1990 gmc sierra lean exhaust code 44

My truck out of nowhere will start to idle low and die when put in reverse or drive then on other days sometimes it will start and run right. I got the code 44 witch it could be a o2 sensor but tomorrow I’m getting my catalytic converter took off and run straight pipe do I still need a o2 sensor without a catalytic converter or what’s causing lean exhaust?

May we assume you live in an area with absolutely no smog inspections of any kind?

No they don’t inspect here

I can think of no good reason to straight-pipe your truck.

Your code is probably caused by a failing O2 sensor, but any competent mechanic should be able to test it and the rest of your fuel and ignition system and determine the cause of your poor running and check engine light.

Or just replace the sensor and see if it fixes it. They’re dirt cheap.

Code 44 is a lean code. Could be an O2 sensor but most likely it’s the fuel pump. Fuel pressure needs tested. Specs are 9-13 psi. Deadhead pressure should be 18-20 psi. These vehicles have had a problem splitting the fuel hose between the fuel pump and the pipe in the tank allowing the fuel to get pumped directly back into the tank. Removing the cat will most likely not help your situation, not to mention even if you’re not in an inspection state if the EPA discovers there’s no cat there will most likely be a hefty fine.

The code 44 for lean exhaust is most likely caused by one or more of the following:

1.) O2 sensor wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.

2.) Check for an intermittent ground wire between connector and sensor.

3.) Poor ECM to engine block ground.

4.) MAF Sensor - A MAF sensor that causes the ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect the MAF sensor. If the lean condition is gone then replace the MAF sensor.

5.) Vacuum leaks can cause a lean condition and/or possibly a high idle. Check for cracked hoses a bad gasket or a faulty EGR or PCV Valve.

6.) fuel pressure - system will go lean, if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm.

7.) Clogged injector or lean injector - perform an injector balance test…

I would say 4-7 are more likely than 1-3

Number three is a very likely culprit at the T-stat housing. Number four does not exist on this vehicle. Number six is the most common on this vintage from my experience of thirty plus years as a mechanic. If this thing runs bad as soon as you start it, then the oxygen sensor can not be the problem. It doesn’t rely on the O2 sensor til it goes into closed loop, which on a single wire O2 is quite a while. Like a minute or more. The O2 sensor has to “light up” before it starts generating voltage, which is what the ECM looks for to put it in closed loop.

Re: needing an o2 sensor w/o a cat

I’m presuming you mean the pre-cat o2 sensor*

Yes, the o2 sensor is still critical, used by the ECM to adjust the fuel to air mixture when the engine is warmed up. W/ no o2 sensor you’d always be running in what is called “open loop” mode, which could cause engine overheating if running too lean, even burnt valves, or if running overly rich, excessive carbon deposits and poor mpg. Plus the check engine light would be on all the time, which is bad b/c if another problem crops up and the ECM tries to tell you about it, you wouldn’t know it.

*In some newer vehicles there’s two o2 sensors, one before the cat, and one after. It is the one before the cat that the ECM uses to adjust the mixture. The one after the cat is used to monitor the cat’s performance.

So if this truck doesn’t have a MAF sensor, it either uses speed density, or it’s got TBI . . .

As far as oxygen sensors, I personally doubt it’s got a downstream sensor, based on the age of the truck