Engine vacuum, P0171 and P0174 codes.

[SLCHOE]

Without proper live data from your ECM (which I outlined above in earlier posts on how exactly to get that data) all I can tell you is that about 75% of the GMs with lean codes on both banks without any obvious vacuum leaks (hoses, loose intake ducting after the maf, etc) and where a MAF cleaning/replacement didn't resolve it, turned out to be leaking intake manifold gaskets. They are very common over 120K miles and will cause these codes especially where BOTH banks are lean.

 

[Toyfare]

I checked the voltage on my MAF and it didn't not change when accelerating in park. This lead me to believe that my MAF is malfunctioning (explaining bad hesitation, shuddering, and loss of fuel economy). Delphi replacement on the way!

 

[Toyfare]

Replacement arrived and was installed with ease. Truck idles smoother (no more shuddering) and the fuel economy is greatly improved, along with engine power. I also notice that my shifts from 1-2 are a lot smoother. YMMV

 

[H0E2]

Sorry Guy's

I have been super busy since my last post anyway here is an update...

Replaced Intake Manifold Gaskets and cleaned everything up while i was in there as well...

Put everything back together no service engine soon light no shudder no hesitation nothing seems to be fixed. A quick shout out to everyone who replied i really appreciate it!!

 

[SLCHOE]

A couple of days later, the monitors should have ran. Any Check engine light?

If not, congrats!

 

[Red Rider]

I just had the p0171/4 codes come up on my 2004 Tahoe z71. They came up about a year ago, ran some cleaner through fuel, and nothing until this weekend. So was reading through this. I will start with MAF sensor and throttle body first.

Is it not recommended to replace the manifold bolts when you replace gaskets? I had read that they rust off and fail?