Codes 0171 and 0174

[stick64]

These lean codes are popping up now on my 4.3 with 180k miles on it. Recently I changed out cat, fuel pressure regulator, and cleaned MAF sensor. Would any of these changes cause these codes to come up ? thx

[MT-2500]

Originally Posted by stick64

These lean codes are popping up now on my 4.3 with 180k miles on it. Recently I changed out cat, fuel pressure regulator, and cleaned MAF sensor. Would any of these changes cause these codes to come up ? thx

Yes and no.
What year make and model and engine?
The codes say lean on both banks.
Start with a good fuel pressure test.




The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[stick64]

"Yes and no.
What year make and model and engine?
The codes say lean on both banks".

2000 S10 Blazer 4.3, The code reader I have flashes 0171 and 0174 only. I do not know about both banks. Ah, failed to mention with initial post that I replaced fuel pump and filter 6k ago. Thx

[MT-2500]

Originally Posted by stick64

"Yes and no.
What year make and model and engine?
The codes say lean on both banks".

2000 S10 Blazer 4.3, The code reader I have flashes 0171 and 0174 only. I do not know about both banks. Ah, failed to mention with initial post that I replaced fuel pump and filter 6k ago. Thx

Both banks is all cylinders on right and left side of engine
One bank is cylinders on one side.
Both banks = The complete fuel system or hole engine engine is running lean.
Can be caused by several things.

I would start with a fuel pressure test and check that fuel filter.
Post back fuel pressure readings and we can go from there.