TBI running lean?

[Spacecwboy]

ck engine light comes on after 3-5 minutes of running, checked it and the code says the engine is running lean. What can I do?

92 Chevy 4.3L TBI
Painless harness

[86k30]

Check fuel pressure
Check for vacuum leaks
Check for partially open EGR valve
Check to be sure you dont have watered fuel

[ray1377]

Get some starter fluid in a spray can.
While the engine is idling, spray the starting fluid at the base of the TBI right where it bolts to the top of the manifold.
Listen for any change in engine RPM, (engine speeds up a bit)
If it does, you may have a leaky TBI intake gasket.
You could try tightening the TBI bolts, it might work a bit, but the gasket will need to replaced.
Ray

[FrankenToy]

Ensure that you are, indeed, running the correct O2 sensor. Just because it screws into the threaded opening in the exhaust doesn't mean it'll function correctly. My 2.5L IronDuke needed a new O2 sensor after 250K miles (just barely failed emissions test). I went to a GM Chevy dealership and purchased a brand new AC-Delco replacement. It was not the right one. IIRC the ECU needs to see a signal that toggles from rich to lean something like 30 (?) times a second. The incorrect O2 sensor didn't provide a quick enough toggle rate and the computer tried to over-compensate on either the fat side or skinny side. My truck ran like crap with the wrong O2 sensor and threw a lean code, too. I needed to use a scanner that showed the transitions from lean to rich per second to determine that I had the incorrect O2 sensor. Turns out that Vato Zone had the correct Bosch unit cheaper (I really wanted another AC-Delco sensor because the previous one lasted 20 years).
Just my experience.

[buzzbomber]

judging by the time it kicks the ces light on its when its going closed loop so the first thing i'd look into is an o2 sensor. bosch part #12014 and about a dozen gm part numbers

[MrWillys]

It probably wouldn't throw a lean code from a bad O2 considering the O2 is what help set the code. Put a scanner on it, and check the BLM counts. Lean would be from about 130 to 160, and rich from 126 to 108. Perfect blm is 128.
As has already been suggested, you probably have a fuel issue. Dirty filter, bad fuel pump, bad injector, or even a kinked fuel line. Timing not been set correctly could also set this code.

[FrankenToy]

Originally Posted by MrWillys

It probably wouldn't throw a lean code from a bad O2 considering the O2 is what help set the code. Put a scanner on it, and check the BLM counts. Lean would be from about 130 to 160, and rich from 126 to 108. Perfect blm is 128.
As has already been suggested, you probably have a fuel issue. Dirty filter, bad fuel pump, bad injector, or even a kinked fuel line. Timing not been set correctly could also set this code.

It will most certainly throw a lean code caused by an incorrect O2 sensor. Not trying to start a fight but it definitely will throw a lean code. The things you've listed could be factors also, not disputing...

[KacksterK5]

O2 sensor, my old TBI did that. Changed the O2, good to go

[Spacecwboy]

i will try. that is weird is that it runs great. only a few times has it stumbled but it was not at a time when I had the ck engine light. i will pick up a new o2 sensor and see what happens

[buzzbomber]

Originally Posted by Spacecwboy

i will try. that is weird is that it runs great. only a few times has it stumbled but it was not at a time when I had the ck engine light. i will pick up a new o2 sensor and see what happens

thats because it's probably returning to open loop and getting its a/f from the CTS.

[MrWillys]

If you would scan the blm counts you could eliminate other possibilities, but guessing will solve it eventually.

[beefdawg]

Originally Posted by ray1377

Get some starter fluid in a spray can.
While the engine is idling, spray the starting fluid at the base of the TBI right where it bolts to the top of the manifold.
Listen for any change in engine RPM, (engine speeds up a bit)
If it does, you may have a leaky TBI intake gasket.
You could try tightening the TBI bolts, it might work a bit, but the gasket will need to replaced.
Ray

Starter fluid is pretty risky. Use something safer like WD-40, or carb cleaner.

[gmcxt]

Originally Posted by Spacecwboy

ck engine light comes on after 3-5 minutes of running, checked it and the code says the engine is running lean. What can I do?

92 Chevy 4.3L TBI
Painless harness

What is the code?

[Spacecwboy]

44

[MrWillys]

http://www.chevythunder.com/o2_sensor_code_44.htm

[jake666]

id lean to a 02 also obd1 isnt very smart so it really cant self dio something else to check to is the vac line goin to the map sensor the end at the tb likes to crack or suck shut . typically it makes the motor really rich since the map vac goes low but like i said obd1 isnt very smart and getting a lean coade can happen from that , also check ur pcm block grounds. by the water neck and the rear of the head. the o2 relys heavy on a decent ground a high restaince ground can cause all kind of issues .its funny tbi is so much simpler but seems to be a bit harder at times to trouble shoot lol