P0171 and P0174 Codes

[Chuck L]

2008 Chevy Avalanche 5.3.   I have been getting the 171 and 174 codes for about 3 months.  I went down the list and checked all of the probable causes:  1.  Checked for vacuum leaks several times (none found)  2. Checked fuel pressure (checks good)  3.  Cleaned the MAF sensor.    I have also gotten some other random codes during this period.  P0106 and so I replaced the map sensor.  P0507 and I cleaned the throttle body and in-turn had to relearn the engine idle; the code went away for awhile but now it's back along with the 171 and 174. I have also gotten some P0300, P0303 and P0307 codes along the way but I have been getting those misfire codes ever since I owned the truck and guessing they are not related.  I should also point out that I was getting P0430 code (catalytic converter) for a long time awhile back, but it went away months ago and I haven't seen it since   Anyway...  I'm stumped and hoping someone on here has more insight and can help.  Any help would be much appreciated.  Thanks!!!

[davester]

maybe check for exhaust leaks at the head, or where the manifolds bolt to the exhaust pipes.

[CamGTP]

Sometimes finding vacuum leaks at the intake manifold to cylinder head can be tough. They may only leak when it's running. Same with injector o-rings, being that they are 12+ years old, I'd replace them because they are cheap enough to do and it lets you inspect everything else.

 

Pull the plug on those two cylinders you have misfires for. Cylinder 7 is common to have oil build up on the plug from the AFM/DoD system.

[Chuck L]

FYI: I had a collapsed AFM lifter and pulled the entire top off the motor (including heads) and replaced all the lifters.  I bought a kit that included the lifters and all the gaskets.  I thought maybe the new intake gaskets might be leaking and I checked them several times using starter fluid and propane while it was running, including vacuum hoses and potential spots for a leak.  I am pretty sure I sprayed starter fluid around the injectors too... if there was a vacuum leak at the injectors the engine should have revved up... right?  Like you said I can replace those injector o-rings pretty cheap and easy, so I may go ahead and try that.  

 

I was thinking of going ahead and replacing that MAF sensor... A guy on YouTube said he replaced his and it solved the 171/174 codes.  I am reluctant to believe it, but at this point I am getting desperate to fix it.  

 

I know what you mean about that #7 spark plug and I have had it out many times.  I replaced that driver side valve cover pan that was suppose to solve the oil usage issue due to the defective PCV system they now use (what was wrong the old PCV).  It would sometimes smoke bad when I first started it in the morning.  After I installed the new pan it quit smoking in the morning, but now I see a cloud of smoke every now and then going down the road.  

 

 

 

[Chuck L]

Senior Enthusiast - Interesting you said I should check for exhaust leaks.  The other day when I started it up I heard what I though was a loud ticking noise and wondered if I didn't have a collapsed lifter again, but it turned out to be an exhaust leak between the right exhaust manifold and the head.  I was wondering if that might also be causing the 171 and 174 codes, even though the leak is only on one side (I checked the other side for leak).  But, I replaced the gasket and retorqued the bolts and the leak is gone but I am still getting the codes.   I did not check the rest of the exhaust as I don't hear any leaks.  If you really think an exhaust leak could cause the codes perhaps I should inspect it.  

[swathdiver]

42 minutes ago, Chuck L said:

FYI: I had a collapsed AFM lifter and pulled the entire top off the motor (including heads) and replaced all the lifters.  I bought a kit that included the lifters and all the gaskets. 

Did you delete AFM or just replace both the standard and De-Ac lifters?  If the latter, you must also replace the VLOM, it is SOP, or you will be needing new lifters again.  When the solenoids start to fail, they get out of time and cause damage to the lifters.

 

You need a scan tool like the Tech-2 that can run graphs.  Graph your O2 sensors and LTFTs while spraying water from a spray bottle or propane even around the exhaust manifolds and intake gaskets, anywhere a vacuum leak might manifest itself.

 

Check your grounds and the health of your battery first.  A bad cell in a battery can be hard to detect and cause all kinds of false alarms.

 

Watch the performance of your downstream O2 sensors with regards to the cats, if they move around like the upstream sensors, it's time for new ones.  Cheap CHICOM cats often barely last a year.  I replaced mine with Magnaflow's.

 

Not related, does your motor consume too much oil?  A new driver's side valve cover came out in 2011 which repositioned the opening for the PCV "valve".

 

Oh, what motor is this?  LY5, LMG, LC9?

[davester]

7 hours ago, Chuck L said:

Senior Enthusiast - Interesting you said I should check for exhaust leaks.  The other day when I started it up I heard what I though was a loud ticking noise and wondered if I didn't have a collapsed lifter again, but it turned out to be an exhaust leak between the right exhaust manifold and the head.  I was wondering if that might also be causing the 171 and 174 codes, even though the leak is only on one side (I checked the other side for leak).  But, I replaced the gasket and retorqued the bolts and the leak is gone but I am still getting the codes.   I did not check the rest of the exhaust as I don't hear any leaks.  If you really think an exhaust leak could cause the codes perhaps I should inspect it.  

I think you should, as, at least for my engine, several bolts were broken off the exhaust manifolds, and the engine would suck air into the exhaust and the O2 sensors would read it as the engine running too lean, and just dump fuel in to try to compensate for it.  It was further exacerbated by a failing fuel pump (it could generate about 55 psi at idle, but would drop to 10-15 psi if the engine was at all sped up).

[Chuck L]

7 hours ago, swathdiver said:

Did you delete AFM or just replace both the standard and De-Ac lifters?  If the latter, you must also replace the VLOM, it is SOP, or you will be needing new lifters again.  When the solenoids start to fail, they get out of time and cause damage to the lifters.

 

You need a scan tool like the Tech-2 that can run graphs.  Graph your O2 sensors and LTFTs while spraying water from a spray bottle or propane even around the exhaust manifolds and intake gaskets, anywhere a vacuum leak might manifest itself.

 

Check your grounds and the health of your battery first.  A bad cell in a battery can be hard to detect and cause all kinds of false alarms.

 

Watch the performance of your downstream O2 sensors with regards to the cats, if they move around like the upstream sensors, it's time for new ones.  Cheap CHICOM cats often barely last a year.  I replaced mine with Magnaflow's.

 

Not related, does your motor consume too much oil?  A new driver's side valve cover came out in 2011 which repositioned the opening for the PCV "valve".

 

Oh, what motor is this?  LY5, LMG, LC9?

I did not delete the afm and just put replacement lifters.  I did replace the VLOM during the process.  

 

I don't have a high tech scanner but maybe I should invest in one, or take the truck to someone that does .. was hoping I might find an easy answer  here... but I guess that's not happening.   

 

I think my battery and ground are fine...  are you saying these could actually cause a lean code?

 

Are you saying bad cats or O2 sensor could be causing the codes?  

 

Please review my last post and I did mention that I already replaced the valve cover pan... fixed morning start up smoke... but still have a problem with smoking/ oil consumption... while driving down the road.  

 

I'm not sure which 5.3. motor I have.  How do I find out?  Is that important?

[swathdiver]

11 hours ago, Chuck L said:

I did not delete the afm and just put replacement lifters.  I did replace the VLOM during the process.  

Awesome.

11 hours ago, Chuck L said:

I don't have a high tech scanner but maybe I should invest in one

It's the most important tool one can have and quickly pays for itself.  Look up Tech-2 and VXDIAG Nano for options.  I prefer the Tech-2.  They're about $350 delivered.

11 hours ago, Chuck L said:

I think my battery and ground are fine...  are you saying these could actually cause a lean code?

A bad cell in a battery creates all kinds of false positives and headaches.  

11 hours ago, Chuck L said:

Are you saying bad cats or O2 sensor could be causing the codes?

Failing cats possibly.  You had a P0430 previously.

 

11 hours ago, Chuck L said:

I'm not sure which 5.3. motor I have.  How do I find out?  Is that important?

In your glovebox will be your RPO sheet, look for LY5 (iron block not FlexFuel), LMG (iron block FlexFuel) or LC9 (aluminum block, FlexFuel).

 

Running higher alcohol contents can expose failing parts sooner than on gasoline.  When my cats were bad, they would throw codes sooner while burning E85 than with high octane gasoline.