system lean codes

[truckdude239]

ive been battling p0171, p0174 syatem lean bank1 and bank 2 i've already replaced the intake gaskets, i do not have a brake booster but i have the van plug in the back of the intake not leaking, ive cleaned the mass flow air sensor, no change will set lean codes after about 30 mins of driving, fuel pressure is 60psi, so im left with either a bad mass flow or 2 bad oxygen sesnors whats the best way to tell which i need without throwing parts at it? motor is a 2004 silverado 4.8 4l60e running an corvette filter and ac delco ep381 fuel pump.

[zach_carver]

I was having the same issue but my tuner found my my injectors were nasty/dirty not working correctly. I replaced my injectors and got me all fixed right up.

[87chevy.com]

maybe smoke test the intake system.. if ok, install a windeband setup
clint

[rodstored-72]

I am not getting a lean code ...yet, but according to the guy that rebuilt my engine ('13 gen IV) he & the tuner indicated that the engine is running lean, I had the injectors cleaned & tested, but it is still "lean popping" I am running the same FPR/filter and the same fuel pump (EP 381) with approx. 54-56 fuel pressure.

would like to know more on the suggestions by Clint??? maybe for me to try as well

thanks!

[87chevy.com]

if its reading lean, off the top of my head it could be a few things
air leak? smoke test would be ideal.. this little smoke machine is pretty bad @ss... few techs have these at work they put out a lot of smoke which is good. they feel light duty, but they work:
Smoke Machine link on Amazon

maybe try CRC Mass Airflow cleaner, or CRC electric cleaner.. maybe aftermarket oil'd air filter contaminated the Sensor?

If no intake leak, then check fuel pressure.

If fuel pressure is good, check fuel flow... not sure what the spec is, but you can have good pressure, but low flow... like collapsed fuel line or clogged injectors.... pressure will be good up to the clog...

Another thing to check is Ethanol content.. theres some simple kits to check... if you have a lot of ethanol in the fuel, that could be a cause for running lean.

if no air leaks, good fuel, good fuel pressure, and good flow, maybe look into the tune? Before going to tuner, I would have a wide band installed and look at the readings before you go, so you can know for sure that its running lean, and when you get it back from the tuner, you can look at the same gauge, and see its fixed.

I can imagine, some will just just skip smoke testing and say yes, no air leaks and just skip over to its the tune, but when you go to the tuner, they will charge you for their time.. mine as well just do everything you can do before you go to them

side note, if you have a card style mass airlfow sensor, if the tube that its mounted in is not the exact same diameter as OEM, it will run poorly... I found that out on my l83 87.... forget which way the readings went, but it went max one way, rpms were way low.... clear adaptions, idle restored for a few seconds and then would run poorly again....

another side note, is the mass airflow sensor factory? aftermarket? wheres the mass airflow sensor.... it should be about 12" or away from throttle body if I recall correctly... to close and it gets some funky readings.

this is what I would look at if it were a car in my bay at work.
clint

[truckdude239]

Originally Posted by 87chevy.com

if its reading lean, off the top of my head it could be a few things
air leak? smoke test would be ideal.. this little smoke machine is pretty bad @ss... few techs have these at work they put out a lot of smoke which is good. they feel light duty, but they work:
Smoke Machine link on Amazon

maybe try CRC Mass Airflow cleaner, or CRC electric cleaner.. maybe aftermarket oil'd air filter contaminated the Sensor?

If no intake leak, then check fuel pressure.

If fuel pressure is good, check fuel flow... not sure what the spec is, but you can have good pressure, but low flow... like collapsed fuel line or clogged injectors.... pressure will be good up to the clog...

Another thing to check is Ethanol content.. theres some simple kits to check... if you have a lot of ethanol in the fuel, that could be a cause for running lean.

if no air leaks, good fuel, good fuel pressure, and good flow, maybe look into the tune? Before going to tuner, I would have a wide band installed and look at the readings before you go, so you can know for sure that its running lean, and when you get it back from the tuner, you can look at the same gauge, and see its fixed.

I can imagine, some will just just skip smoke testing and say yes, no air leaks and just skip over to its the tune, but when you go to the tuner, they will charge you for their time.. mine as well just do everything you can do before you go to them

side note, if you have a card style mass airlfow sensor, if the tube that its mounted in is not the exact same diameter as OEM, it will run poorly... I found that out on my l83 87.... forget which way the readings went, but it went max one way, rpms were way low.... clear adaptions, idle restored for a few seconds and then would run poorly again....

another side note, is the mass airflow sensor factory? aftermarket? wheres the mass airflow sensor.... it should be about 12" or away from throttle body if I recall correctly... to close and it gets some funky readings.

this is what I would look at if it were a car in my bay at work.
clint

do not have a vacuum leak as i do not have any vaumn lines hooked up and i replaced the intake gaskets, and have had my friend at a local shop smoke it to verify mass flow is a factory sensor that came with my swap many many moons ago and has been cleaned fuel pressure is good the truck runs great and has awesome power i have a cold air intake that the factory mass goes on the end of it and then the filter to the mass flow

[87chevy.com]

maybe next step set up a wide band and see what it reads and see if it confirms of conflicts with what the PCM is reading

[cj847]

I am curious what you found as the final solution.

I had a situation where my LTFT was +25 both banks. Couldn't find any vac leaks. Checked live data and was getting believable readings from O2, MAP, and MAF.

I pulled a MAF off of another vehicle and installed it. LTFT immediately improved to +8 to +15 range. Apparently the MAF was giving a reading, it just wasn't correct, no matter how much I cleaned it.

[truckdude239]

Originally Posted by cj847

I am curious what you found as the final solution.

I had a situation where my LTFT was +25 both banks. Couldn't find any vac leaks. Checked live data and was getting believable readings from O2, MAP, and MAF.

I pulled a MAF off of another vehicle and installed it. LTFT immediately improved to +8 to +15 range. Apparently the MAF was giving a reading, it just wasn't correct, no matter how much I cleaned it.

I have not even messed with it i do have a new dephi maf i need to install i just havent had the chance to yet

[truckdude239]

Update my fuel pressure was dropping to 35 psi under load, installed new ac Delco vette filter and Delhi pump fuel pressure now have 65psi at the rail all the time truck runs so much better I belive it's fixed but I got t9 put more miles on it now

[rodstored-72]

TRUCK DUDE, Thanks for the update, how "old" were the pump & filter? and would you share the pump model (info)? I may look into replacing my pump as well.
thanks!

[truckdude239]

They are about 15 years old I used a rear suburban tank from 87 with an ac Delco ep381 pump

[rodstored-72]

oohh.. ok, I have new tanks, pumps & filter (ep-381 & corvette style). glad the issue is resolved for you....