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Bank 1 and 2 lean

Bank 1 and 2 lean

Postby Odinvalk [OP] » Feb 21 2021, 7:48pm

Seems all my issues with my truck all come at once. Was having an issue with an oil leak from my valve cover and noticed at the same time that I have change engine codes P0171 and P0174. I have checked for vacuum leaks and come up empty, my mass air flow sensor seems to be working properly, and my purge solenoid seems to be working properly. However I'm curious, over the last week down here in Houston we had a major freeze and power loss all over the place. Gasoline had a bit of a shortage. Normally I fill up with mid-grade, but twice I was forced to fill up with premium and regular on one or two occasions. I'm wondering if this sudden change in octane might have caused part of the issue?
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Re: Bank 1 and 2 lean

Postby Chevy-SSChevy-SS is online! » Feb 21 2021, 8:01pm

Here's a short vid (I watched it) with some good ideas: https://www.youtube.com/watch?v=jzT3M8hExuo

Additionally, the MAF could be acting up. I would remove it and clean it immediately, just to eliminate it from list of possibilities. Get the appropriate cleaner and give the MAF about 10 good, heavy sprays, right into the little wires, but don't touch them, they are incredibly fragile. Here's a short vid by the famous (and funny) Scotty Kilmer on cleaning a MAF: https://www.youtube.com/watch?v=xQGSkWEC_u4 Obviously, your MAF doesn't look like the one in the vid, but same principles apply!
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Re: Bank 1 and 2 lean

Postby SpeedyGonzalez » Feb 22 2021, 5:10am

Octane won't affect anything, but cooler ambient temps usually reveal failing intake gaskets. If your scanner lets you do live data reads, check out your long term fuel trims during a cold start and after it reaches operating temp, if it's much lower at operating temp then time to do the intake gaskets.
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Re: Bank 1 and 2 lean

Postby Odinvalk [OP] » Feb 22 2021, 4:29pm

Do you think aftermarket intake gaskets could fail and only a year? When I did the DOD delete on my truck I replaced the intake gaskets as well as the head gaskets and exhaust and everything else. I do hear a hissing from the top end of the motor, but I don't think it's a vacuum leak. I sprayed ether all over the place yesterday and never heard the tell-tale signs of a vacuum hose sucking in ether. I suppose it could be blowing air out between the intake and the head.
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Re: Bank 1 and 2 lean

Postby SpeedyGonzalez » Feb 22 2021, 4:41pm

Did you use the good felpro gasket set? It's not likely to have failed in a year so there's a good chance we can dismiss that. It's not always the intake gasket, the injector O-rings can dry and crack causing a random misfire, and lean codes that even the dealerships tend to miss(don't ask me how I know). With modern engines you can't spray the intake and listen for the RPMs to jump, the ECM can and will compensate for it, you have to monitor your fuel trims while spraying to identify the leak, you'll see a sudden drop in the long term and negative values for the short term.
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Re: Bank 1 and 2 lean

Postby LoudQ » Feb 25 2021, 6:25am

I’ve been having the same codes come up! And I have an oil leak from the back of my engine but it’s my oil sending unit, or oil pressure sensor. Could that oil sensor be the reason I am throwing the same codes you are? Its also throwing an evap code
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Re: Bank 1 and 2 lean

Postby SpeedyGonzalez » Feb 25 2021, 3:43pm

An OPS will not cause a lean code, the are completely unrelated systems unfortunately. If you have an evap code, your hardtube to the EVAP purge solenoid may be broken or cracked or your gas cap could be leaking, the cracked purge tube could cause lean codes if your purge solenoid is stuck open or clogged. Either way, start a new thread and we'll be able to get you more in depth help.
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Re: Bank 1 and 2 lean

Postby Odinvalk [OP] » Feb 27 2021, 4:01pm

So it seems that my issue was fixed by doing 2 things. One, my driver side (odd number) side of the engine, the valve cover gasket was dry and cracked, leaking oil. As well as the vacuum line from the booster to the intake was worn out. The rubber was soft and causing an issue. Not sure how either of those lead to a lean fuel air mix. But the codes went away after replacing.
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Re: Bank 1 and 2 lean

Postby SpeedyGonzalez » Feb 27 2021, 4:14pm

The driver side valve cover is the vacuum side of the PCV system, if it was leaking and sucking air in, that will register as unmetered air and cause a lean code.
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Re: Bank 1 and 2 lean

Postby FoxProDenali » Feb 27 2021, 4:29pm

Odinvalk wrote:So it seems that my issue was fixed by doing 2 things. One, my driver side (odd number) side of the engine, the valve cover gasket was dry and cracked, leaking oil. As well as the vacuum line from the booster to the intake was worn out. The rubber was soft and causing an issue. Not sure how either of those lead to a lean fuel air mix. But the codes went away after replacing.


Because the ECM is looking at air in (MAF) and air out (pre-cat 02) to set the fuel trim. So you were lean on both sides of the engine due to the vacuum leak. I guess.
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