Code p0171 & p0174

[Bigo Serge]

Hello fellas,
I'm having trouble figuring out what is causing these codes p0171 & p0174. I have a 2004 lq4 with a 4l80 in my 72 Cheyenne. I have replaced the intake manifold gaskets and could not find any leaks. I'm getting pretty frustrated with my research, so any input would be greatly appreciated. Could it be a weak fuel pump or sticky injector causing this? I have order a new relocating fuel tank with an in tank fuel pump from Boyd's aluminum tanks. Thanks. Sergio
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[68longhorn]

Yes it could be a weak pump. Do you have a regulator that is set to low? Are the pcv and breather hoses ok? To find a leak spray carb/tb cleaner around the intake and breather hoses and listen for a idle change. If no changes occur I would check fuel pressure. Are you still fuel injected? A faulty sensor could cause these dtc's too.

[Bigo Serge]

My fuel regulator is on the fuel rail, so I'm pretty sure it's ok, I'm running a cold air intake and I tried the intake cleaner spray trick with no idle changes. Yep, fuel injection.
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[BR3W CITY]

both are lean codes
do you have any leaks at the exhaust manifold, before the o2 sensor (would be a false lean condition then)

Otherwise if it is actually running lean, you can check to make sure the injectors are working, that your getting fuel pressure, and if you have done any aftermarket stuff, make sure it was properfly tuned

[68longhorn]

next step would be try a fuel pressure test.

[Bigo Serge]

Thanks for the input. I'm going to check the exhaust manifolds for leaks, and recheck my regulator, injectors, and pressure. Thanks again I'll keep you guys posted with what I find.
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[scss02]

Make sure the 02 Sensor are on the correct sides. If they are swapped it can cause this problem. Also make sure the ground wires on the back of the motor are secure. And make sure that you do not have cracked exhaust around the 02 sensor. I went through this, it ended up being a loose connection to the injector harness plug.

[clinebarger]

Ive seen alot of cracked intakes on wreaking yard pullouts, Usually right behind the throttle body "pad" on the bottom side of the intake.

Alot of the available LS engines were in accidents.

[Bigo Serge]

Thanks Im going to see if I can rent a smoke machine. I'll be surprised if its cracked, since my motor wasn't in a front end collision.
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[AMD6769]

Just had the same problem sunday it was the fuel pump check your fuel pressure 52-58 lbs is good

[Bigo Serge]

Thank you to all that had an input to my question. I have been checking what everyone mentioned off and on this past week. I found I had my exhaust manifolds needing retorqued, no vacuum leaks, but I did get my new Boyd custom gas tank and plan on installing it this weekend. So this will eliminated a weak fuel pump if I have one. Im still planning on checking my injectors to make sure I don't have a weak jet stream. Thanks again peeps and I'll keep you guys posted if I find something else.
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