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

dude, this could definitely be it! makes a lot of sense. i need someone with an Ultragage to report their S1 02 readings to confirm if what i'm seeing is Lambda. i bet you are right.

i have a wideband gauge and it is reading normal but the sensor is behind the first cat right next to the S2 sensor which seems to be reading normal as well.

 

See what they read on a decel fuel cut, if they go well over 1 (like say 2 or 3) your almost certainly seeing the lambda value.

 

If it's any consolation, I had similar mpg readings about 2 months ago and I'm now back up in the 15-16+ range. It dropped from my average of 15.5 (uncorrected for tires) down to about 12 in the matter of 1 tank. I too thought bad o2's. I put in a couple bottles of seafoam in the tank and crankcase, changed the oil, spark plugs and ran about 6 tanks of 93 octane. Right back where I should be now.

 

This,



you can see it clear as day here. B1/2 S1/2's dont even bother looking at those, those are the post cat o2 sensors that just make sure the cats are doing their jobs.

B1/2 S1/2's are live data for AFR displayed in Lambda "λ" 1.000 is stoich (aka 14.7 - tacos target 14.6 but same same). like stated anything below 1 is rich anything above 1 is lean. At cruising speeds at normal throttle you should be seeing right around 1 as you will be in closed loop and the ecu and fuel system is targeting that stoich value. The sensors themselves can read down to .813 λ and up to 1.233 λ (11.8698-18.0018:1 AFR) - Stock tune (speaking an OEM toyota tune - NA or SC - not a piggy back setup), especially for the supercharged setup targets like STUPID rich values. I have seen around 10.6:1 AFR on a stock NA truck under WOT conditions... no wonder why our trucks stock get such shitty MPG's when loaded down n towing.

my off road only *wink* tune targets no more than 12:1 unless knock is seen (stock safety precaution).

 

thanks for posting the pic. i kinda feel like an idiot now because clearly there's a V by S2 and Lambda sign by S1. i was was misinterpreting the data as V for all sensors.

i feel much better now. i bet the shitty gas just tanked my milage and the truck is already working it out. i'm just gonna drive and see the milage (hopefully) go right back up.

 

Even I skipped over it the first go around when i saw the pic.

 

Seems to be because of Toyota's catalyst over temperature protection strategy (although it doesn't make sense to me how adding fuel would make the cats run cooler), from the HP Tuners Thread Page 21:

 

I should correct that post above, it's actually >75deg throttle angle, not 75% throttle opening.

But spot on.

 

The man the myth the legend! PMd ya awhile back but understand life has been busy!