I have an 07 trailblazer with an Lh6 in it. Couple of months ago it developed an intake leak that was causing a pretty bad misfire. Got that fixed, and while I had the intake off I figured I would also do the o2 sensors, since they had almost 200k on them.

Now, I have a random, inconsistent misfire at idle. Not super significant, but enough that I know somethings up. My MPGs have also taken a huge dive. Before I was averaging around 18, now I'm down to 14 after a solid month of regular driving. The new o2s i put in were a pair of Bosch's i got off of rockauto.

Im thinking either it's developed a new problem somewhere, or these o2s are calibrated wrong and are making the car think it's lean when it's actually at stoich? Does that even make sense? Also, no codes.

as soon as my new laptop comes in I'm going to log the data and see if that shows anything anywhere as well.

 

GM computers do not like aftermarket sensors. get a set of GM/AC Delco sensors for it and see what happens.

 

I've had no problems with the Bosch ones O'Rielly's sells.

 

I’d say the O2 sensors are probably a major suspect here. If you can, maybe try swapping them for something like Denso or another trusted OEM equivalent and see if that improves things.

 

Ok, use your nose after the engine is warm.
Measure black and gray wires with a voltmeter.
The reading at Stoic is .5 Volts

 

Which cylinder(s)are misfiring?
Are there any DTC's?
What does the misfire history look like?
What are your STFT and LTFT?

 

Bosch invented the O2 sensor as we know it, holds the patent (or at least did, don't know the expiration date), and licenses it to other mfrs.

"GM" buys O2 sensors from whoever makes them cheeeeeepest. More often than not, for GM, that's Delphi, the current name of the former GM division producing such products that was spun off in the late 90s. Not always though. Replacement ones are even more vague: any branded box might contain any other mfr's product, for any given application. Makes more sense for mfrs to buy each others' products to sell at parts stores, than for every single mfr to "make" every single possible variation that they might want to supply.

In my experience any O2 sensor from any of the OEM grade mfrs (Delphi, Bosch, Denso, etc.) is pretty much interchangeable. It's a simple chemical process that they work off of, the same in ALL of them. No "magic" goes on in any mfr's plants. Nothing about them is materially different from one to another. The castings and sheet metal do not care who made the sensors or vice-versa. Nor do ECMs. Nor does fuel.

Idle problems in a MAF system are usually caused by leeeeeeeks in the intake system behind the MAF. Usual symptoms are exactly as you describe; random misfiring esp in gear and esp when the engine idles that way for a long time and esp if it kinda gets worse as time goes on (think, the drive-thru window). I'd look there first. Intake manifold gaskets in particular. A data log during this condition, compared to one when the intake is not compromised, will usually show low MAF readings from the ECM closing the throttles to maintain correct idle speed in spite of the extra air coming from somewhere besides the throttle body, low throttle position values also due to the above, and lean mixture (which is what actually causes the misfiring) due to lack of fuel being added for the unmetered (unknown to the ECM) air.

 

OK RBO = BAD TECH
The first EGO (one wire) was created for Hitler, used for stoch measurement in a STEEL Furnace
SURE, Bosche manufactured that item under German (NO Patent) law.
I found the ONE WIRE EGO would read incorrectly due to the exhaust system resistance.
THUS, I worked with NTK AND created the TWO wire EGO.
Later, due to USA COULD START laws, we created the FOUR wire "heated" EGO.
Lance

 

https://en.wikipedia.org/wiki/Oxygen_sensor

"the O2 sensor as we know it"

Wouldn't surprise me a bit though, that there were predecessors; probably ALOT more than one; after all, it's a pretty common kind of thing to need to know, across many fields.

 

The EGO Nerrst cell is a BEYYER read.
What I state is NIST certified (the Truth)
Your WANDAPEEKA read is lacking history, accuracy, and TRUTH
Lance