Cause for drop in gas mileage

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Old 06-19-20, 12:56 PM
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Cause for drop in gas mileage

I have a 2016 Honda Odyssey with 65K miles. At about 62.5K miles the mileage suddenly dropped by about 10%. It dropped the most for in town driving, but also some for highway. It also occasionally has a very slight miss. Otherwise, I can't tell it runs any differently. Can you suggest what might have caused this to happen so suddenly?
 
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Old 06-19-20, 12:59 PM
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Could be a fouled plug but they usually go further than that these days. Check all the plug wires for damage and make sure they are securely attached to the spark plug. Do you buy gas from the same place? A sticking caliper can cause drag which would lower the mpg.
 
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Old 06-19-20, 02:45 PM
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I'd take it in and have them run a scan on it. that should narrow it down to what's wrong if it's the engine.
Has the check engine light been coming on?
 
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Old 06-20-20, 07:17 AM
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No. The check engine light has not come on.
 
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Old 06-20-20, 07:33 AM
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Still wouldn't hurt to get it scanned.
 
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Old 06-20-20, 10:34 AM
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Most likely due for an overall tune up. New plugs and wires, injectors cleaned, timing adjusted, belts replaced, tire pressure up to snuff and the correct tire size. All pollution stuff needs cleaning or replacing. Oxygen sensors, catalytic converter checked. Looking at about $1000 bill.
 
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Old 06-21-20, 12:29 PM
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1. air filter
2. he does not have plug wires.
3. city driving. CITY DRIVING.
It's too early for new plugs at such mileage. Those engines are workhorses.
 
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Old 06-21-20, 01:43 PM
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Are you running the 88 octane or the 87? The 88 will cause you a slight loss in power and mileage if your vehicle isn't a flex fuel vehicle.
 
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Old 06-21-20, 02:52 PM
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I use 87 Octane. My driving is about 1/2 city and 1/2 highway. When I go on a trip, the highway is also down about 10% from the general average over the previous 60K miles.
 
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Old 06-21-20, 03:41 PM
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Air filter.
Otherwise, check tire pressure. Was any extra load added lately? It's same engine as in Honda Ridgeline, very reliable and does not have enough miles for age problems.
 
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Old 06-21-20, 06:32 PM
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Thank you for all your comments and suggestions. I maintain my tires at 35 psi and check them frequently. I know this is more than the 33 that Honda specifies, but I just feel a little better without so much bulge at 33. No heavy loads. I think I will just ask for the scan when I take it in for the next oil change which will be soon - every 6K.
 
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Old 06-21-20, 07:37 PM
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Sounds like spark plug fouling.

Seems similar to a known defect where piston rings to align and douse the cylinder in oil. This was the subject of a warranty extension and class action lawsuit about 2011-2013 models. The fix ain't pretty.

2011–13 Odyssey: Replace piston rings 1–3 and replace spark plugs 1–4 (includes diagnosis). 8.5 hr
2011–13 Odyssey: Add to update the PCM on 2011 Odyssey only. 0.1 hrs
2011–13 Odyssey: Add if replacing piston rings on cylinder 4. 0.8 hrs

-American Honda is announcing a powertrain warranty extension as a result of a settlement of a class action captioned, Soto et al. v. American Honda Motor Co., Inc., Case No. 3:12-cv-1377-SI (N.D. Cal.). The piston rings on certain cylinders may rotate and align which can lead to spark plug fouling. This can set DTCs P0301 through P0304 and cause the MIL to come on. American Honda is extending the powertrain warranty to cover repairs related to engine misfire (that triggers DTCs P0301 through P0304) to 8 years with unlimited mileage from the original date of purchase and has settled a class action based on this remedial measure. This warranty extension does not apply to any vehicle that has ever been declared a total loss or sold for salvage by a financial institution or insurer, or has a branded or similar title under any state’s law
https://techinfo.honda.com/rjanisis/...eb/A13-081.pdf
Disclosure - I'm a Realtor and Attorney, but I'm not YOUR Realtor or Attorney.
 
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Old 06-22-20, 08:14 AM
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If you do not have CEL, there will be no codes.
It might be as simple as bad gas batch. Are you hopping gas stations and going the forsaken places like AM/PM and similar or, sticking to same gas station?
Something is choking your engine, something minor that does not trip CEL.
And, in all time of posts here - did you, actually, check air filter?


PS. Locate main ECM fuse(-s, may be several) and pull them all out for 10-15 minutes, to reset ECM.
 
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Old 06-22-20, 10:19 AM
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There is a possibility that there may be "pending" codes that have not yet caused the CEL to set. The scanner I have will note these codes with a (P) after them. An actual misfire should set a CEL immediately, but I've had other codes (such as O2 sensor) show up as pending -- and then either set a CEL later, or clear themselves.

https://www.nyvip.org/PublicSite/OBD...ble-codes.html

"Pending codes are caused by intermittent faults or faults that the PCM needs to see happen in two consecutive warm-up cycles to set the code. If the fault does not reappear within 40 warm-up cycles, the code will be cleared from memory. If the fault reappears for the specified number of times, the code will then mature into a diagnostic trouble code (DTC) and the PCM will command the check engine light to illuminate."
 
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Old 06-22-20, 11:49 AM
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I did check the air filter and it appears dirty - certainly more so than I would like. I will replace it immediately. Thank you for the suggestion. It also feels slightly oily or greasy. Is that normal?
 
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