Poor milage after fillup at sketchy station - shot 02 sensors?

Supercharged 2012 with 96,000 miles and need advice with a MPG issue. It could be just a tank of bad gas that needs to be flushed through but I am concerned about other possible issues.

I got 13.8 MPG at the tail end of a long trip of highway driving. I was getting a few MPG better with prior fill-ups on the trip but since filling a nasty station in Redding CA on November 16 there was a noticeable dip in milage. A dumb thing to do, I know. Also, there was a lot of fuel (6 oz.) when I emptied the blowby canister. Typically there's mostly oil with a trace of fuel and much smaller volume.




No CEL and truck drives fine. I swapped the PCV, air filter, cleaned the MAF sensor, and added a bottle of Techron cleaner stuff to the fuel tank. Checked a few of the passenger side plugs and they look ok to me. When pulling plugs I noticed the clamp securing the snorkel from the fender to the air intake was loose so this could be related to low MPG. I also could have just knocked it loose wrestling the air filter housing out of the way to get to the plugs. Plugs are 50,000 into 100,000 lifespan.





Ordinarily I would just keep driving to see if there's improvement to MPG but the 02 sensor readings on my Ultragauge are tripping me out. S2 seems normal (vacillates from .2xx to .8xx) but S1 on both banks only fluctuates from about .9xxV to 1.2xV so super rich. This lines up with fuel in the blowby and shitty MPG so I keep telling myself sensors are working.



So what's the deal here? Just keep driving and see if MPGs go up? Need new upstream 02 sensors? Injector issue? Fuel pump or filter issue? What do you guys think?

 

What are the fuel trims while driving?

 

not sure how to check. do you know what gauge on Ultragauge will show?

edit: got it from the UG PDF. i'll check and report back.

 

iridium plugs on an NA v6... not the best way to go about things but shouldnt cause the issue you are seeing.

Burn that gas tank completely, fill up with top tier 87 and see how things change if any.

 

got a blower. always use 91+ octane.

i've burned through about 2/3 tank and milage creeped up a bit so i'm hoping it will keep improving as sketchy gas is used up or blown through the motor into my friggen blowby or through the cats.

 

ahhh ok makes sense why only pass side plugs checked then, carry on with burning the shit tank completely.

 

So what are the fuel trims, @lawless ? FYI - I learned that bank 2 fuel trims are usually a bit higher due to the design.

 

went for a drive for about 10 miles checking fuel trim.

i heard shorts are supposed to be between +/-3 and that's where it was for the most part. long was pegged at 7.81 and 10.94 for a while, then it dropped to 6.25 and 8.59.

 

That long term is kinda high, should be below 5% usually. High long term trim means it's constantly having to add more fuel to keep the mixture correct. That gas from the crappy station is suspect. Crappy gas won't burn efficiently and combine with oxygen molecules, resulting in leftover oxygen going down the tailpipe. The extra oxygen is noticed by the oxygen sensors and tells the pcm to add more fuel. Trims are your window into that decision making. You were on the right track by looking at oxygen sensor activity, but those numbers jump around rapidly. The trims are better because they condense the oxygen sensor readings into a more "watchable" number. Something you can have on your lap while you drive around..

Run through that tank and then fill it with Supreme from somewhere. See if the long term comes down with the better gas. If they do then the crap gas was the problem.

 

But.. some other supercharged guys might chime in. 8-10% might be normal-ish when you're boosted.

@12TRDTacoma

And when I say trims, I'm talking Long Term. Short term responds to *obviously* short term demands like going up a hill or accelerating off a stoplight. Long Term is the better mpg indicator because it's looking at consumption over a longer period of time.

The real test will be when you get a fresh tank of Supreme and see what the trims do. If Long term goes down you can blame the gas. If it stays up around 8-10% then you have to start looking elsewhere like driving habits (cough.. lead foot.. cough) and mechanical stuff (tires, weight, brakes dragging, etc)

Good luck

 

i was going to post in the SC thread but decided against it because this may not be a boosted-only issue.

thanks for the reply. the tank of presumably crappy fuel was almost empty when i filled up with 18 gal (21 gal tank). Since that 18 gal fill i've added 32 gals in 3 partial fill-ups. the tank is full right now so i've burned about 30 gallons since the bad tank. general gist from the interwebs is that i should burn through 2 or 3 tanks to try an get all problem fuel out. hopefully this will work itself out.

 

Last time I got a bad tank I noticed lack of power around 4K rpm along with weird fuel trims. I added a high quality octane booster and topped off with premium and it went away.

Have you noticed any performance changes?

 

I use Arco cus its cheap and its a name brand, meaning if something happens to my vehicle and others theyll fix it, it aint worth the bad publicity for them, but places like “quik nd serve’, “the last stop” lol all those random no name gas stations I dont bother. I know its tough if thats the only gas station around. gl

 

no issues. just bad MPG and lots of blowby.

after filling with good gas and driving 200 miles i checked the blowby and there was none. this adds support to the theory of bad gas. my poor motor just wouldn't burn that shit. the truck passed it like bad clams.

 

If the bad gas had water in it you may still need to add a bottle of Heat or gas line antifreeze with methanol to trap any remaining water and burn it off.
The 10% ethanol gas does nothing to trap/capture the water. Check your oil fill cap for condensation.

 

were these numbers taken while cruising or at idle? idle does all sorts of weird things, for useable data get up to normal cruising speed and gear and note long term trims.

 

i took shots of idle and while driving. mostly +/- 3 short term while driving. Long changed a few times but was mostly pegged at about 7/11 or 6/9.

no condensation on the cap. i put in a bottle or Chevron fuel treatment after filling up and i just added an octane booster.

 

Once warmed up fully (like 10 min of driving). Long term fuel trims were 6-9% while driving with steady throttle at cruising speed? thats well within tolerance

 

thanks for confirming.

i just can't explain the hi voltage readings on the upstream 02 sensors. maybe i need to drive a few more thanks through and the V will go down and MPG up. i hope so.

 

The upstream sensors are wideband sensors, they operate differently than a conventional O2 sensor.
Your ultragauge is likely displaying the Lambda value (1 is stoichiometric anything above 1 is lean anything below 1 is rich) for the sensor instead of the actual voltage which itself is a calculated value.