the valve and gasket on the head.

 

[budwich]

The "time frame" of the coding is somewhat unusual. One other thing to look at related to the MAP is the barometric pressure setting at key on. Potentially, check this each time when starting / using the vehicle (ie. using some form of data display / output) to see if the result is "appropriate" for your area. My "map experience" wasn't very good in terms of "normal operation in general.

 

[mrrsm]

In the past... more often than not... @Mooseman has coined the solution to this problem as coming from either replacing a cracked, misaligned Exhaust Manifold or its fitment made worse by having Broken Off Exhaust Manifold Bolts.

If you want to explore this... consider using your Smoke Machine at the Exhaust Pipe by pumping in 'The Stuff" *** in reverse*** through the CAT-Can and look for anything escaping around these problem areas of the Cast Iron Exhaust Manifold.

ANY open spots ahead of the Upstream O2 Sensor in this Exhaust System is an invitation for Un-Metered Atmosphere to get pulled inside by the volumetric efficiency of the Exiting Exhaust Stream ...Drawing the stuff inwards.

The reason this issue can be so intermittent is because Cast Iron Manifolds can expand and contract in odd ways in relation with the MLS Gasket and with variations of expansion (and Warp) and contraction happening at different RPM. Even having Bad Motor Mounts can exacerbate this issue as the Engine Block rolls left and right with changes in RPM and Torque.

THIS inexpensive ($12.99) Rubber Stopper Kit might work to Plug Off the Tail Pipe after Drilling out the largest one clean through & running your Smoke Machine Piping through it:

Amazon.com

.

 

[gica]

So plug the pipe at the muffler and test from there?
I did mention that the exhaust manifold is new, and the previous cracked one did not give me any codes. This is all new stuff going on. After the head rebuild.
I will fo the test and will also look into blocking the Sais. As far as the Baro value I could not get a Baro reading from apps like Torque Pro or Obd Fusion. I will try the other scanners I have. Autel bidirectional and another Autel, and a foxwell 650 I think. One has to have Baro.
Today being the 5th day RPM went to 900 and I drove away and to take my kid to school the P0171 is pending, but bybthe time I came back RPM went back down so the Check Engine never materialized yet.

 

[mrrsm]

Yes... I know it sounds counter-intuitive... but having the Smoke Machine Cranked Up to HIGH and running the Fine White Smoke Particles in through the exhaust system backwards...WILL ... reveal any discrepancies in the system.

Again...as explained...the Mysterious disappearance of the P0171 is perhaps due to the Engine Heat cycling thermal changes in the Cast Iron and dissimilar Aluminum Engine Head as well.

The Reason GM uses an MLS (Multi-Layered-Steel) Exhaust Manifold Gasket is to compensate for these ever changing variations... and reduce Customer Complaints and Repair Returns.

 

[budwich]

So plug the pipe at the muffler and test from there?
I did mention that the exhaust manifold is new, and the previous cracked one did not give me any codes. This is all new stuff going on. After the head rebuild.
I will fo the test and will also look into blocking the Sais. As far as the Baro value I could not get a Baro reading from apps like Torque Pro or Obd Fusion. I will try the other scanners I have. Autel bidirectional and another Autel, and a foxwell 650 I think. One has to have Baro.
Today being the 5th day RPM went to 900 and I drove away and to take my kid to school the P0171 is pending, but bybthe time I came back RPM went back down so the Check Engine never materialized yet.

so when you are saying "5th day".... that sound like "time" but is it only time. Are there multiple starts? truck use EACH day of the 5?

My guess here is that the MAP is not quite "functional". I am thinking that the membrane in the sensor slowly "deforms". On one of my MAP's, I tested it with a vacuum pump and torque app as per great instruction in the forum. The thing readily worked as I increased the vacuum at 5 in-hg at a time, releasing and going up again. Initially, I thought, ok it works fine BUT after about four or five "cycles", I released the vacuum and torque reading stayed at the high vacuum (about 20 in-hg) which was kind of strange. Not sure why as my setup was "less than optimum" in terms of holding vacuum (the connector tubes were "diameter size compromised" for the setup.

Anyway, unless you installed a new "built in internet connected head", it is strange that your problem is so well timed...

Related to this.... did you keep your old MAP. IF so put it back in and see if anything changes. Go from the result.

ADDED: from our good friend, tjbaker,
Barometer
PID = 22119D
Min = 1.5
Max = 15.2
Scale = x1
Units = PSI
Equation = A/255*5*2.74+1.5
Header = Auto

 

[mrrsm]

And for Testing any MAP Sensor using a DMM:

If the vehicle uses a digital MAP sensor, instead of an analog one, you can also test it using a DMM that can Measure Frequency Signals.

1. First, set your Digital Multi-Meter to about 100 or 200 hertz.
2. Unplug the vacuum hose from the sensor and plug in a Hand-Held Vacuum Pump to the Sensor's Vacuum Port.
3. Back-Probe the Signal and Ground Wires at the Sensor Electrical Connector.
4. Turn the Ignition Key to the ON position but don't start the engine.
5. Make a note of the Voltage, Duty Cycle and Frequency Readings on your Meter.
6. Now, apply about 18 in-Hg of Vacuum to the MAP Sensor, and note the Voltage, Duty Cycle and Frequency readings on your Meter.
   • Your sensor should have about the same Voltage and Duty Cycle Readings in both tests.
   • Without Vacuum applied, the Sensor should have about 160 hertz Reading.
   • WITH Vacuum applied, the Sensor should drop to about 100 hertz Reading.
   • Consult your vehicle repair manual for specifications.
   • An Oscilloscope can also be used to Test the MAP Sensor in finer, more graphical detail:

 

[budwich]

I don't think the map is a digital map... I believe it is purely analog. I am thinking there may be some "limits" on the sensor especially when pushed to the higher end. I am thinking the vacuum at idle might be relatively high which pushes the senor to its max (if that is possible... ~1v) and it doesn't always recover.... again depending on the quality of the unit.

 

[gica]

Wanted to mention the MAP is new. Does it still apply?
I am blicking the SAIS as we speak.
Then I am measuring the fuel pressure
And finally the exhaust for leaks with tye smoke machine

 

[gica]

Ok here are the result for tye tests.
First engine on.

Second just ignition on

The fuel pump is an AC Delco at the most 2 years old. Wtf

 

[gica]

Ok smoke test shows one leak at the front of the middle muffler or whatever that is. Nothing by the manifold.


So this is the middle muffler and when knocking has full sound în the beginning and more hollow în the middle. Might be
a little plughed up.

 

[budwich]

wow... that's great work... again.
the fuel pressure seems awfully low. It could cause an issue although I thought low would cause a rich run which cause negative trims.... but just my thoughts.

waiting breathlessly on your run / ft's with sais blocked.