P0174 code and fuel pressure question
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 80
Likes: 14
From: Huntington Beach
P0174 code and fuel pressure question please move ore delete if not allowed.
I have a 2001 Z71 5.3 and I am getting a p0174 code which I know is lean bank 2. I had a new fuel filter left over from my brothers truck so I tried that out and it made no difference. I also changed plugs and wires because they were old and the previous owner put in the wrong plugs.
I checked the o2 sensor mV with my scan tool and it shows that the mV bounce from 100-900 low to high I am not sure if that is normal or not.
I also checked my fuel pressure and I am getting key on 49 PSI and drops a small amount.
Idling I get 45 psi and when I raise rpm it drops to around 44psi.
When I unplug the vacuum line to the regulator the psi goes to around 54-56psi and stays constant with throttle.
I check the fuel pressure on my dads truck which is a 2004 and his psi was constantly 62 psi and I know the spec for these trucks is 58-62 psi.
My Long term fuel trims on both banks are maxed out at positive 25 and idle and when raising the rpm they seem to drop to around 14-18.
I have searched for vacuum leaks spraying starting fluid and brake cleaner and watching the fuel trims to see if they were affected and I did not see any change.
Also something I’ve noticed is when I shut down the engine the fuel pressure rises to around 52-54 psi from 44-46 psi
Could my low fuel pressure be causing the lean code?
Any help is appreciated. Thank you
I have a 2001 Z71 5.3 and I am getting a p0174 code which I know is lean bank 2. I had a new fuel filter left over from my brothers truck so I tried that out and it made no difference. I also changed plugs and wires because they were old and the previous owner put in the wrong plugs.
I checked the o2 sensor mV with my scan tool and it shows that the mV bounce from 100-900 low to high I am not sure if that is normal or not.
I also checked my fuel pressure and I am getting key on 49 PSI and drops a small amount.
Idling I get 45 psi and when I raise rpm it drops to around 44psi.
When I unplug the vacuum line to the regulator the psi goes to around 54-56psi and stays constant with throttle.
I check the fuel pressure on my dads truck which is a 2004 and his psi was constantly 62 psi and I know the spec for these trucks is 58-62 psi.
My Long term fuel trims on both banks are maxed out at positive 25 and idle and when raising the rpm they seem to drop to around 14-18.
I have searched for vacuum leaks spraying starting fluid and brake cleaner and watching the fuel trims to see if they were affected and I did not see any change.
Also something I’ve noticed is when I shut down the engine the fuel pressure rises to around 52-54 psi from 44-46 psi
Could my low fuel pressure be causing the lean code?
Any help is appreciated. Thank you
TECH Fanatic
Joined: Jan 2018
Posts: 1,250
Likes: 239
From: Dade City, Fl.
You Already checked for a few of the possible causes of the code. Here is a cut and paste of a site about the code...
What Is The Cause Of P0174?
- Dirty or faulty mass airflow sensor
- Vacuum leaks – PCV hoses, vacuum hoses, intake manifold gasket.
- Weak fuel pump
- Clogged or dirty fuel injectors
- Clogged fuel filter
- Exhaust leak
- Faulty oxygen sensor
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
If problem is at idle, most likely vacuum leak. Are intake gaskets original black plastic framed? First, watch or graph MAF and MAP sensor voltage to make sure nothing odd at idle. If sensor outputs good, pull intake. Gaskets are likely collapsed and not sealing when cold and get better as the heat up.
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 80
Likes: 14
From: Huntington Beach
Well I smoked my intake and found a leak at the EGR where it goes into the intake m. Fixed that and it brought my LTFT numbers down to 7-14%. Other than that I cannot find any other vacuum leaks? The Mac sensor is good and the o2 sensors are reading the correct mV between .200 and .900. Are my LTFT numbers more acceptable? The code hasn’t come back.
Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 80
Likes: 14
From: Huntington Beach
If problem is at idle, most likely vacuum leak. Are intake gaskets original black plastic framed? First, watch or graph MAF and MAP sensor voltage to make sure nothing odd at idle. If sensor outputs good, pull intake. Gaskets are likely collapsed and not sealing when cold and get better as the heat up.
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
LTFT acceptable. Not uncommon to have intake gasket leaks on inner/center area (under intake) and never see it with smoke or see STFT #s change with brake cleaner.
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Thread Starter
Staging Lane
Joined: Oct 2019
Posts: 80
Likes: 14
From: Huntington Beach
that may be the case. The light hasn’t come back yet so I might let it ride until I can get it smogged then do the intake gaskets. I just need the damned secondary air monitor system to finish then I can take it to smog
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