How did you calculate your MPG's?
Are you starting from a full tank then refueling near empty and using gallons pumped or are you still going by the needle and miles driven?
Have to ask.
City/Hwy percentage?
I agree that's low, but it's so low it would point to a problem elsewhere.
Do you have a torque app/ bluetooth adapter?
You must check everything..
Did you get all the vacuum hoses reattached?
Does it feel like its lost power...are the plugs fully seated?
I don't know if it's possible to get the wrong O2 sensor in the wrong hole...but something to verify.
If it's the first tank after all the work, with a fresh PCM relalearn, I would wait another tank.
I am doing all city driving and I expect to get at least get 14MPG
I haven't gotten the Torque tools yet, I was waiting to see how the MPG was after a while
All vacuum hoses are attached and look fine, I will be getting the Ac Delco gas cap tomorrow as the seal ring appeared to have cracks in it on my old one, after I checked it from a P0440 code that popped up again
No power loss and plugs are fully seated its running super smooth, better then when I first got it
Not possible as upstream and downstream have different plugs
What's your driving style, driving Miss Daisy or Talladega nights?
Fuel is going somewhere...
Leaking/evaporating
Heavy foot
Unmetered air
Weak engine/low cylinder pressure.
The torque app is very useful in watching knock retard, ignition timing, O2 sensor function, and fuel trims.
When you get Torque up and running we can narrow it down further.
Sorry if I missed this, but did you get an exhaust back pressure test done?
He wants to know if you added a lift kit to bring the suspension higher than stock.
I can tell you that I gained 2 MPG with a new O2 sensor as I suspect that my old one was getting lazy. Reset the PCM and bam! 14MPG (EXT with 3.42 gears)
If you want a nice long read, this was the mother of all MPG loss hunting threads ever, all 12 pages.
Only getting 160 miles on 25gal tank
I think he also had a little bit of a heavy foot as well.
Something else to check is the fuel pressure regulator. I replaced mine less than a year ago and it smoothed things out a little....something worth trying because you can't verify pressure after the regulator so it's not throwing money into the wind.
I am doing all city driving and I expect to get at least get 14MPG
I think I averaged about 14 MPG in the Envoy with mostly city/traffic driving even with two-hour easy highway trips per tank. So, to expect 14MPG with all-city driving doesn't seem guaranteed. That's why I had no hesitations switching to a Suburban because city MPG won't be much worse. Try doing some easy highway driving at 65 (I lost MPG because I was hauling ass at ~75). 20MPG is doable on the highway at 65. Been there done that. But going too fast on the highway or in the city these things are still heavy, body-on-frame, somewhat brick-shaped SUVs. I'd look back at my Fuelly but I got annoyed and deleted it for my Envoy.
There are many factors that can contribute to a loss in MPG, you need a healthy engine though so without driving it, seeing it, it's hard to pin it down which is why we ask a bunch of questions and I appreciate your feedback.
I will always ask to check the vacuum, make sure your intake manifold bolts are tight, still doesn't rule out a gasket leak but it's a start. without seeing results from a torque app, there's always the chance of carbon knock in which you will likely not hear.
The fuel pressure regulator again is one of those things that can contribute to issues with fuel atomization and you won't know it's bad because you cannot verify pressure aft of the regulator. You aren't throwing money away if you change it and I would recommend changing it with about 150K on the clock. That's not a rule of thumb, just preventative maintenance. You could have puddling fuel and not know it, requiring more fuel to complete the burn as you wouldn't have fully atomized fuel to use.
You can do a load test by placing a board against the gas pedal and the seat, holding the RPM's to about 1500 and pull one coil pack at a time, noting the RPM drop...all cylinders should be pretty close, a weak cylinder would show less of a drop and would be obvious...not sure of the exact tolerance, maybe 10% but not sure....don't quote me.
What tires are you using? Low rolling resistance tires will get you a couple MPG's..this is not a fallacy.
It's not so much the weight of the tire, but the entire composition. ..ie, carcass, sidewall, tread design, etc. I lost 3 mpg's once to a set of Kumhos, I sold them with 50%tread to cut my losses, not agressive by any means.
What pressures are you running? I always keep mine at 35 psi cold, 33 or under I notice a loss in MPG's
Check the sidewall of the tires, max pressure should be prob 44 psi...granted this is for increased loads but it's a good indicator you can run 35 all the time...most tires are this way.
I'm pretty sure you didn't lose 4 mpg over tire pressure, but low pressure will absolutely affect MPG's.
Get a good gauge, don't eyeball it, and in the morning if you're parked outside, check the pressure before the sun hits the side of the tire. Sunlight will increase pressure quickly as black is very absorbant of sun radiation.
Report back what the pressure is, if you're at about 28-29 psi, you can bet your mpg's will drop off a few compared to 35.
Low pressure will wear the inside of the tire. Yours could be the result of worn suspension.
Since this is a MPG thread, you do need to verify all these factors or its a lost cause.
Copy.
Just another base to cover.... definitely interested in seeing the fuel trims.
No clue what those components fail are but are likely related to your P0440.
Just looking at your fuel trims, they seem to be off a bit but, in the first set of pics, less than the 10% that usually means trouble. Negative trims means it's running rich and it's cutting that much on fuel to compensate.
In your second set of pics, your LTFT is off by over -10% (-11.72%) which means it's either getting too much fuel or not enough air. Could be cause by the evap system dumping too much fumes into the intake. Could also be caused by a dirty air filter.
If you want more info on fuel trims, this video explains it well despite the robotic voice.
I'd say track down and fix your P0440 before doing anything else.