The mileage we are getting on our Honda Odyssey has dropped quite a bit over the past few months.

2006 Odyssey
179,000 miles

Had a check engine light on a few weeks back so took it to both NAPA and AutoZone to have their code readers hooked up to give some possible reasons for the check engine light.

Code reader suggested:

- bad plugs on cylinders 1,4,5
- bad coil packs on cylinders 1,4,5
- oxygen sensor
- camshaft position sensor

Changed the oil and filter because it was time. Changed all six plugs.

Coil packs looked ok but I don't know how to test them to see if they are ok.

I've had a camshaft position sensor go out on another vehicle. It was REALLY noticeable and sounded like a high performance cam under the hood when you started it. This doesn't seem like a camshaft position sensor unless there are different levels of "how bad" they are going out.

Needed to get an inspection so I took it to our mechanic. They cleared the codes, drove it, and it threw a code for a sensor for air/fuel mixture just before the catalytic converter. Sorry, don't recall the exact name of the sensor.

Had the mechanic change the sensor. It hasn't thrown any codes since then.

Mileage has not improved. I'm getting a good 100 miles per tank less than I used to.

What does the auto board recommend?

New fuel filter?
Run some fuel treatment in the tank and take it out for some highway driving?
Replace the oxygen sensor?

Thanks in advance.

Loss of power? Cat plugged?

A coil can look ok visibly but may not be throwing a hint of spark.

If that's the case, it's not igniting fuel in the cylinder causing the car to run rich. That would set off the o2 sensor for sure and make for sh*tty performance/gas mileage.

No LS swap?

I believe it's a given at this point

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The mileage we are getting on our Honda Odyssey has dropped quite a bit over the past few months.

2006 Odyssey
179,000 miles

Had a check engine light on a few weeks back so took it to both NAPA and AutoZone to have their code readers hooked up to give some possible reasons for the check engine light.

Code reader suggested:

- bad plugs on cylinders 1,4,5
- bad coil packs on cylinders 1,4,5
- oxygen sensor
- camshaft position sensor

Changed the oil and filter because it was time. Changed all six plugs.

Coil packs looked ok but I don't know how to test them to see if they are ok.

I've had a camshaft position sensor go out on another vehicle. It was REALLY noticeable and sounded like a high performance cam under the hood when you started it. This doesn't seem like a camshaft position sensor unless there are different levels of "how bad" they are going out.

Needed to get an inspection so I took it to our mechanic. They cleared the codes, drove it, and it threw a code for a sensor for air/fuel mixture just before the catalytic converter. Sorry, don't recall the exact name of the sensor.

Had the mechanic change the sensor. It hasn't thrown any codes since then.

Mileage has not improved. I'm getting a good 100 miles per tank less than I used to.

What does the auto board recommend?

New fuel filter?
Run some fuel treatment in the tank and take it out for some highway driving?
Replace the oxygen sensor?

Thanks in advance.

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In tank non servicable fuel filter.

Summer Gas.

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In tank non servicable fuel filter.

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YIKES! New fuel tank?

how much are coil packs? I would just replace them

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how much are coil packs? I would just replace them

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about $20 a pop on Rockauto.com.

I'm certainly not liking the gas tank fuel filter idea.

Could a few coil packs make such an impact on mileage?

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Loss of power? Cat plugged?

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Power seems to be steady. I haven't noticed a drop off.

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I'm certainly not liking the gas tank fuel filter idea.

Could a few coil packs make such an impact on mileage?

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Yes. But if the packs were bad you would likely get the code again.

When was the last time you changed the air filter?

You dont have coil packs.

This is a coil pack:

Typically a pack of coils that has wires that go to each plug.



Your odyssey has individual COP (Coil on Plug) ignition.
One coil for each plug


Typically if a COP unit is not working correctly, you will have rough idle, check engine light on or even flashing. If a coil is failing but the misfires per 1000 was below the PCM threshold, you'd feel it a little bit at idle or harder acceleration, but not enough to throw an engine light.

Once you changed your plugs, you've verified that the engine is running ok and has NO codes,
its time to look at other things.

1. Is the VCM system working properly?

2. When was the timing belt last replaced?

3. Check things like severely under inflated tires, worn or bent suspension components, out of alignment etc that could cause drag.

4. Have you actually hand calculated the mileage to verify what the current MPG is?

5. How about some Fuel Injector cleaner? BG44K?

There are several posts on the honda forums where people have complained about the first gen ECM engines tend to have this trend of declining fuel mileage as they age, but nobody seems to be able to explain whats happening.

Also regarding fuel filters, many manufacturers are no longer doing them outside of the tank. They just rely on the 'sock' thats inside the tank, part of the pump assembly. I think they were finding too many people not changing the external filters and then causing the pumps to burn up due to the restriction.

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You dont have coil packs.

This is a coil pack:

Typically a pack of coils that has wires that go to each plug.



Your odyssey has individual COP (Coil on Plug) ignition.
One coil for each plug


Typically if a COP unit is not working correctly, you will have rough idle, check engine light on or even flashing. If a coil is failing but the misfires per 1000 was below the PCM threshold, you'd feel it a little bit at idle or harder acceleration, but not enough to throw an engine light.

Once you changed your plugs, you've verified that the engine is running ok and has NO codes,
its time to look at other things.

1. Is the VCM system working properly?

2. When was the timing belt last replaced?

3. Check things like severely under inflated tires, worn or bent suspension components, out of alignment etc that could cause drag.

4. Have you actually hand calculated the mileage to verify what the current MPG is?

5. How about some Fuel Injector cleaner? BG44K?

There are several posts on the honda forums where people have complained about the first gen ECM engines tend to have this trend of declining fuel mileage as they age, but nobody seems to be able to explain whats happening.

Also regarding fuel filters, many manufacturers are no longer doing them outside of the tank. They just rely on the 'sock' thats inside the tank, part of the pump assembly. I think they were finding too many people not changing the external filters and then causing the pumps to burn up due to the restriction.

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Thanks for the reply, and for explaining the difference on coil packs and coil on plug ignition. Interesting that the guys at both parts stores referenced coil packs, as did the mechanic that replaced some on my Tundra a few years back.

1. Don't know about the VCM system working properly. I'll have to do some research and get back to you

2. I know the timing belt has been replaced, probably around 140,000 but I would need to pull records to check and that will have to wait until tomorrow

3. Tire inflation is fine. I check our vehicles monthly to make sure. Wear seems even and alignment doesn't seem to be a problem.

4. Hand calculated after filling up today, I got 15.4mpg on the last tank. Mostly city driving. Was normally in the 22mpg-26mpg range

5. Have not tried injector cleaner but that would be a good thing to do anyway and the easiest next step. I don't expect it to get me 10mpg back, but it can't hurt to run it through

Thanks for the reference to the Honda forums. I'll check that out when I get some free time. Too many things going on at work and home.

It does idle a little tougher than normal at startup, now that I read your explanation under the COP photo.

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When was the last time you changed the air filter?

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Pretty recently. Last oil change or the one before. I looked at it when we changed the plugs. It was pretty clean.

Check those things and report back to us.

What is the mix of driving between city/highway?

Maybe the car needs a good Italian tuneup?

Not much highway driving lately. Not more than 20 minutes on a given day, if that.

I need to take a drive this weekend. I'll take the van and see if it will help.

Hard to find BG products in this town. The place I got some last time is no longer in business, and the other closest place is not open on Saturdays.

I'm doing some highway driving this weekend and had waited to get the fuel treatment. Have not had time during the week and didn't think about possibly needing to order BG products online.

Where can I pick some up in Houston this weekend? Preferably near Kirby and 59 or even near Woodway and Voss.

The BG site showed locations of places that provide BG "services", but is that the same as just selling the products? I don't want a service this weekend, just a bottle of BG44K for future use.

I did go to NAPA and pick up some SeaFoam for use this weekend. Might as well add something for the highway trip.

i always have to buy it on ebay

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i always have to buy it on ebay

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I buy it off of Amazon Marketplace.

Have you checked to make sure the V-Tec has, truly, kicked in, yo?

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Have you checked to make sure the V-Tec has, truly, kicked in, yo?

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It will kick in by the end of the driveway depending on the chromosomal arrangement of the driver. It also brakes in much shorter distances based on said arrangement.

I always buy it off ebay in packs of 6.

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I always buy it off ebay in packs of 6.

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How often do you run it through your vehicle?

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I always buy it off ebay in packs of 6.

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How often do you run it through your vehicle?

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I'd say ever 6-9 months (based on 12-15K a year) is sufficient.

If local (ie bcs)I have some BG injection cleaner.

Filled up Friday. Went to Houston on Saturday and came back on Sunday. Filled up again today.

A little more than half the miles driven on this tank were highway miles, discounting the portions of 290 that were a crawl.

Hand calculated 18.8mpg for the tank.

Maybe this is just what it's going to be for an Odyssey with this many miles, based on the reading I did about VCM's that 1ags mentioned earlier?