Lean or rich condition? Confused

[Bobi T]

Hi,
I have a 2008 civic hatchback (uk made). I neglected this car from 100k km to 140k km then decided to take care of it. Most maintenance went smooth then I saw the service schedule and found out spark plugs change at 120k km has to be done. So pulled out the spark plugs and they had a strong white deposit on the earth tip (side tip). As other than that the spark plugs were as good as new and super clean. I understand this indicates engine running in lean condition.

On the other hand my oil smells a lot like gasoline. As I understand this might indicate rich condition.

So I am super confused. Am I missing anything? Anybody to guide me to the right direction?

Topic

[Dave Tidman]

I would look at your fuel trims with live data, that will tell you which way it is running. Do you have an codes from the ecm?

Here is a good short video on fuel trims:

[Bobi T]

Thanks for the video!

So according to what I learned from the video:

* My O2 sensor looks fine reporting between 0.7 to 0.1 and always fluctuating
* My short term trim levels though jump up and down quite a bit though. While driving in the city usually jumps to positive +20 or so then spend a lot of time in the
negative -5 and negative -10 area. It usually is in the low side around -3 while cruising or idling.
* Long term trim levels usually either -4 or close to zero never seeing a plus.
* My air fuel ratio looks quite healthy always around 14.7 except gear shifts.

As I understand this means that it might be running a slight rich condition which does not explain the clean and shiny spark plugs with white deposits.
In the end according to the video I have to check a lot of things like exhaust, vacuum leaks, sensor health etc.
So I guess there is no direct answer here. However you might answer two easier questions.

q1. The valve clearences has never been adjusted in this car. Can it be the cause?
q2. Although I thought spark plugs were ok I am not a mechanic so maybe they are not so ok. Can this be the cause?

• This reply was modified 4 years, 4 months ago by Bobi T.

[Dave Tidman]

If your LT fuel trim is between -10 and +10, I wouldn’t worry about it. You will never achieve a LT fuel trim of 0. Your ECM will throw a code when it’s time to start worrying.

for Q1, valve clearance is not much of a factor, but it is important in Hobdas to keep then adjusted to avoid other issues. On the second question, the plugs are probably OK.

[Jeffrey Voight]

Your fuel trims are good and O2 sensors are good. I would check your service schedule and make sure everything is up to date. For your I might do a wet\dry compression test to check for worn rings, and replace PCV to address the smell of gas in your oil.

[Bobi T]

Dave and Jeffrey, thanks for all the information it has been really helpful.

I catched up with the service schedule except the spark plugs and fuel filter in the tank(no seperate filter).

I’ll try to compression test I understand the concept. However when you say PCV is it just the PCV valve I have to check/replace or are there more types of common failures with PCV system?

[Bobi T]

So removed the pcv valve and checked. It’s super clean and looks like it’s working. This is confirmed by reinstalling it and squeezing the hose which made the engine stall. So it is sucking air from crank case.

However I realized when I open my oil cap while engine is running there is quite a lot of pressure and it blows out gasoline vapor.pretty much constant. This made me belive that my rings are worn and the pcv system is just not enough to equalize the pressure so it’s pretty much stays open all the time. Does it make sense?

But the real question is should I do anything about this? My engine oil level does not increase se(last oil change February) so its only vapor leaking.

[Bobi T]

Well I did the compression test and it was 230 psi across all cylinders. So my theory goes down in the trash. Piston rings and valves are OK. No idea why the oil smells like gasoline.

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