2009 Accord V6 terrible MPG

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309
Location
Rainville, USA
Evening BITOG My 09 Accord is drinking fuel like a large SUV, it has 29k miles and has been averaging about 17mpg in mixed driving lately. I just did the brakes, front and rear, and the calipers are not dragging anywhere, new air filter, tire pressure 33psi all around, ran a tank of techron through it but can't get to the bottom of it. It runs great so I'm not sure what to try next to get the mileage back. I also tried unplugging the battery for 30 min to reset it. What say the smartest forum on the internet?
 
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12,584
Location
Phoenix, AZ
Depends on what you mean by mixed driving. Need some details, what's a daily commute look like, how many miles highway and how many city? Stop and go traffic? Any idling to warm up the car?
 

JEL01

Thread starter
Messages
309
Location
Rainville, USA
Sorry was distracted by the MNF game. My commute is about 8 miles each way with 3 in town and 5 on the highway and some 20+ mile open road drives thrown in there regularly. I don't warm it up at all either. I'm thinking maybe cleaning the TB and MAF is in order, also nothing fancy in the crankcase, VWB 5w20 and Honda filter (oil and air) 700 miles ago
 
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JEL01

Thread starter
Messages
309
Location
Rainville, USA
Originally Posted by ctechbob
Is this something new that just started?
Yeah over the last few months, not sure what's going on, no CEL/codes
 

JEL01

Thread starter
Messages
309
Location
Rainville, USA
Nope you read that right, 29k. I got it a few months ago from a relative who rarely drove it, but it had been well cared for and perfectly fine until a couple months back. I have a VCM killer (SVCM) ready to install, but I want to get the baseline MPGs back before going that route
 
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920
Location
D/FW Metroplex
Such a short commute could be preventing closed loop operation of fuel/air mixing. Open loop isn't going to be fuel efficient, isn't supposed to be. If the car never reaches closed loop, or it is only there for a short while, less than expected MPGs would be the norm
 
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1,466
Location
Maryland USA
By any chance do you drive with one foot on the gas, and the other on the brake ? If you have a IR thermostat , try reading the temps of the wheels and brakes- to see if you have a binding brake.
 
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1,906
Location
Canada
29k over 10 years tells me that most operation is very short trip. I know the mid 2000s Hondas (I-4 K24 and the V6's on the 7th gen) were incredibly aggressive at running very rich after startup to light the cats ASAP -- the 9th gen moved to DI and an exhaust manifold mounted cat to resolve such. Get a scan tool on it, make sure its coming up to temperature (190degF or higher) to rule out a stuck open thermostat, but unless its throwing codes, or has drivability issues, the root cause may very well be just very short trips. As others have suggested, put it on jackstands, put into neutral, and spin the wheels to detect dragging brakes.
 
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12,890
Location
ROCHESTER, NY
In the Altima 2.5 in my signature, I just put on my winter tires/wheels and filled up the gas tank. I'm now getting 21 mpg, down from 29 mpg. AND I just freed up the driver side rear brake. I think it's more to do with the tires in my case and the temps just hit down into the 20*F over night.
 
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2,879
Location
Malaysia
I'had similar issue of fuel consumption increase up to 20 % despite 44 psi tire pressure vs 31/35 at pillar . Check and replace O2 sensor , back to normal .
 
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16,717
Location
NH
Originally Posted by JEL01
Nope you read that right, 29k. I got it a few months ago from a relative who rarely drove it, but it had been well cared for and perfectly fine until a couple months back. I have a VCM killer (SVCM) ready to install, but I want to get the baseline MPGs back before going that route
I'm a little confused, you indicated that it used to get better mpg, but now you indicate you are still trying to get a baseline. If it's new to you, and being used on short trips, then perhaps this is baseline. Have you taken it out for a nice hour long plus highway drive? Maybe it does great out on the open road, which would indicate no problem. OTOH maybe you've got a bum thermostat.
 
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12,584
Location
Phoenix, AZ
Originally Posted by pitzel
29k over 10 years tells me that most operation is very short trip. I know the mid 2000s Hondas (I-4 K24 and the V6's on the 7th gen) were incredibly aggressive at running very rich after startup to light the cats ASAP -- the 9th gen moved to DI and an exhaust manifold mounted cat to resolve such. Get a scan tool on it, make sure its coming up to temperature (190degF or higher) to rule out a stuck open thermostat, but unless its throwing codes, or has drivability issues, the root cause may very well be just very short trips. As others have suggested, put it on jackstands, put into neutral, and spin the wheels to detect dragging brakes.
I agree with the thermostat, gauge can show a general temp but in reality it might not be up to temperature. But I wouldn't expect this thing to be a gas sipper.
 
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2,529
Location
wv
Originally Posted by JEL01
Sorry was distracted by the MNF game. My commute is about 8 miles each way with 3 in town and 5 on the highway and some 20+ mile open road drives thrown in there regularly. I don't warm it up at all either. I'm thinking maybe cleaning the TB and MAF is in order, also nothing fancy in the crankcase, VWB 5w20 and Honda filter (oil and air) 700 miles ago
Ok the obvious.. What you are describing is Severe Service. Your engine and drivetrain rarely get to reach its most fuel efficient temperature. In my opinion the mpg you are seeing is fair. However with a 10 year old vehicle with 29K miles, there could be critter nests in the exhaust or intake.. I think an italian tuneup and a highway test thereafter on mpg would yield much better results.
 
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1,707
Location
British Columbia, Canada
In your introduction you say you're having problems with an '09 Accord V6. In your signature line you say you maintain an '05 Accord V6. Did you have a slip of your typing fingers? Is it the same car? Different series, potentially different problems.
 
Messages
640
Location
Colorado
OBDII on-board diagnostics are usually very good at flagging rich mixtures (bad MPG) via the oxygen sensors. I like the "open-loop excessive" theory above which would indicate the thermostat may be too cold possibly. Maybe the wrong one was put on in the past. Side note: Fuelly.com has a 2 million mile average on '09 3.5L V6 Accords as 22.0 MPG, so 17 MPG may not be that far off anyway with short trips. Its a drinker by design, as current new Accords average closer to 25+ MPG.
 
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