djcrunkmix

Hi guys,

I am just really frustrated that I somehow cannot improve my bad gas mileage. I have a 2001 Honda Accord EX V6 with 132K miles on it. I used to be able to get the rated gas mileage (20/28 - City/Highway) when I bought it at 90K miles on it. Somehow, from last year or so, my mileage has been deteriorating (I only get 18/24 now) and I did every bloody thing that I could as follows:

1) Replaced the spark plugs
2) Checked tire pressure
3) Flushed the rad when the engine coolant temperature sensor went bad and replace it as well.
4) Switched to synthetic oil
5) Topped off all the fluids
6) Changed the air filter

The only two things that I am not sure about is the ignition coils, spark plug wires and the O2 sensors.

Please suggest what I need to do next I was planning on keeping this car forever until it dies completely. The biggest thing I hate is wasting gas.

Thank you fellas.

dj_gallito83

you could change the fuel filter, pvc valve, fuel system cleaner (not the one that you just pour into the gas tank)

htekken

i was gonna mention fuel filter as well.

djcrunkmix

I will go ahead and replace the fuel filter this weekend. I also googled and found that PCV valve also needs a replacement. (Does anyone know where the fuel filter and PCV valve is located on the 2001 Accord V6?)

I have always wondered this: What if, hypothetically speaking, one of the spark plug is bad and doesn't spark or the wire has too much resistance to create a sufficient arc? Would the engine light go off and tell me that one of the cylinders isn't firing? If not, I would just be wasting un-ignited fuel through the exhaust, causing inefficiency.

nhldogg

Isnt the fuel filter inside the gas tank on these cars? If so how would you replace it?

tamadrummer1120

the ecu would detect that as a misfire as it would not be firing.

dj_gallito83

the fuel pump is in the gas tank. the fuel filter should be near the firewall.

djcrunkmix

Do you guys think that I should also check up on the O2 sensor? I never got an engine light for a faulty O2 sensor. Is it possible that it might misreading but the ecu doesn't know it?

Any other possible suggestions besides fuel filter?

htekken

well besides fuel filter, o2 sensor and spark plug wires. those were already suggested, i would replace those anyway, regardless of a CEL.

KWayRacing

OK
The fuel filter isn't serviceable as it is part of the in tank fuel pump assembly. Its more like a screen or sock pick up.

Your car doesn't have spark plug wires. It is equipped with COP (coil on plug) Coils at each of the cylinders. COP failures are 99% of the time connected with check engine light and DTCs stored for that corresponding cylinder misfire and maybe a few more, but when a coil fails it is very noticeable to the ECU and also to you.

To accuratley diagnose 02 sensor or fuel trim problems you really need scan tool data unless you don't mind wasting money trying things and waiting a week to find the results.

THere is such a phenomena known as a lazy o2 sensor. Its a sensor that the heater circuit is good in but that has a difficult time sending a steadily changeing signal to the ecu. SO it is possible to have a faulty o2 sensor without a CEL but it is not the norm. Again scan tool data is key.

Aside Your list of maintenance did not list Timing Belt replacement. While I am not suggesting that a timing belt service will increase gas mileage it still would be past due and definitely more important to attend to than getting better fuel economy. With a broken T belt your car would get 0 MPG have 0HP.)

Any competent import repair facility should have no problem diagnosing fuel trim problems.

djcrunkmix

@KWayRacing

Thank you very much for your advice. I guess the coils are fine then. Timing belt was replaced by a technician at 110K miles. I have since driven the car for another 20K (total 130K).

Should I take the O2 sensor out and take it to a mechanic for a scan test?

Also, you said I won't be able to service/replace the fuel filter? Do you think I should clean the throttle body/PCV?

KWayRacing

The O2 will have to be tested dynamically. Meaning it will have to be tested while it is in the car and being used. Using a scan tool capable of viewing live data pertaing to fuel trim and particularly o2 voltage switching. Other values are important to view at the same time. MAP sensor voltage EGR VLS and a few others.Replacing the PCV valve is probalbly eaiser and more effective than cleaning it. I think its service interval is every 60k which would be past due for replacement for the second time. Cleaning the throttle body would be completely ineffective in chasing fuel mileage concerns. I am intersted in the at idle map sensor voltage reading.

phootbag

I agree with the above. Being that your car is nearly completely computer controlled, the only real way to make sure it's running correctly is to inspect applicable lines of data as mention, EGR VLS, ST fuel trim, MAP voltage at warm idle, ECT, FSS to make sure it's entering closed loop, and if you REALLY want to know what's going in/coming out, you need to have a 5 gas printout of the tailpipe emissions and enter the data into a Lambda calculator to check the actual air/fuel ratio.

Also, 2mpg isn't a whole lot. Is it possible your calculations are wrong and you aren't burning more fuel than normal? Keep in mind, a slight increase in throttle angle will increase fuel injector duration tremendously and decrease mileage noticably. How you drive, accelerate, going up hills etc will burn more fuel.

Dunne08

Where Do I Go To See Threads About 1:24 Scale Moddeling?

djcrunkmix

I drive extremely conservatively. Infact, I don't let the revs go above 2500 rpm. Also, I am pretty damn sure that I've calculated the mileage correctly.

Oh well, I am going to see what I can do this weekend. I'll post an update soon. Thanks everybody.

millerman61

The problem may just be the 10% ethanol gas we are all forced to use now. Not as much energy in the gas anymore.

KWayRacing

I would like to tell the gas station that 10% of my money is monopoly money and see if that flies the other way. Well it is "comparable" to real money.

JaiYu

the mileage on my 99 accord ex v6 is bad as well... average around 18mpg... will give full tune up and report back.

graham_h

my milage is poor too
my v6 honda uses more fuel than my 4.0ltr ford !!
Going to replace the fuel pump and sender unit and see what happens

cnr

My 2001 V6 accord WAS suffering the symptoms mentioned above by other members. I took it to a trusted mechanic. He found a exhaust leak just above the o2 sensor, near the engine. The o2 sensor was fine, all diagnostic signals from the computer in test mode came back fine too. I have better millage than a new 2001 accord now.

75aces

Remove extra items from youir trunk and double check tire pressure at next fillup. Doesn't hurt to use fuel injection cleaner. Worked on my 96 accord ex 4 cylinder. I used to average 330 miles on a tank. I currently average 350. This is mostly around town. When I blend in freeway mileage, I get up to 360.

king_pin

Don't forget the importance of valve adjustment!