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Discussion Starter #1
My 2007 Honda pilot is getting 8 MPG
with no sign of a problem to fix.
I normally get 18-20 MPG
The engine dummy light hasn't come on.
No gas smell or leak I can see.
Engine runs perfectly with no hesitation or rough running.
Air filter is new.
Anyone have some insight?
Please help.
 

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How do you know the mileage and how long ago did it start in terms of time, miles and gas tanks?
Mileage? Did you check the plugs or looked at fuel trims?
 

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Discussion Starter #3
I filled up and reset the OD, drove it 115 miles and filled back up.
It started less then 750 miles ago.
tires are at 40 psi
Plugs are good.
How do I look at the fuel trims?
 

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Check the air intake duct for cracks around the TB side clamp before you do anything else. If you have a huge vacuum leak there, the ECU may be trying to compensate.

You would need a software which can read OBDII data and show real-time data including fuel trims. If you get very low trims which go into negatives, then your injectors might be leaking or pressure regulator stuck on closed. If you read large positive fuel trims, then you have a bad O2 sensor or a vacuum leak. In both cases the car may drive fine.
 
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I recently had a similar issue with my 2005 Pilot EX with over 200,000 miles. The gas mileage suddenly went down to 11 and I use to get about 17 around town. Still ran perfectly. I replaced both of the O2 sensors before the catalytic converters and everything went back to normal. They are expensive, though. Each sensor was $165.
 

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$40 at Rock Auto before member's discount. Your choice: Denso or NTK.
 

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18 to 20 is about normal on the freeway with these old Pilots. I'd expect 14 to 16 if I'm doing regular stop and go in the city. Remember these are a 4,400 pound 4 geared, 3.5 liter engined SUV so they will never get what a modern little 2,600 pound, 2.5 liter, 6 to 9 geared SUV gets.

Check your tire pressure. Low pressure adds drag to the rolling tires and wears out the tire edges way early. Worn out tires and crappy tire quality also trashes mileage.

Always start with a complete tuneup. Air filters, plugs, EGR valve, good fluids. Be very aware of the transmission, transfer case and rear differential. Once those are eliminated, clean the MAS (Mass Airflow Sensor), If it is dirty, it will read the wrong amount of air traveling through the air filter to the engine and screw up the air to fuel mixture. Don't use a intake cleaner of any type until you have had a chance to look at the old plugs. They should all have the same wear and look about the same. If they don't, you have a more serious issue affecting the firing balance between the cylinders.

After removing the engine port cover and scraping all the burnt crap out of the EGR ports, run a full can of B&G K44 intake cleaner though the tank with a load of premium. K44 is light years better than the other stuff out there. Be sure to replace the cover gasket when you do this. After this run two cans of CataClean following the instructions carefully, to clean out the Calalitic Converter and Exhaust system. Crap in the Cats will increase the back pressure in the exhaust system, changing the temperature being read by the O2 sensors and muckup the air flow mixture

O2 sensors can help. Most of the time when they fail you will get a sudden drop in mileage. They are expensive and the cheap aftermarket replacements can often be worse that the old used originals. Often they can be unplugged, pulled and cleaned without having to replace them. You may find the CataClean has done the cleaning job for you. Sometimes just unplugging them and plugging them back in will work off corrosion in the plug making them good again. If you can get access to a code reader that monitors an engine while it is running, most readers can do this, you will see able to see what voltages the O2 sensors are sending to the computer. It will vary between 0 and 1 volts. Any pauses or over 1 volt readings will indicate a bad sensor. This test must be done with the engine at full operating temperature. This is an easy, cheap test. You could do this first, but definitely do this before chasing after new O2 sensors.

Hope this helps
Gill
 

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Check the coolant temp sensor. Have the function checked out with a scan tool. If the sensor has failed, the computer will be stuck in warm-up mode (open loop). Open loop is a default, pre-programmed rich mixture mode. Once the engine is warmed up, the ECU goes to closed loop, and fuel is controlled by real time feedback information.

Consider replacing the fuel pressure regulator. The diaphragm can fail, and allow excess fuel to leak into the intake manifold. This is also associated with hot start problems, due to flooding from fuel leakage.

And consider replacing the fuel injectors, although that would not be at the top of my list.
 
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