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P0171 and P0174 CEL lean code on both banks.


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#1 Tyson06SS

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Posted 17 March 2017 - 09:29 PM

 I have had a CEL on and off on my dash for 2 months now. I have cleared the code and it comes back on. My scan tool says its a P0171 & P0174 lean bank 1&2. I have cleaned the throttle body, replaced the MAF, replaced the intake manifold gaskets, replaced the K&N air filter, replaced the front O2 sensors and the spark plugs with NGK TR55IX. I am at a loss with the CEL code. The truck only stumbles at stop signs/lights and when backing up or any other time at low RPM's. My truck is a 2006 Silverado SS with 157,XXX miles and the return-less style fuel system. I have been told that I may need a new tune because it is 4 years old. My mods are 1 7/8 LT's, Kooks High Flow Cats, True Dual exhaust with a x pipe, 4L80E swap with a FTI 2800 single disk converter, K&N air intake, 40K Tru-Cool with -6 nylon braided high pressure hose. Like I said it has been tuned but that was in 2013 by RPM Performance in Garner, NC. I have also replaced the battery (Interstate), alternator (Nations starter & alternator 165 AMP), starter (OEM), brake booster (OEM) and added a PCM of NC larger gauge power cables. I need to replace the master cylinder which is still hissing at a stop from being OEM equipment. I have a TBSS intake, throttle body, and fuel rail with fuel injectors and pigtails. My plan is to fix the problems with the truck, install the complete TBSS intake, LS2 243 heads with PAC 660 springs and a BTR stage 4 truck cam. I will have it retuned with all mods, but right now I'm trying to get this lean code to go away. 

Any help would be awesome.

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#2 1BAD2K

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Posted 17 March 2017 - 09:39 PM

You say master cylinder is hissing? You think you're hearing a vacuum leak? That could cause a running lean issue.
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Current build: 2006 RCSB 4x4 - LS6, magnacharger, 4l80e, circle D, hydroboost, corsa, arh, beltech, coilovers, nvg149, baer+z06 upgrade, intro wheels... full on SS clone in the making.

#3 EXGM

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Posted 17 March 2017 - 09:55 PM

That or a intake leak.... to test intake get a can of brake clean. Slowly work your way down one side spray a little brake clean where intake meets head. If RPM increases you've found the leak.
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#4 Tyson06SS

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Posted 17 March 2017 - 10:46 PM

It's a vacuum leak from the brake booster, not master cylinder sorry. I think either the brake booster is bad or it wasn't a good reman from the start.
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#5 Downeast Johnny

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Posted 17 March 2017 - 11:02 PM

My guess is that 1Bad has it figured out.  The vacuum leak will do it.  Good excuse to go to a hydroboost set up.


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#6 Rocky81

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Posted 21 March 2017 - 03:59 PM

It could also be your computer is reading the alcohol content in your gas too high. I just had the same issue. Had the computer reset to 3% alcohol it was reading 60 at the time. Issue resolved.
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