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Discussion Starter · #1 ·
Hi, old visitor of the forum but this is my first post...Sorry to introduce myself in this way.
I bought an Accord 2007 V6 EX-L 2 Months Ago and i have done almost everything recommended here when you buy an used Accord. Until today this is what I've done:

Oil Change
Oil Filter Change
Air Filter Change
Spark Plugs
Transmission 3X Drain & Flush with genuine Honda DW-1
Transmission Filter
Coolant Flush & Refill with genuine Honda Coolant
Power Steering Flush.
Brake Fluid Change
Throttle Body Cleaning
PCV Valve Inspection & Cleaning
MAP Sensor Cleaning

No check engine light and no codes at all.
Even I've done all this i'm still getting a crappy mileage of 13 MPG in city and 16 MPG at highway.

I have a WiFi OBD2 adapter and iPad setup to diagnose and monitor my car and since 2 days I've been monitoring the Fuel Trims ( Long & Short ) and noticed that they are really high even after an ECU Reset and all the maintenance I did.
Long Term Fuel Trim 6.5
Short Term Fuel Trim 11.2
This is at Idle...when the car is running as you know...they keep changing up & down. But the Long Term Fuel Trim in rare conditions returns to a lower number...it keeps going up.
Please help!:paranoid::paranoid::paranoid:

Here's a picture when the Long Term Trim with a lower value but you can see how high is the Short Term Trim.
 

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Seems that you have an air leak and the ECU is trying to compensate by adding fuel. You will have to check all hoses and connections from the intake manifold. Not an easy task.

Good luck!
 

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Welcome! That is quite the first post- written like a pro and 100% pro-active on maintenance! Not an expert here on fuel systems, but, every now and then someone will post here with very low mpg numbers- and if the car is otherwise well-maintained it is often a cracked throttle body as Accord_CL mentioned.

I assume since you are on top of maintenance the tires and tire pressure are within spec.

Which city are you in?
Which formula/method are you using to calculate your mpg?
 

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Discussion Starter · #5 ·
Welcome! That is quite the first post- written like a pro and 100% pro-active on maintenance! Not an expert here on fuel systems, but, every now and then someone will post here with very low mpg numbers- and if the car is otherwise well-maintained it is often a cracked throttle body as Accord_CL mentioned.

I assume since you are on top of maintenance the tires and tire pressure are within spec.

Which city are you in?
Which formula/method are you using to calculate your mpg?
Thanks Rick, if I do something correct about maintenance I have to say thanks to this great forum and members like you who provide valuable technical information to everyone who need it.

I'm in Santo Domingo, Dominican Republic and I use the fill up/odometer method plus the DashCommand App which provide very similar resuts.
One more detail that I like to add is that the fuel here is known to be inferior to the fuel from USA, I expect to not get the same MPG as in USA but I even monitored a friend's Accord 2004 V6 and the Fuel Trims Values were more acceptable than mine and he is using his car in the same city and with same fuel brand/station that I use.
Thanks

After you cleaned your throttle body, did you do the idle relearn procedure?
Thanks for your answer Ryan, yes after the ECU Reset I did the Relearn Procedure.
 

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@Accord2007V6: Thank you for the compliment :) We all try to help. And thank you for answering the questions directly.

1) How many miles/km are on your car?
2) What did your old spark plugs look like? Where they "dry" and "brownish", or a little wet, black, and fouled?
3) Just checking on the fuel again- in the DR you guys run 10% ethanol, 15% ethanol, or are you 100% pure gas? I ask because I know Brazil provides some of the fuel there.
4) If it is a vacuum leak (cracked throttle body), then one video that has helped me in the past is this:
http://www.youtube.com/watch?v=9CPqbaSgcok

You can use the propane method or the carb cleaner method.

The spark plugs do not lie....but since yours are new I don't know if reading them at this point would be helpful....

Waiting for more experienced minds to chime in.....
 

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Discussion Starter · #8 ·
@Accord2007V6: Thank you for the compliment :) We all try to help. And thank you for answering the questions directly.

1) How many miles/km are on your car?
2) What did your old spark plugs look like? Where they "dry" and "brownish", or a little wet, black, and fouled?
3) Just checking on the fuel again- in the DR you guys run 10% ethanol, 15% ethanol, or are you 100% pure gas? I ask because I know Brazil provides some of the fuel there.
4) If it is a vacuum leak (cracked throttle body), then one video that has helped me in the past is this:
http://www.youtube.com/watch?v=9CPqbaSgcok

You can use the propane method or the carb cleaner method.

The spark plugs do not lie....but since yours are new I don't know if reading them at this point would be helpful....

Waiting for more experienced minds to chime in.....
1-85,000
2-I'm not 100% sure but if I think they were Dry & Brownish.
3-I really have no idea as they don't provide that info clearly.
4-Will do that test and let you guys know the results.

Thanks Again :thmsup:

O2 sensors??
That would be my third item to check, if it is not a vacuum leak which is first in my list of suspects my second would be injectors in need of a good cleaning, stiil waiting for my order of SeaFoam to do that as it is not available here.
The third would be O2 Sensors

What do you guys think?
 

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There was another post about a guy wondering about his gas mileage. Although his O2 sensors weren't really bad, he changed them out and gained 1mpg. He discovered this by voltage readings on the O2 sensors.
 

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vacuum leak?

I may have missed the response but, have you put time into looking for a vacuum leak like Accord CL mentioned? I had a similar problem and it was a hairline crack in the air tube (accordion tube) connecting to the air box to the throttle body. It will Not necessarily throw a TDC. It's worth a look.
 

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Discussion Starter · #12 ·
I may have missed the response but, have you put time into looking for a vacuum leak like Accord CL mentioned? I had a similar problem and it was a hairline crack in the air tube (accordion tube) connecting to the air box to the throttle body. It will Not necessarily throw a TDC. It's worth a look.
Thanks for your answer, I did the leak check with a propane torch and no leaks found, I'm waiting for my order of SeaFoam as a last resort to see if it is an injector efficiency problem. Will post results.

Can anyone confirm if I can run the SeaFoam without fouling my Spark Plugs which are practicaly new?

Thanks in advance.
 

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The fuel trim numbers are normally given on a bank by bank basis, so in a V engine you have 2 banks, just wondering if both banks are the same or if one bank is better than the other. Also remember that long term fuel term numbers are stored in the ECU and short term numbers are not stored.

Some other sources of extra air in the intake are

1. Power brake booster
2. PCV valve
3. EGR valve
4. EVAP system
5. Oil dipstick, oil cap

The other issue could be the MAP sensor not working correctly

Another possibility is the O2 sensor(s) before the Cat slow switching.

Also be sure all temp sensors are reading correctly
 

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Discussion Starter · #14 ·
Update:

I did the SeaFoam cleaning...not too much smoke,I guess this is good :dunno:

I feel a small improvement in Throttle response but my fuel economy is still really low, my fuel trims still are the same as before the SeaFoam.

Removed EGR Valve and cleaned. No change

Several ECU Resets and Idle relearn after each process.

Vacuum Leak Check with Propane Torch....None found.

I don't know what else to try. :dunno::dunno::dunno:


Please

Can you guys share some values for this V6 engine so I can compare with mine. Values like MAP readings at Idle, Ignition Advance at idle, Fuel Trims at Idle?

Thanks in advance.
 

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I do not own a V6, but as long as you have check for vacuum leaks and found none, your issue may be slow switching primary O2 sensors. There is another thread where they replaced the primary O2 sensors and the fuel trims moved close to 0 and the mileage increased. It sounds like you have done the normal things, cleaned the throttle body, EGR, and MAF sensor. You can adjust the valves clean the fuel injectors, set your tire pressure, make sure there is no I restriction on the exhaust (replacing the exhaust with a larger diameter pipe will help), cold air intake. Make sure all brakes are not dragging and all wheel bearings are good.


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