Seems lately my AFR's have been bouncing around alot .... Maybe i didn't notice it before but I'm almost positive they were pretty steady around 14.6 cruising and 12.6 WOT . I'll be idleing around town in 3rd at 0 boost and see 13's that jump to 15 and back to 14's ...... could this be the o2 sensor starting to take a ****?

If the o2 is going is it possible to switch the primary and secondary o2 to test it out? I'm catless so it wouldn't be a big deal to switch them over for a few days ...... thanks.

 

at idle my AFR will bounce around anywhere from the upper 13's - 15ish. i wouldnt really worry about it IMO

 

I tuned my idle today and it sits right at 14.9 - 14.3. Also your air fuel is at 12.6 wot you are 1 point to high. It should be more like 11.7

 

he is an LNF. another beauty of direct injection. go lean

 

The only time that you will see your AFR numbers solid will be when you first start your car and when you are at WOT.

 

Don't the primary and secondary O2s run in a different range?

 

I just checked and GM lists different part numbers for the front and back so they are different . I've seen people do this with other cars so i thought it might be a possibility ....guess not

 

the front o2 sensor on your car is a wideband so you can not switch them. either way your AFR is always going to be fluctuating at idle. really what the engine is doing is switching from rich to lean around stoich 10 times per second. the wideband won't see it that closely but there will be some fluctuation at idle/cruising AFR's

 

Sounds like the Front O2 is failing..

 

Thats what i'm thinking ...... in cruise mode I saw it go from 14.7-8 to 12.7 without any throttle input or load difference on the engine . I know some fluctuation is normal as ive see low 14's to mid 15's before ....but now it's diping into the 12's and 13's for no apparent reason . It's fine at WOT from what i've seen , hold 12.6 .

This started happening after i did a NLS to 3rd last week . After that everytime i would get on the throttle the timming would show -1 threw -5 and time past 1/2 throttle . I shut the car off and flashed the stock tune back and it still ran hardly any timing . I let it sit a few hours .... reflashed the Superchips tune and cleaned the maf and checked the plugs ..... the timming has been normal ever since showing up to 11-12 degrees at the top of 3rd.

I'm thinking the NLS caused a misfire and put the car into protection mode .... but whats weird is no cel's came on ... and It would still boost 20psi but pull all the timing out . I only did that once just to check cause i didn't want to hurt the car any worse incase it broke something .

All seems fine now except the AFR fluctuation. Sry for the essay .... thanks for any help.

 

ALSO,

Check for slight boost leaks. Maybe you popped a charge pipe loose when you NLS or something stupid like that. An air leak would explain fluctuation.

What are your LTFT/STFTs doing?

 

Another thing is try unplugging that purge solenoid on the front of the intake manifold and see if that cures it.

But Im better Front o2, that's what my car is doing again and its the same as the last time it went bad! $60 from GMparts! not too bad

 

I did check all the charge pipes and got a turn or so on the intercooler endtanks . My trims are staying right were they have been with small variations in the weather. They had jumper to minus 7 the other day so i went back to the stock filter and put the vacuum tank back in the system .... they have been -3 ever since. Vacuum readings on the boost gauge has stayed right on -20 like it has since new .

I ordered a new set of stock plugs yesterday so hopefully they will help. I've seafoamed my car a couple times in the last 5K miles so I'm hoping i didn't gum up the o2 with the **** it cleaned out . The plugs looked decent when i pulled them except they had some black liquid on the threads .... not really oil consistancy ...it was a lighter liquid then that .... but looking at the pistons and the plug ends they are dry with some black carbon on the end of the plugs. I was running a .032 gap and opened it up to .035 and have noticed a lot less snap crackle pop when deceleration ....weird.

Thanks for the suggestions !

Thanks BYT .... I'll try it . On a side note i have my superchips tuner sold so I'll be in touch about a Hp tune file . Thanks

 

He is not an LSJ. My car runs 13.0 A/F at WOT has for 22K miles now.

 

There is something else i've been wondering ..... I have seen positive fuel trim's 1 time only in the life of my car ...... and i've ran the ZZP airbox mod with the snorkel cut and pointing straight down .... K&N drop in ....and with the snorkel removed to leave the bottom of the air box open.

Now in my way of thinking that should allow more air into the system but yet the car is pulling fuel with the trims cause it thinks it rich?? I also have a cattless DP which should free up some flow as well . Any thought's on this? I know rich is better than lean but if i've opened the air ways so why does the car act like it's not seeing enough air? thanks

 

Modding the snorkel and/or adding a K&N drop in filter causes the MAF to "see" more air than is actually entering it. The WB 02 sensor detects that the A/F is richer than commanded and tells the ECM to shorten injector pulse width to compensate. Certain intakes will cause negative fuel trims others like Hahn's will cause very positive fuel trims. Depending on a lot of factors including intake diameter, MAF position on the intake, MAF location with respect to the filter. What kind of filter used, etc.

 

Thank you for the response . Whats weird is even when it's back to bone stock ( I bought a new snorkel ) I still haven't seen + trims which i guess isn't a big deal but made me more curious than anything else.

Could it be with the Catless DP install that i freed up the back end allowing the wideband to see air pass by quicker than when those 2 cats were holding it up some?

 

To understand the MAF's role in fuel trims think of this exaggerated example:

Pretend that the pipe going into the intake was really big... like a couple feet wide. And the MAF was sticking through the pipe and coming out of the left side of the pipe.

Now if you've got a fan, and hold it up and blow air through the pipe, the MAF would detect the flow. If you pointed the fan to the right side of the pipe, the MAF would detect maybe some flow but some of the air is getting past without getting read correctly (and would result in positive fuel trim). Now if you pointed the fan at the left side of the pipe and blew the air right on the MAF, the MAF would read a lot of air, but since it thinks that that much air is flowing through the whole pipe, it overestimates the air going in and the ECU needs to correct (negative fuel trim).

Sometimes irregularities happen inside the pipe, and the airflow may not be uniform inside the pipe (why putting the MAF along a long, straight section of pipe is a good thing). For instance, maybe more air is hitting one side on the inside than the other as it goes into the pipe.

Total airflow and fuel trims are two related yet different things. You can have a lot more airflow and still have a zeroed fuel trim.

 

Good analogy.

 

i just picked up my car yesterday and after a NLS getting on the highway this morning it pulls all the timing between 3-4k and runs like total dog crap but hasnt thrown a code... once you get above 4k it pulls just fine and still makes 15.xlbs of boost... runs okay below 3k and above 4k... a/f seems lean as anything to me tho using the built in wideband... then again i had an AEM gauge type UEGO in my mustang with conventional injection...

sorry to hijack the thread but... yeah...

 

Let me guess ...... you have less than 1500 miles on the car? They all do that till they get some miles on them .....mine was terrible when it was new . These DI engines run alot leaner ... I see 12.6 @ WOT.

 

Mine would pull a ton of timing for the first month. It really freaked me out

 

Did anyone figure this out.... My car is pulling alot of timing, and it even went into -5.5 degrees of timing.

 

At full throttle? I see negative timing after starting the car during the cat warmup period.

 

whats the part # for the front 02 sensor?