O2 normal voltage

[Qball]

Hey I was just wondering what normal voltage should be for o2 sensors mine seem a bit low. Downstreams tend to hang below .4v usually around .1 to .3

 

[PlayingWithTBI]

Downstreams tend to hang below .4v usually around .1 to .3

That looks to be running too lean. Stoich or Lambda 1.0 s/b ~.45v. What are your upstream sensors showing?

 

[Qball]

Upstreams on average seem to be hanging around half a volt tho I will see them go rich for a few seconds then go lean.

 

[stutaeng]

I think the upstream should oscillate in a sine-curve between 0.1V and 0.9V (theoretically 0.0V to 1.0V). I can't remember what the downstream are though. Are you checking them with a scanner with live data or a voltmeter?

Do you have any CEL lean codes? P0171 or P0174? Are both banks showing the same? An easy wat to test if O2 sensors are working is to either unhook a vacuum line (should get lean-out readings) or squirt some carb cleaner into intake tube (should get rich readings.)

If they test okay, then you may a real vacuum leak and O2 sensors are actually reporting correctly. Very easy to blame the O2 sensors and replace them without them actually being the problem. I did this once on a lean code (turned out to be injector stuck closed on a spider 5.7).

 

[Pinger]

Upstreams on average seem to be hanging around half a volt tho I will see them go rich for a few seconds then go lean.

I'm running on LPG and the system adjusts mixture from the O2 sensors. I have a gauge on the dash connected to one of the O2 sensors and once up to temp what I see is what you describe. Mine does swing between the extremes quite a bit - though I could adjust some of that out if I wanted to.

 

[RichLo]

I'm having a problem with a lean stumble just off idle and I've been logging the upstream O2s also. I can see Bank 1 is slightly slower to react than bank 2 but under normal running they produce a jagged sine wave between .1 and.9

And the short term fuel trim follows that sine wave

 

[PlayingWithTBI]

I'm having a problem with a lean stumble just off idle and I've been logging the upstream O2s also.

Are you in Closed Loop coming off idle? A lean stumble could be low fuel pressure.

under normal running they produce a jagged sine wave between .1 and.9

That's good, can you see cross counts on your scanner? FYI here's an example of how a Narrow Band O2 (orange line) should act as apposed to a Wide Band O2 (purple line).

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[stutaeng]

Case #1: Lean codes on BOTH banks is almost always going to be fuel delivery problems. And the logic is that both banks are fed from the same fuel line, so low fuel pressure will affect both banks.

Case #2: Lean on Bank 1 OR Bank 2 (but not both) can be injector problems or vacuum leaks.

For Case #2, if the fuel trims get better with increase in RPM, then suspect vacuum leak. If fuel trims stay bad with increase in RPM, then suspect injectors.

The unmetered air from vacuum leak will be a larger percentage of the total CFM the engine is using at idle. At high RPM, this percentage is lower because the CFM the engine is using is higher, yet the vacuum leak (hole in a hose, gap in intake manifold gasket, etc.) is constant.

 

[RichLo]

Are you in Closed Loop coming off idle? A lean stumble could be low fuel pressure.


That's good, can you see cross counts on your scanner? FYI here's an example of how a Narrow Band O2 (orange line) should act as apposed to a Wide Band O2 (purple line).

Its worse in closed loop but still visible on the O2s in open loop but not noticeable to the driver. And yea my o2s are both reading that high sine wave but just much 'choppier' if that makes sense.

Case #1: Lean codes on BOTH banks is almost always going to be fuel delivery problems. And the logic is that both banks are fed from the same fuel line, so low fuel pressure will affect both banks.

Case #2: Lean on Bank 1 OR Bank 2 (but not both) can be injector problems or vacuum leaks.

For Case #2, if the fuel trims get better with increase in RPM, then suspect vacuum leak. If fuel trims stay bad with increase in RPM, then suspect injectors.

The unmetered air from vacuum leak will be a larger percentage of the total CFM the engine is using at idle. At high RPM, this percentage is lower because the CFM the engine is using is higher, yet the vacuum leak (hole in a hose, gap in intake manifold gasket, etc.) is constant.

Definitely Case #1, both O2s are reading the lean condition but one bank seems to lag over the other.

So both of you think it could be a fuel pressure problem. It has a brand new fuel tank, new pump and new filter just before I acquired the truck. I checked fuel pressure before and it looked ok but I'll check it again tonight. How much variation should I see or not see?

This problem is only noticeable to the driver in closed loop, just off idle and only after idling for approx. 10 seconds or more. Any other time, the truck runs fantastic... tons of power at WOT, idles great, starts great, etc.

Thanks!!!

Edit: Is there anything else I should try logging and watch out for?? I have an OBDLink MX+ connected to an Ipad mounted on the dash so I can see a bunch of info graphed as it happens.

 

[stutaeng]

Its worse in closed loop but still visible on the O2s in open loop but not noticeable to the driver. And yea my o2s are both reading that high sine wave but just much 'choppier' if that makes sense.



Definitely Case #1, both O2s are reading the lean condition but one bank seems to lag over the other.

So both of you think it could be a fuel pressure problem. It has a brand new fuel tank, new pump and new filter just before I acquired the truck. I checked fuel pressure before and it looked ok but I'll check it again tonight. How much variation should I see or not see?

This problem is only noticeable to the driver in closed loop, just off idle and only after idling for approx. 10 seconds or more. Any other time, the truck runs fantastic... tons of power at WOT, idles great, starts great, etc.

Thanks!!!

Edit: Is there anything else I should try logging and watch out for?? I have an OBDLink MX+ connected to an Ipad mounted on the dash so I can see a bunch of info graphed as it happens.

You have the 7.4 Vortec, right? I wouldn't worry about it not occurring in open loop, the ECU is not even using O2 data in open loop as it warms up.

See if you can record or screen shot the fuel trims, spark advance, all 4 O2 sensors, and at the same time looking at fuel pressure when it does it. What are your fuel trims anyway?