Decreased Gas Milegae and Random Check Engine Light
 

Hi All:

So here's my mystery with as much information as I think is relevant at this point.

2005 accord lx 4dr 4 cyl
150,000 miles
Drive 45 miles to work (45 home) and normally get 28-30mpg

At 110k I got a flat on my mile ride home from work and didn't notice it for a while - was able to get the tire patched, but the car never rode the same since.

So at 115k I got new tires. got an alignment (although the shop didn't have the computer print out for me that I requested). Car pulled left. Shop balanced and rotated tires - better but still pulling. Shop said rim might be slightly bent - they had no other ideas.

Over the next 10k that pull to the left got better by itself!? Have rotated tires regularly since - feel slight pull after initial rotation, but nothing too bad...

140k Trip to SC this summer - gas pedal starts vibrating badly. feel like cv joint. had to replace both front axles.

Fast forward to 150k

Have Honda drain and fill tranny, drain and fill radiator, and change oil.
I changed my spark plugs myself and put in new NGKs (first spark plug change ever -- yes i know over recommended mileage)
Got a tire rotation.

first tank of gas afterwards...Gas Mileage drops to 24/25mpg.
2nd tank of gas -- mileage seems better through the first few miles - then check engine light goes on. Drive on it for 2 days. Then don't drive the car for 4 days. start it up to go get code read - Light is OFF

the next 2 weeks, gas mileage back down 24/25.
week before christmas - fresh tank of gas, light turns on. check that gas cap is on tight (and prepare to drive it a while to reset). Next day CEL off.

Since then, no Check engine light. Car pulls left - and mileage still at 24/25 mpg (regardless of gas station)

I am not sure where to go at this point.....

Alignment and just drive until CEL maybe goes on again and quickly get it read?
Get rims checked (how?) to see if they're bent?

Did I do something wrong with the spark plugs? (left them at gap that I received them at)

Gas Cap?

ANY suggestions would be greatly appreciated.

Thanks for reading all that.

The code still should be stored even when the check engine light is turned off. Stop by a parts store and have the codes read.

For the pulling, I would check for loose suspension components. There is a good ericthecarguy video on finding suspension noises that may help. A shop should be able to determine why your car is pulling on you.

Went down to autozone for codes.

Light had been off since december 22 mind you.

Code came up as PO139 secondary o2 sensor.

Now - I had this sensor replaced 2 years ago when I had a constant check engine light on.

Somehow related back to spark plugs causing a ratio issue?

busted cat?

Sensor died again?

Any thoughts?

Update:

My CEL went off in early january and hadn't come on until just last week. It was on for 2 days - then off. Then came on again last night. I went back to autozone and now it's throwing both

po139
and
po341

As soon as autozone finished checking code, started car and light off again.

This weekend I plan to pull the plugs out and reinstall. Autozone guy thought maybe the honeycomb in the cat broke off and was maybe blocking emissions?

No idea.....

Any new thoughts? troubleshooting methods beside buying a new sensor.

Try applying a bottle of Cataclean ($25), then a bottle of seafoam ($8). They're supposed to help clean the sensor as well as the cat. On top of that, they improve the mileage by several mpgs. I can attest to that!

P0139=slow response from 2nd O2=do you have a way to graph it or other tests.

P0341- I've got two listed in my cheat sheet....looks like I need to find the right answer. One is towards the vtec and the other is the cam sensor.

To me, the cat is fine.

I would be concerned about the P0341. That is for a cam and crank sensor out of phase.

It could be the cam sensor.

The other possibility is that the timing chain is stretched past the point where the tensioner can keep it tight. Just search the web for P0341 for honda accord and acura tsx posts.

This is something that you do not want to ignore, because you do not want the timing chain to jump teeth and mess up the engine. There should be an access cover to see how far the timing chain tensioner is pushed out.

From the 2003-2006 Helm shop manual:
P0341 = Cam-position sensor (CMP) & crankshaft-position sensor (CKP) are out of phase.

To me that sounds like cam timing is off???

I sold that Helm book after selling that car, so I can't look up the actual troubleshooting chart that goes along with the code.

UPDATE:

I check plugs again - gapped properly, in correctly, colored white, etc. Pulled negative off battery to reset all.

No more po139! BUT.....now I have an intermittent P0341

When I start the car in the morning - it comes on. stays on for my hour commute to work. stays on my entire commute home from work. Then when I go to the gym at night - its off and stays off - multiple start and stop - until the next morning when i start it up.

Ive read some posts on here indicating chain issues, but being intermittent, could it just be the sensor...?

Got oil changed yesterday @ Honda and they said the chain did seem a little loose - of course they offered to replace for $1000...Any ways to check? Anyone thinking it might be a loose sensor...?

Afterall, All these issues started after I changed my spark plugs...never had an issue before.

Does anyone have a diagram of where its located so I can check if its in snug, etc. googled for a while and not finding anything helpful...

Thanks!
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