So I just had a new serpentine belt and my 180k service done. Now I am running too lean and getting misfires across the board. I know my upper O2 sensor was going out, but it is ... Odd that immediately after honda services my hybrid I suddenly go lean and my fuel milage drops to 18mpg and no acel. Any suggestions before I go back to honda when they reopen?

 

An upper O2 sensor going out can wreak havoc on the mixture. A lean condition can cause misfires.

I had essentially the same thing happen seemingly at random on my 2006 w/215K miles. Everything was fine, started getting active misfires (flashing CEL) and P030X codes as well as the upper O2 sensor code. Replaced sensor and all 8 plugs. Purred like a kitten.

 

Keith, thanks for the reply. Should I be looking at replacing the coil packs as well (close to 200k) i know the rear bank of spark plugs is a bear to get to you have to have 2 flex adaptors and remove the plastic cowl under the windshield. How hard is it to get to the upper O2 sensor?

 

I only replaced 1 coil pack after replacing the plugs. Once all the codes were gone, I noticed a slight hesitation under accel. It turned out to be one of the front coil packs.

I replaced it with a Hitachi OE Style from RockAuto for about $45.

While I never pay OEM price, I always attempt to buy the OEM equivalent aftermarket part, e.g., ONLY the NGK/Denso plugs for that car. In a parts store, they're about $14 each. You can get them cheaper from RockAuto. Hitachi also made the coil packs for Honda.

With the cowl off, replacing plugs is a cake walk. I can do it without removing the cowl, but the driver's side rear plug coil is hard to remove.

Zero flex adapters are needed, and I don't recommend using them. I used a combination of a long and short extension. IIRC, ratchet, short (about 3"), long (about 6"), plug socket. I would separate it between the long and short extensions as needed.

Do NOT use anti-seize.

O2 sensor is visible behind and below the rear bank of plugs. IIRC, it's a reach, but I had no issues replacing it. You will need an O2 sensor socket.

 

I know i asked this a couple of days ago but do not see the post:

I presume the engie is trying to run rich as the o2 sensor has failed and thinks things are lean. Therefor it does no good to replace the plugs while waiting on the replacement sensor if I am going to have to do any driving I assume as it will simply lead to fouling.

Is that rational or should I go ahead and replace the plugs while I wait? My hybrid is my sole source of transport (gotta love grad school)

 

The more you drive it in this condition, the more likely you are to foul the cat. That will be another $600 or so.

Have you received a code for the O2 sensor, or do you just have P0171?

 

I had previously had the upstream O2 sensor code. The honda dealership cleared all my codes, it has not reappeared but I have only driven it a couple hundred (lit 2) since I got it back and the new codes populated.
First thing I checked was all the hose fittings from intake to manifold to make certain I had no leaks. Found 1 loose fitting, tightened it, cleared my codes again with my obd then let it idle and did some data logging. System it running ,+8 on fuel and that tells me between the lean condition, misfires and such it is likely the previously failing O2, also I am getting misfires across the board, even when idling, so I do not think it is the fuel pump as I would think it would be worse as fuel needs increased not even across the rpm spectrum.

 

On second thought, if the O2 sensor error hasn't returned, I would be hesitant to say conclusively it's the O2 sensor. I would replace the O2 sensor based on the previous code and the age of the car.

P0171 is too lean, and I had it in my head that it was too rich contrary to all evidence provided including my own comments - influenced by the tendency for a failed O2 sensor to cause rich running ...

Anyway, here is the diagnostic process for P0171:

Check for 38-46 psi of fuel pressure. If too high, replace pressure regulator. If too low, check fuel pump and fuel filter. If both are good replace regulator.

If fuel pressure is good check:
PCV valve
PCV hose
EVAP canister purge valve
Throttle body
Intake manifold
Intake air duct

Replace any parts with leaks.

If no leaks, check valve clearances.

It would seem the most likely place to have an issue with low fuel flow is the fuel filter.

 

I understand what you are saying, but given as my data logging is showing that the delivery of fuel is in excess of what it should be, and the O2 sensor was wonky before. I am still thinking that it is the most likely culprit. If it is reading wrong, thinking that the system is lean, and thus increasing the fuel to the cyls that would cause a misfire. It is a common belief that Gasoline is explosive, it is not, it is actually fairly difficult to get Gasoline to explode you have to get a fairly narrow range of O2 and C8H18 to get it to go boom Below the flash point, nadda and above the flash point zone... also nadda.

I wish I had a calibrated sniffer I could check my exhaust and see how much non combusted fuel I have. And that is one of my concerns. When you run rich your cat tries to oxidize all that extra fuel and becomes a very inefficient night light. The O2 sensor comes in on Friday, I wil swap the plugs out, clear the codes swap the O2 sensor and do some idle data logging. I bet my +8 fuel usage drops down to something reasonable. If not, I will take it to Honda and let them test the pressure. What really annoys me is that they supposedly test drove my car before returning it to me and a blinking error light on he dash is something he tech should have noticed.

Now it could def be the filter, They put some kind of fuel methanol treatment in it as part of the 180k service if something broke loose in the high pressure side, returned via the bypass to the low pressure side and fouled the in tank filter then it is possible I have a new filter issue, but f I recall correctly the primary filter for the HCHII is in the tank with the pump isn't it? r is it on the firewall like a normal Honda?

 

You are correct. It's in the tank. I've owned too many vehicles. I thought it had an in-line filter.