Hi, this is only my second post on here, I have had my 2000 ZR2 4.3/5 speed Blazer since march and have loved it, but the day we drove it home we got a code saying banks 1 and 2 are running lean, we have replaced a ridiculous amount of stuff on the Blazer hoping to get it running better (hesitates right after initial startup but then goes away). We have replaced:
Fuel Pump
Fuel Filter (twice)
bank 2 O2 sensor and common O2 sensor (still getting bank 1&bank 2 codes)
catalytic converter
cap and rotor
spark plugs
Ignition control module
probably a few other things i'm forgetting

I realize a lot of people have had trouble with running lean but very few threads seem to have people come back and reply with what fixed it or if it was fixed at all, I have to drive the Blazer across the state in a couple weeks and want to get all its problems tracked down and fixed. All help is appreciated.

 

more info: just performed the regulated fuel pressure test and found that the pump maintains 62 psi then once the pump stops priming the pressure drops to 56 and after 10 minutes is down to 52 psi

 

Checking regulated pressure at the service port, only shows regulated pressure. That's not enough data to diagnose the fuel delivery system. This thread explains how to test it: https://blazerforum.com/forum/2nd-ge...eakdown-88305/


Post all 4 readings and we can help you analyze them.

 

Correct me if i'm wrong but the reading indicates that there's nothing wrong since it is only 3 psi from the specs and i believe the 3psi deficit is due to a fuel pressure test kit that's been used too many times before

 

If your fuel pump max output is 62psi, and the regulator is set for 65psi, all you'll see at the service port is 62psi, which is within spec for regulated pressure, but just over half of what max output pressure needs to be. Test results at the service port mean nothing if you don't know what pump maximum output pressure is.


EDIT: If the fuel pump maximum output pressure is low, fuel volume to the injectors will also be low, which will cause P0171 & P0174, (both are lean codes) to set simultaneously.

 

But the leakdown results were mostly acceptable and the fuel pump is two weeks old (it failed, I wasn't guessing and checking). I found a leak in the throttle body gasket from the cheap K&N intake a previous owner put on to gain "7.4 horsepower at //4600//rpm" The leak was downstream of the MAF sensor so the extra air could explain the lean codes. Thank you for the help, if this doesn't cure it I'll do a proper pressure test.

 

I have done some research on the O2 sensors and I found out that it is recommended that they be replaced in pairs if they have more than 40,000 miles on them. I had a code for bank one sensor one and replaced it.(169,000 recent purchase) no other codes showed. After finding out about the recommendation I replaced bank 2 sensor 1 and gained nearly 2 miles per gallon average !! That should pay for itself quickly ! Is the catalytic converter old or clogged ? Sea foam clean out may help.