O2 Sensor issues

[mpyusko]

Normally this isn't a problem day-to-day....

Whenever I am towing a heavy (3,000 lb+ load) my foot stays into the pedal a bit more. So when climbing hills or accelerating to highway speed, the RPMs stay up higher for a longer time. With almost a predictable timing, these 2 fault codes will always appear. If I don't clear them, then my power is halved the next time I start from a stop. So I use the Torque app and a bluetooth controller to log all my sensors, automatically check and then clear the fault codes.

In the past 2,000 miles, I've replaced the cap, rotor, plugs, wires, TPS, IAC and EGR. The air filter is a K&N so I washed that too. The injectors have about 260k on them and are on my list to be replaced. The engine only has about 60k (GM crate motor).

Thoughts?

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[geeeee89]

did you replace the O2 sensors?

 

[kennythewelder]

Bank 1 is drivers side, bank 2 passengers side. Both showing low, do you have exhaust leaks? Looks like an over lean, or over rich condition. You would have to see the fuel trim levels to figure out what one. I get the same code when I have a header leak, but mostly on one side. When is the last time you replaced the 02 sensors?

 

[Supercharged111]

Low voltage = lean. The fact that both are showing lean makes me think the O2s aren't lying. Check your fuel pressure and see if you can even blow through the fuel filter.

 

[stutaeng]

Oh, I didn't know low voltage on these meant lean...

On your app, look at the O2 graphs, specifically the upstream ones. Spray a bit of carb cleaner on the intake tube and look for a change in activity. That's an easy way to see if the O2s are responding.

So you don't have lean codes? Just these 2? I've seen where sometimes there are intermittent O2 sensor codes, but it was caused a real (not perceived) lean condition, but I also had a real lean condition (again, not a perceived lean condition.) You should also look at fuel trims.

 

[Supercharged111]

Low voltage is lean, around 450-500 mV is stoich, and high voltage is fat. The range is 0-1000 mV.

 

[Dariusz Salomon]

I read somewhere that the ground on the engine close to the crankshaft position sensor is responsible for o2 sensors and can throw codes sometimes. And I don't think it's ypur case but maybe worth checking too.

 

[Schurkey]

My '88 K1500 uses a much less-sophisticated computer system. There is only one O2 sensor.

I got a "lean" code every time I got to highway speed. At first, it wouldn't set until ~65 mph (depended some on wind direction.) As things got worse, it set the code at lower and lower speeds.

"Everything" seemed to test fine. I dicked with this for two years, on-and-off. Fuel pressure good, AIR system diverting like it should, nice injector spray, good O2 crosscounts at lower speed--but zero crosscounts at higher speed, coupled to rich-command of the fuel system. Gas mileage was poor.

In desperation, I put in a new O2 sensor.

Problem solved. I still don't know why the sensor showed a false "lean" voltage at higher speed/heavier load--but it did. It was only about 70K--80K miles old.










PS: DO NOT wash a K&N or other "oiled gauze" air filter unless there's an eighth-inch build-up of dirt on it. Washing an oiled-gauze filter is the worst thing you can do to it. They filter better when they're dirty than when they're clean. NOW, K&N recommends an air filter restriction indicator to determine when the filter should be cleaned. Years ago, they just said "1/8 inch of dirt". I've seen the instructions that came with the huge K&N air filters used on City Bus diesel engines--they said that the "dirty" filter may need some additional filter oil, applied from the CLEAN side, but if the restriction indicator wasn't showing a flow problem, DON'T WASH IT. Basically, if you can see the pleats, don't wash it.

 

[stutaeng]

I think they get "laggy" when they get kinda old. I'm not sure how one would test that, however. Probably just replace 'em as you did.

BTW, Rockauto has the best prices on these!

I'd still verify they are faulty first though. Seems somewhat unlikely both are bad.

 

[HotWheelsBurban]

My 99 Burb is a 5.7, but here's my experience with the O2 sensors. I've had this truck 8 years, most of its use in the last 4 years. I've replaced the downstream ones twice in that 4 years, when I had codes indicating they were bad. Replaced the front one on driver side ( bank 1) last year because it was coding bad. Original unit to best of my knowledge.
Now I'm getting codes for bad O2 sensors, bank 1,sensor 1. Which would be the one that's the newest one on the truck. I would have thought that if one was bad, it'd be the passenger side upstream one, since it's original. Only one that hasn't been replaced. My inspection guy hasn't been able to get a good reading on his scanner yet; it keeps saying that the systems are" not ready to scan", hence no data available to give more indication of the exact problem.
Any hints? I'd like to get this Burb inspected and registered, so I don't have to watch out for picky police! Thanks in advance!