SES comes and goes.

I have a 96 blazer with a 4.3l vortec. My SES light has been on for a few months. When its scanned it comes back system bank 1&2 running lean. I have taken a few trips upnorth (about 235 miles) and the light when off but came back on in about 50 miles. Then a few weekends later I took another trip to the same place and the light went off before i left and stayed off until a few days after i got home. I would say a good 600 miles later. I am searching for a answer to this problem. Could the O2 sensors be triggering this code? Any solutions? Any help would be greatly appreciated! Thank You in advance.

What is the code No?

Bank 1&2 lean can be several things.
Low fuel pressure oor pluged fuel filter and or MAF sensor are leading cause of lean both bank codes.

Rule out 02 sensors unless both bank 1 & 2 sensors are bad at same time.

Any aftermarket air intake stuff or K&N filters?

Give use your fuel pressure raedings.

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 or hot and fuel pressure testing guide lines.
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.

Both codes came up at the same time. I am going to have it scanned again to get the exact codes. I do not remember them off the top of my head. I have a k&n cold air intake. I am planning on checking the fuel pressure regulator to see if it is washed out and leaking. and i would like to replace the injectors. The motor has 209K and I have a feeling the injectors are not 100%. I have been running some lucas fuel injector cleaner in the truck. I just feel it would be best to replace them. I replaced the fuel filter a couple of months ago and it was very black and clogged when i replaced it. Probably was the original. Can I get a fuel pressure tester at my local auto parts store? and I am not sure how to test the fuel pressure. Im a rookie! I have been learning alot as I go. (took me a couple days and alot of swearing to replace the intake manifold gasket when it went!) Also I have a high flow cat...and straight through muffler (not sure if this has anything to do with whats happening) The truck ran great after the cold air intake was first installed. Accelerated smoothly and i could not even feel the truck switching gears. Any help is greatly appreciated. Should I bother checking the fuel pressure before I replace the injectors? and are there different brands of injectors and nut kits and regulators available at a local auto parts store? I was also planning on just replacing the wires and pluges again. I am curious on what brand of plugs and wires to use as well.....! I have a lot of plans here. Just trying to make sure the truck lasts!

Injector cleaner does not do much good.

Only use AC delco plugs and the best wires and AC ddelco cap and rotor.

Set the K&N filter in back of rear wheel and back up and then drop it in the trash can.
Start with cleaning maf sensor with some carb or tb or maf sensor cleaner .

On the fuel pressure get one with a long hose and tape to outside windshield or outside rear view mirror.

The test port is on top rar of engine on fuel rail.

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 or hot and fuel pressure testing guide lines.
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.

I got the codes. The first code was a p0420-catalyst system efficiency below threshold (bank 1). the second code was p0442 evap system (small leak). The evap code has came and gone as well. The bank 2 didn't show up now. How can I find the leak? And I am going to test the fuel pressure tmrw!will post.
BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.1.20.06.3.1.20.0

Forgot to ask. Would you recommend I put the stock intake back on?
BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.1.20.06.3.1.20.0

Forgot to ask. Would you recommend I put the stock intake back on?
BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.1.20.06.3.1.20.0

Yes go back to OEM air intake/filter setup.

Also the high flow cat or 02 sensors may be giving problems on cat codes.
Are the 420 cat codes gone now?

Clean Maf sensor and check the fuel pressure real good.

On the evap leak start with a GM oem gas cap.

The fuel pressure is over 60 when I turn the key just to power. After I start the engine it ran at about 52 to 54. Drove around and when at idle at stop signs it was just over 50. When I turned the key off it dropped down to 50 and then rode to around 56 after 5 to 10 seconds. Did not lose pressure for the 20 to 30 seconds I gave it before I had to go into work. I checked the prssure and ran with the gauge on while it was connected behind the fuel rail. From these readings I believe I have a problem here since its not really comparable to the specs u gave me! I am going to cold start it again after work and drive home with the guage on again. Are there any other locations that I need to check the fuel pressure? And I believe I found a dry rotted line that goes into the evap canister. I will upload a pic after work.
BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.1.20.0

The fuel pressure is over 60 when I turn the key just to power. After I start the engine it ran at about 52 to 54. Drove around and when at idle at stop signs it was just over 50. When I turned the key off it dropped down to 50 and then rode to around 56 after 5 to 10 seconds. Did not lose pressure for the 20 to 30 seconds I gave it before I had to go into work. I checked the prssure and ran with the gauge on while it was connected behind the fuel rail. From these readings I believe I have a problem here since its not really comparable to the specs u gave me! I am going to cold start it again after work and drive home with the guage on again. Are there any other locations that I need to check the fuel pressure? And I believe I found a dry rotted line that goes into the evap canister. I will upload a pic after work.
BlackBerry8310/4.2.2 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102 UP.Link/6.3.1.20.0

If fuel pressure does not come up over 75-85 with return line blocked off.

Go to the fuel in line at fuel filter and hook direct to it and check fuel pump full pressure.
A good pump will jump to 95 to 105 lbs.
But do not run at full pressure ove a couple of seconds for the test.

Running pressure should be 60/66 at all times.
62-65 depending on engine load.
Cold start should be 65 lbs pressure.

If not check for where it is losing pressure.