Running rich

Good article that explains a little more in depth. The voltage reading your getting is telling the computer it's lean. http://www.import-car.com/troubleshooting-wideband-o2-sensors/

 

100% positive that is the value. when cold it typically starts out at 3.3ish (which is what i understand to be normal) and climbs to 4.991 as it warms up and stays there

 

It's sensing its lean.

 

but it's not.

the article you referenced seems to be pretty detailed and thourough. i'll reread it and see if it points me in a particular direction. right now it seems as though my AF sensor may be bad? or at least maybe a bad heater circuit?

 

Right it's not.

 

The heater circuit doesn't affect the tune once it's warmed up well FWIW. Seems an awful lot like a bad sensor. The engine has good vacuum (you said -20in/hg), there's aren't any very vacuum obvious leaks, and you'd definitely notice a leak at +40 LTFT. Your exhaust manfold doesn't have a crack, again that would be pretty obvious from the noise.

It's GOT to be a sensor, or maybe, just maybeeeeeeee the ECU but I seriously doubt it. Some sensor is my vote. AFR o2 or MAF or TPS

 

from what i've read, the AF sensor needs to be at a temp of 1200* to operate correctly. if the heater circuit is not not working as it should and the sensor does not get to 1200* what would the symptoms be? it must need to be at that temp for some reason.

i am seriously racking my brain trying to remember if we had poor fuel consumption/running rich before we changed the AF sensor back in November. i seem to recall that we did and if so, i would really find it hard to believe that the new sensor has the same issue as the old (not that it is impossible). which has me leaning toward the heater circuit.

MAF sensor is recently replaced and my scanner indicates it is functioning (although i have not verified the values are what i would expect to see at various cruising speeds)

the TPS sensor also appears to functioning as it should. at least the values change in a positive direction when pressing the accelerator pedal and back down when released (again have not verified actual values with what they should be)

i can't seem to get away from the thought that it's something faulty with the AF sensor or circuitry. if it is sensing lean, everything else is doing what it is supposed to. ie... the ecm is adding more fuel (verified by the LTFT).

the problem is the AF is reading "lean" when it is actually "rich". that fact pretty much rules out all other components (at least fuel related components like filter, injectors, pump) being faulty doesn't it?

heck, i would even think i could rule out a vacuum leak without even looking for one. if i had a vacuum leak and i was running lean i could see throwing a "lean code" but it would truly be "lean" wouldn't it?

 

At this point, it's worth it just to change the AF sensor again, IMO. Buy it at a local part store so you can (hopefully) return it if it isn't the solution.

 

If I'm not mistaken, every gas engine since the 80's has an EGR valve. As a matter of fact, I think every engine since somewhere in the 70's has an EGR valve.

 

i ordered a new Denso AF sensor and confirmed that they will take it on return if it doesn't solve my problem. if it doesn't then i will have to dig into that heater circuit to verify it is operating as it should

 

well guys, here's the latest: GOOD NEWS !!!

installed the new

$146 Denso 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

Denso 234-9001 AF sensor and all is good....so far!

installed it and immediately began monitoring the readings. AF sensor immediately gave "different" readings than i previously observed. as it warmed the readings changed slightly but didn't just climb to 4.991 like previously. i could blip the throttle and see the numbers climb/drop then settle back to a decent reading around 3.2-3.3 ish.

i then disconnected the battery for 10 mins to allow the LTFT to reset to 0. drove about 10 miles before i saw a value appear and again it was a reading more in line with what i would expect (not 39.xx).

also observed that the STFT was a value different (lower) than before.

most importantly the idle smoothed out and during a drive with varying cruising speeds (35-60) it also ran much smoother!

after about 25 miles of driving....NO CEL !! (it was previously returning almost immediately)

so in conclusion either the

$147 Denso 234-9002 Air Fuel Ratio Sensor

Denso 234-9002 that i installed back in November was faulty or it is calibrated differently than the 234-9001 that my vehicle calls for

hopefully the fuel mileage will improve significantly now. we'll put some more miles on it over the next week and i'll report back the results

 

any further updates on your fuel mileage and long term results? i have been chasing extremely similar issue but don't have to tools to read and get the numbers your seeing but everything else you describe or have done to test it i have also done with vary similar results.