Code P0171 on 1998 GMC

[SuperCab]

Yeah yeah yeah, should have bought a Ford, but too late now.

For those of you more experienced than me in fuel injected systems, what are the common causes of a code P0171 - System too lean Bank 1?

It's not that the MAF is dirty, tried that already after reading that it is a common cause. There doesnt seem to be any vacuum leaks and the air intake snorkel seems tight from the filter to the MAF to the intake...

I'm somewhat at a loss as this Vortec (BTW It's a C2500 Suburban with 5.7L Vortec and 4L80E trans) is rather beyond my experience...


Any insight is much appreciated.

 

[5.0Flareside]

O2 sensor......

 

[smokey]

That code is mainly thrown from a vacuum leak.
Could be a clogged fuel filter or a bad injectior also.

 

[SuperCab]

Well it runs pretty much like crap... rough idle, no power...

 

[Blue Goose]

Well it runs pretty much like crap... rough idle, no power...

That's standard G.M. Factory equipment....

 

[blacksnapon]

Misfire on bank 1 will set a lean code for that bank.

 

[Truckin4life]

Sounds like vac leak too, have you checked the intake manifold?

I couldn't find the cause of a lean code on bank 2 for my truck...

Turned out that the mounting tabs for the upper intake had broke and i had a vac leak... haha

 

[73F100Shortbed]

O2 sensor......

Please don't suggest this as a first thing and have someone rush out and spend money on oxygen sensors. These things are not cheap. I can't even begin to tell you how much people have spent on their cars from reading this on the internet and it is a simple broken vacuum line. I'm not pointing this out to knock down your suggestion because it is a possibility, but certainly not the most probable one. Almost the last thing that will ever cause the lean code. I would make sure you don't have any misfire like Vince suggested with a scanner that shows misfire monitors. I would also check for vacuum leaks like suggested. Since it is on bank one only and I'm pretty sure the pcv valve is on that bank just like the 6 cylinders I would check the hoses starting there. Another possibility is intake gaskets, but if you can't find a vacuum leak before getting this far I would recommend finding someone with a smoke machine to check the gaskets for you. It is money well spent to save you labor if it is not the intake gaskets.

 

[blacksnapon]

One of the first classes I attended for Ford, that was one question that was presented to 20 of us in the class. "If theres a misfiring plug, will the o2s read rich or lean?" All of us said "Rich". Instructor said "WRONG! The o2s read oxygen, not fuel. During combustion, oxygen is consumed. No combustion, o2 levels are high. Thus, a lean code.

 

[DNFXDLI]

That's standard G.M. Factory equipment....

 

[5.0Flareside]

i said O2 sensor simply cause he said it didnt seem to have any vaccum leaks and a few other things... theres other things you can do that just replace O2 sensor.. you could unplug it... and see where the quality of running goes from there..

 

[73F100Shortbed]

i said O2 sensor simply cause he said it didnt seem to have any vaccum leaks and a few other things... theres other things you can do that just replace O2 sensor.. you could unplug it... and see where the quality of running goes from there..

Not likely that he will notice a change in how it runs from unplugging it other then set a code. Only time ever that I saw an oxygen sensor cause weird issues was when someone wired a universal one in backwards.

 

[6L PWR]

I have a 2001 Yukon with the 5.3L in it that gave that code. My buddy took a can of ether and sprayed around the intake while it was running and found the intake gasket leak real quick! Simple test.

 

[SuperCab]

Well, Vince nailed it. Had a misfire on bank one. For those of you not familiar with the gen1 vortec's distributor cap, it is a silly thing with all 4 wires for a bank lined up next to each other.

Like so:

Mine was burned through where the embedded thingys in the top of the cap are close to each other on the center 2 cylinders on the left side. New Dizzy cap fixed it. Thanks guys. Oh, and bite me Brad. That is all.

 

[73F100Shortbed]

Hope you used an ac deLco cap and rotor. Aftermarket ones are junk. Been there done that.

 

[SuperCab]

Seriously? Oh crap, cause I used a ... I think it was a Wells... whatever OReillys had... So i should expect a short service life from this one or??

 

[73F100Shortbed]

Maybe you will get lucky and not have an issue. I'm sure many times it is just fine, but I've seen it enough times that I just go with the ac delco ones to avoid changing them again. If your issue happens to come back I would start there. If it is running fine see how it goes.