I have a 1996 blazer with a 4.3 that is throwing lean codes on bank 1 and 2 at random times. Its currently at a shop and they cant seem to find an answer as to why. Theyve gone through the fuel injectors, put a new fuel regulator and fuel pump on it as they thought it was from poor fuel pressure. Truck runs good, but keeps throwing the codes. They have hooked the computer up to it and took snap shots while driving it when it threw the codes but all of the readings are within normal range. They say that it is throwing them for a loop because all of the normal things that go wrong with these motors are turning up fine. Any help?

 

What DTC's are being set?
Any chance you can get the numbers from the freeze frame data and post them?

 

It's throwing p0171 and p0174. I do not have the exact numbers available as I am out of town. They stated it throws them when under closed loop as well but was o2 sensor and threw the codes most of the time when driving a distance. Around 40 miles at one time. I'm sorry for the lack of information as this is all new to me.

 

Sometimes brand new parts don't perform as they should, especially fuel pumps. I realize it's been addressed already but, one of the early signs of low fuel pressure and or excessive leakdown, is lean DTC's being set. Correct fuel delivery is critical with this injection system. Checking fuel pressure and leakdown is simple, free, and only takes about 15 minutes. It will tell us immediately if the fuel delivery system is functioning properly. Most auto parts stores rent/sell/loan fuel pressure testers.

Connect the tester to the service port: driver side, next to the distributor. When the ignition is initially turned to the RUN position, (engine off) the fuel pump is activated for ~2 seconds and then deactivated. Fuel pressure must be checked during that 2 second time frame while the pump is running. Pressure must be 60psi to 66psi. It must remain above 55psi for at least 10 minutes after the pump shuts off. Check it out and post your results.

 

After all of the researching and weeks without my vehicle while it was at a very reputable shop I picked it up on Saturday after they told me that they just couldnt put their fingers on the problem. I drove it off and it stumbled from idle on initial acceleration. I brought it home and grabbed a stethoscope that I use on the fire department and started listening to all of the vacuum hoses as I have had everything that deals with fuel replaced(equals a nice bill) and found the old pcv valve sucking air on the pcv boot. Bought both new rubber boot ends and reset the codes and it runs perfect and no more codes. Thank you for all your help!

 

Nice piece of investigative surgery! Glad you got her going, and thanks for posting back.