Need Help diagnosing cause of code 44

[Kyle Baker]

Hi,
I drive an '88 C1500 with a 5.0L. I am getting the engine code 44, which I know is a lean exhaust condition, but I'm not really sure what's causing it.
I checked the EGR valve and it's working fine. I sort of suspect a bad O2 sensor, but I don't know how to know for sure.

What else are possible causes of this problem?
When I floor it to pass someone, and let off the throttle when I slow back down the check engine light comes on, but turns off after a while.

Thanks!
Kyle

[ChevyTech]

Anything that causes it to run to lean, or cause the ECM to detect that it is running to lean, will set the code 44.

A dirty fuel filter.

Low fuel pressure.

Melted or damage insulation, allowing the o2 sensor wire to come in contact with metal, grounding the circuit.

Exhaust system leaks ahead of or near the o2 sensor can allow extra air to reach the O2 sensor causing the code.

A.I.R. Air Injection Reaction (smog pump) system valve failure – on vehicles with this equipment.

A bad O2 sensor can cause a code 44, but usually a bad o2 sensor set a code 13.

[Kyle Baker]

I just replaced the O2 sensor to check that possibility and my problem remains.
Usually the CEL comes on when cruising at highway speeds and I let off the throttle to slow down, the light comes on then.
I'm going to try a new fuel filter next, but I don't feel any hesitation or anything, so I wouldn't think that it's starving for fuel... but you never know.
Also, my gas mileage is horrible...

[ChevyTech]

…I don't feel any hesitation or anything, so I wouldn't think that it's starving for fuel... but you never know.
Also, my gas mileage is horrible...

Look for something that is causing a false O2 sensor reading.

If I remember correctly there were 1988 TBI trucks that had A I R Pumps (smog pumps). If the valves controlling the air flow have failed it could cause this. There could be getting pumped in ahead of the o2 sensor in “closed loop” which should not happen.

Exhaust system leaks ahead of or near the o2 sensor can allow extra air to reach the O2 sensor causing the code.

[metalgod]

vacuume leaks as well get some gum cutter or carb cleaner and spray it around your intake manifold and vacuume lines the idle will increase if you got a leak check it hot as you were saying it happens on the road so opperating temp is where your problem is occuring

[colt45-2007]

Originally Posted by metalgod

vacuume leaks as well get some gum cutter or carb cleaner and spray it around your intake manifold and vacuume lines the idle will increase if you got a leak check it hot as you were saying it happens on the road so opperating temp is where your problem is occuring

I have an 88 C1500 with a 305 as well and I had the same problem, riding down the road at crusing speeds and the check engine light would come on and also had a higher idle, hooked it up and got a code 44 as well, sprayed carb and choke cleaner around the intake and the truck actually shut off instead of idling higher, checked vacuum hoses and had one with a hole in it, replaced it and its fine now