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4 Posts
Discussion Starter #1
2008 FWD 150K miles on engine. Getting 18mpgs in the city, 23 on the highway.

What鈥檚 been done:
  • Engine Air Filter
  • Engine Oil
  • Spark Plugs
  • Tire Pressure
  • Clean MAF sensor
  • Techron Fuel System Cleaner
  • BG44k
  • Italian tuneup 馃槑
Haven鈥檛 tried:
  • Valve adjustment
  • Vacuum leak test
Some OBD2 data (can provide more if needed):
I took some OBD2 scanner data. I need some help interpreting it. To my eye it looks like it is consistently dipping into the lean territory causing my short and long term fuel trim to climb.
  • Could this be a bad sensor problem? If so, which of the sensors should I replace?
  • Is Sensor 1 on the OBD data the "upstream" pre-cat sensor? It does not give me a voltage reading, only amperes (not shown but can share if needed, it looks alot like the Sensor 2 data it stays around 0 then dives down repeatedly)
  • Is Sensor 2 on the OBD data the "downstream" sensor? This gives me voltage
O2 sensor doesn鈥檛 really oscillate stable at idle like I have read that it should.

Aside from MPG, it drives great actually.

Thanks for the help!

186 Posts
Can't see your problem you are getting more or less what it says on the can.


Premium Member
2018 EX-L fwd
588 Posts
Does the "dreaded" CEL orange engine outline show up on you instrument panel?

01 sensor is between exhaust manifold and cat converter. Can see this on the backside of the engine. 02 sensor is between cat converter and muffler. From what I've read, the voltage of the first 02 sensor should fluctuate. The voltage of the second 02 sensor should be constant. The difference being that before it enters the cat converter, the exhaust has a great deal of variability regarding the contents of the exhaust. After passing through the cat converter, the exhaust gases should be fairly homogenous.

Had a similar problem with 2010 Accord - similar engine & exhaust setup. Cleared it by running a can of BG44 and a can of CRC, at different times, of course. Used each with a full tank of top tier fuel, then did an extended highway drive for each application. After second application, began using only top tier gas. Gas from local convenience stores and / or supermarket outlets may not be top tier gas. 02 sensors resumed normal functioning. Haven't had the CEL turn on yet. [knock, knock]

And, as always, with regards fuel mileage, the most important factor is your right foot. Back in 60's, driver training instructors always said to drive as if there was a raw egg under your right foot. Another way of looking at that is to compare your tach with the fuel gauge. The more revs shown on your tach, the less amount of gas you'll have in your tank.

Hope this helps. Keep us informed.

2007 CRV
17 Posts
First O2 sensor is used to adjust the fuel/air mixture
And its readings should fluctuate as the mixture is adjusted by changing the pulse width signal sent to the fuel injectors
Second O2 sensor is used to monitor the efficiency of the catalytic converter.
If they need to be replaced then should use OEM parts

As Kazoo2U says, the way you drive determines your gas mileage.
And from what you say you get, you are doing better than me.

1,828 Posts
Gasoline plays a big part in it also--the more ethanol mixed into it, the lower your gas mileage will be. Ethanol is higher octane but stores less energy than gasoline, therefore it requires more ethanol to go the same distance. On road trips, I've noticed as much as a 5-6 MPG difference in various tankfuls of gas.
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