Truck running lean out of nowhere.

[C&C Chevy]

I got in my truck today to go home from work. It starts up fine and then wants to cut out, but revs back up. The idle is very erratic, 700rpm to 1100rpm and back again. The truck stumbles all the way home, going about 25mph.

I get out my code book and it's giving me to codes. 24 and 44. 24 is a VSS malfunction. Not sure if this would effect idle. The code 44 is what has me worried. It's a lean condition. Where would be the best place to start? Fuel pump, FPR, other stuff????

I'm seriously thinking of taking it to a mechanic. If anyone knows a trustworthy mechanic in central Oklahoma, let me know!

also, should I worry about driving it to far? I know running lean is alot worse than running lean. Just don't want to blow up my 1 year old crate engine!

[grinch4om]

sounds like possibly a vacuum leak

[82c10]

Originally Posted by grinch4om

sounds like possibly a vacuum leak

yeah, it could be that, or it could be related to the weather we have been having

[j hannah]

might be a crack in the base gsaket under the throttle body, or other vacume leak. you might find it if you shoot some carb. cleaner around the gaskets.

[rfmaster]

I would start with Code 44 (engine lean condition) and address Code 24 after solving Code 44

I am assuming that you have 220-TBI on top of stock 350 crate motor.
First – clear all codes and address code 44 –stumble lean conditions

Code 44
According to GM trouble shooting guides code 44 relates to Oxygen Sensor circuit Lean condition indication. Code 44 is set when Oxygen sensor circuit (412) reads below 250mV for 50 seconds while system operates in closed loop.

If you have a scanner set scanner to Scan and observe when block learn numbers (BLM) at different RPM’s and air flow conditions to determine where Code 44 was set. The BLMs of 150 will cause Code 44 to be set.

What could cause 44

Check O sensor wires – make sure O sensor wire does not contact exhaust. Check sensor ground for a good contact. Check for intermittent contact between connector and sensor.
Make sure that O sensor ground is clean – use specially formulated anti seize compound.

Manifold Absolute Pressure (MAP) Sensor may cause ECM to see lean condition. Temporarily disconnect MAP sensor and if the lean condition is gone replace MAP sensor – around $50.

Lean Injectors: check for fuel contamination such as water in the fuel may set code 44
Check fuel pressure
Exhaust leaks will cause code 44 by letting outside air into the system upstream from O sensor and cause sensor to see lean condition.
Check AIR system – if air pump is injecting air in exhaust when operating in closed loop this will cause O sensor read very lean.


I hope it helps.

//RF

[Farmer Mike]

Dude, Do the easy stuff first. Replace your fuel filter if you can't remember the last time you did it. Give the old filter a good inspection to see if there's any rust accumulated or a giant ball of goo that's hindering flow.

Mike