sloppydawg123

It is a 97 4.3 vortec, but only runs in open loop, and runs lean at that.
What makes the engine switch to closed loop?
And shouldn't it run rich in open loop?

cam3439

I would think that it would run rich in an open loop. Have you checked your O2 sensors? Your truck should run open loop until the O2 sensors warm up and tell the computer if your truck is running too rich or too lean.

sloppydawg123

the o2 sensors say it's running lean in the open loop, and it never goes to closed loop

cam3439

What I meant to say is have you changed out your O2 sensors? They might be bad. If I remember correctly, the computer runs open loop at start up and goes to close loop once the O2 sensors give a reading back to the computer. From here the O2 sensors' readings will tell the computer if you're too rich or too lean. And I don't know what to tell you on running too lean. I think that the O2 sensor is giving a false reading (on account of it being bad) and is also the reason why it's staying in an open loop. How many O2 sensors do you have?

sloppydawg123

4 o2 sensors, the readings they send back to the scanner say bank 1 is lean

maxxman04

most o2 sensors are heated by an electrical current. the truck will run in open loop until the sensors reach a certain internal temp and send a signal to the computer. as long as sensors are good, the computer will switch to closed loop once it receives the signal. vacuum leaks, worn o2 sensors, bad plugs/wires/cap/rotor can cause ecm to run open loop while it searches for the proper signal. if your rig has over 100k on it and you don't know when the last time they were changed, change them.

sloppydawg123

after all that i found a cut in one of the wires off the o2 sensor, fixed the wire, seems to have fixed the problems

maxxman04

that is sweet. funny how sometimes it's somethin small and simple like that. glad ya got it fixed

cam3439

nice.