For the past year i havent been able to figure out the cause of my horrible mpg
just for reference with extreme conservative driving (manually shifting each gear as early as possible) im lucky to get 15 maybe 16 mpg in stop and go traffic in the city
with extreme conservative driving on the freeway, i can achieve 28 mpg which is just around what this car is supposed to get

the problem is if i drive 80% freeway and 20% city my overall MPG for the 17 gallons ends up between 19-20 mpg... Basically im getting 280 miles a full tank when the light turns on... i used to get 24-26(mpg) 350 miles EASY without even trying... this is with the same driving route and same driving habits

about 10 months i had a CEL pop and it was either P0174 (System Too Rich Bank 2) or P0172 (System Too Rich Bank 1)
can remember which one it was i have to check my paperwork but i was getting rough idles from a cold start and sometimes delayed acceleration and my idle would bog down below 800... i took my car to a shop and they decided i needed a valve adjustment
several hundred dollars later and 4 revisits to the shop and another valve adjustment the shop did on the house
the car is still running rich... car doesnt bog down anymore but i still get very bad shakes on cold startups (goes away once the engine warms up)



Looking at my Short Term Fuel Trim for bank 1 and 2... its jumping all over the place
I took this picture after a 20 mile home from work and pulled into the garage and put the car in park just idling

If you look at the STFT gauges (bottom right 2) during idle it was Positive 12.5 in bank 1 and Positive 5.5 in bank 2
but my bank 2 still pulls ALOT of fuel at times randomly for a few seconds at a time when i let off the gas while driving...
you can see under bank 2 STFT's lowest value was -22.7%.... im wondering what the hell could make my fuel trim doing this

ive already gotten 2 valve adjustments, last one being about 5 months ago
leaking fuel injector?
ive replaced the PCV valve with a brand new oem one 2 months ago

i went to another shop that specializes in hondas and acuras and when i have time i will be dropping it off
but he already said it mostly likely isnt a vacuum leak because there arent any lines specifically going to bank 2


can anyone give some insight or input some ideas on what it could be? thanks in advice

 

Oxygen sensors? Spark plugs? Is the only thing you have done is the valve adjustment?

 

spark plugs were replaced 40k miles ago... havent replaced the o2 sensors yet, but dont the o2 sensors usually pull a code if they go bad?

 

Did you replace the spark plugs with OEM ones?

 

o2 sensors DO GET LAZY over time.
so, might not be at the threshold of being bad, but still letting wrong a/f mixture going through
just food for thought

 

You are going through a full 17 gallons every time? I am ignoring the 2nd half of your post since I am clueless on that part. The first half though...sounds pretty normal to me. What is your actual AVG MPH and MPG from the MID? Getting sub-20 in true stop and go city traffic and high 20s on the highway sounds about right. My '05 averages out around 21 most of the time when I am driving since there is very little highway, while on road trips we get around 28-32 depending on speed. In true mixed driving, it is usually around the 25-27....again really depending on what the average MPH is.

 

They were replaced with either denso or ngk, pretty sure it wasnt oem

i just order a NTK o2 Sensor for the Upstream for bank 2.. should arrive on 22nd

So basically what i do every time i fill up the entire tank is reset the MID and let it run through til the gas light comes on. I cant remember what the exact AVE MPH is but its usually somewhere around mid 30s to high 30s. ill record my latest one and report back.
sub 20s in the city and high 20s on the freeway is completely normal. However keep in mind this was with EXTREME conservative driving. Meaning i was shifting into 4th gear by the time i hit 30mph and 5th gear by the time i hit 40mph. If i drive under normal driving conditions (eg. shifting around 3k - 3.5k) my city MPG drops to around 13-14mpg and my freeway drops to around 23-24mph and i end up with a AVG MPG of 19 (20-30% city driving / 60-70% freeway)... i used to easily get around 17-18 mpg in the city and 25-27 mpg on the freeway driving normally and 320-350 miles on a full tank
now ill be lucky if i can get close to 300 before the light comes on... more like 280ish on a full tank with more than 70% highway miles..

ive had CEL P0172/0174 (which ever one it was) pop 2 or 3 times early this year around march-may... it was dumping more fuel than it was supposed to making it run rich. i havent had the code pop on me since may but the mpg is still suffering and my fuel trim is showing evidence that its randomly dumping fuel a few seconds at a time

 

NGK Iridium is good


Denso = no good.. pop off the coil and have a look see!

 

Just a guess but check your cats. I had to do the 04 TL to 07 Honda transmission swap. My car had also been throwing O2 errors randomly. Not often though. Anyway, having dropped the exhaust to get to the transmission, I noticed garbage rattling around. I cut the pipe and a crap load of material had come loose from the front cats and was partially blocking the rear cat. Eliminated the rear cat.
I'm getting 27 MPG average now! I drive around 70% highway.

 

ill have to do that this weekend when i have time, thanks for the input

i believe we have 3 cats on the TL right... 2 precats up top and 1 down by the j pipe... i could probably pop the bottom one off and shine a flashlight in it to and do a quick visual inspection but the top 2 cats would take some more time, especially bank 1

 

okay so i have a quick 30 second clip of my car on a cold start up idling and accelerating then coasting to a stop sign
you'll notice at idle Bank 2 is already pulling fuel (-10%) while bank 1 is within normal range (1.6%) a perfect engine in theory would have both banks at 0% during idle... so you can see there is definitely something that is causing me to run rich which is causing my poor mpg


once i accelerate bank 1 does what its supposed to do, which is pull more air, while bank 2 is barely pulling air
lastly once i left off the pedal and coast you see instantly bank 2 pulls WAY more fuel than it has to (-21%)... i believe this is one of the reasons why my city MPG is so horrible its constantly pulling fuel in stop and go traffic.... while freeway driving i can avg up to 27-28 because either banks rarely pull as much fuel while im on the freeway... on the freeway the gauges are much more calm and is usually within + or - 5% on either banks

 

anyone have any thoughts or input?

 

id think the injectors on that bank would be the culprit. Seems like if the cats were messed up both banks would be acting funny. And if bank 1 is acting normal, it cant be anything with the intake system as that would affect both banks as well. No codes leaves me to think injectors that arr still functioning, just not well. Might be time to do all of them.

 

i was thinking it could be a leaky injector in bank 2, i just wish there was some way to test it before i pull the trigger on a set. i was thinking of maybe swapping the 3 injectors from bank 1 over to bank 2 and see what that would do to my fuel trim

 

Issue is in only a single bank, so what is unique to each?
- Valves
- Injectors
- Coils/Plugs
- Pre-Cat
- O2 Sensor

Valves
You state you have already had these adjusted and should be out of scope for this discussion
Injectors
This is a big unknown, but a leaky injector wouldn't cause the computer to dump extra fuel into the bank..a leaky injector would already be doing that for you. The computer should register a rich condition and pull fuel. If I am reading your post correctly, you are seeing that the computer keeps increasing fuel to that bank right?
Coils/Plugs
Have you pulled the plugs to take a look at them? See if they are drenched in fuel, discolored, or anything else that may clue us into if it is a single cylinder issue or something bigger.
Pre-Cat
The fact that it runs fine on the highway makes me want to ignore this....for now. In theory, if it were plugged it wouldn't run well especially at higher RPMs.
O2 Sensor
This is what I would be looking at next after the plugs. A wonky sensor can make the computer do all kinds of odd things. It may still be within the voltage specs, but it doesn't mean it correctly sensing the current state.

This is my theory at this time being the experienced keyboard Internet mechanic that I am.

 

Do you have the hand break on? haha just kidding

 

my NTK o2 Sensor upstream is supposed to arrive tomorrow, ill get it switched out and reset the ecu and report back... fingers crossed

i wish it was that simple haha

 

That would definitely tell you if its one of those injectors. If the condition does't move, then it might be a sensor. Hopefully not an ecu issue.

 

Just came across this thread and I have the same issue on my TL. Did you ever get this issue fixed, and if so what did you do to fix it? Thanks.

 

I know this is an old thread but I’m having the same issues
did you ever fix your issue? Was it the O2 sensors? Thxs