Civic 8th Gen, Extremely Bad Short Term Fuel Trim! Need Help!

[syednayl]

Hey Guys, I have been trying to diagnose an issue with my Civic 8th gens Autos sudden horrendous petrol mileage recently. In city it is giving me 6 while on highways 8, which is horrendous given that I got 10 in the city and on the highway id easily get 16,17.

Now I need to diagnose this issue and I have had a look at tons of things like injectors, fuel pump (which I replaced with a Chinese cell which seems to have fixed at least the roughness of the engine) and some other things which didn't contribute towards fixing the mileage situation. I have very bad short term fuel trims on my civic, such as at operating temperatures I am getting consistent -20% -> -15% values regardless of what rpms I am touching be it at idle or not. What should I do to fix this issue, I am currently unsure as to what is causing this issue. I did get a code for rich mixture detection a few months ago which after clearing went away but I am pretty sure that was a sign of things to come. I also believe that the ECU is trying to take away fuel from the mixture which is affecting performance as I have noticed the car has suddenly started to have issues in pick up. Any help would be appreciated. Unable to find long term trim values, on my scanning device for some odd reason but regardless the short term values are insanely bad.

[Hassan1991]

Which scanner you are using?
You need to calculate the total fuel trims.
Have you don't something to injectors recently?
Even though don't anticipate you will start getting 12km/h from this car in city.

[syednayl]

It is a BlueDrive Scanner. Very Good portable scanner.

What is the total fuel trim? There are only short term and long term fuel trims, and FT's for certain banks.

I just cleaned my injectors, nothing else. WIll have them flow tested today.

[Hassan1991]

Which application you are using ?
Switch to other app. Or manually set up Long term fuel trim pid in the settings.
Add STFT and LTFT to get total trims they should be less then 10.
Cleaning injectors sometimes cause then to flow more. That can cause the same situation.

[syednayl]

My Trims are negative ~ -20%for both, just checked. I think this might be a blow issue. The fuel trim get better when I remove the oil cap.

[Xulfiqar]

When you had the rich code, thats when you needed to fix the fault, it maybe a leaking injector or even a bad exhaust oxy sensor lying to the ecu.

If you are constantly getting -15% short trim, im assuming that you are constantly resetting the ecu too because constant short term will set itself into long term and then almost zero itself out.

[pwuser16074435879]

Same mere sath b hai Civic 2010 Prosmatec.
Short trim - 15+ always.
Muje Long trim ki value show nai hoti main b

App kon c App use kar rahe ho?

Mari car main catalytic converter nai hai is ki jaga plate(hole wali) weld ki hoi hai jab main ne purchase ki tab se he.

Or fuel average 7km/L tak de rahi hai.

Agar app ko solution mile to zaror post karna

Thanx.

[syednayl]

I am getting the flow test for the injectors done soon iA, but I took them out recently to clean using carb cleaning spray and none of them showed any signs of leakage (granted that isn't really a way to check perfectly). How would I check the reliability of the O2 on the CAT, is there a readings range? Also, I am getting blow-by, I removed the oil dipstick when at operating temperature (96 C when the fan kicks on) and there was white smoke, this is an intermittent issue. Sometimes it does not happen.

No I am not resetting the ECU, the long term fuel trim is around -17%, and short term fuel trim varies as I accelerate decelerate and sometimes does hit 0 for a couple of seconds but then invariably heads back to -20% -> -10% range. I am not a fan of resetting ECU's because I monitor my cars data quite often.

[Xulfiqar]

what is your long trim when you accelerate?

[Xulfiqar]

How would I check the reliability of the O2 on the CAT, is there a readings range?

Your engine uses an AFR sensor (wide band o2) and Honda has made it pretty simple to diagnose, it shows live current, 0mA is stoich, negative is lean, positive is rich, You should be stable stoich at idle, and should allow a slight rich when accelerating, but settle down on cruise.

If you see wild fluctuations with no change in engine load, its bad.

You can use a supply of LPG to richen the system and test the AFR sensor, Dont use liquid petrol as it may stall the engine.

[syednayl]

Waries in the same range, from -17% to -13%, moves around but never close to 0 ever.

Just did a test at idle. Kept the cap on took my stft readings, came out at -17%. Removed it, immediately went down to -1%, put it back on again, jumped back to -18%, removed it again and it came back down. Not sure what this indicates but thought this might be of use.

[syednayl]

I dont think I follow, but if I have this right, I should plug in my scanner start the car and at idle from the data stream the o2 senser ought to read 0mA, if I accelerate it ought to go to a slight positive (is there a range ? ), and after I let go of the accelerator it ought to go back to 0mA. If at idle it is jumping around or doesnt meet the conditions above then the sensors dead.

I didnt follow the LPG part, are you saying I ought to put some LPG into my gas tank and the o2 sensor at idle should read positive or am I completely not following. because I am pretty sure I am not.

[Xulfiqar]

In a workshop we use an lpg tank with a wand to directly inject lpg to a running engine, it creates a controlled rich condition.

And by what you are writing for testing the afr sensor, im going to assume that you are not a mechanic by trade, to understand it simpler, the fuel adjustment on your engine is very quick, the afr sensor can live control the fuelling and i told you its operating ranges, it should adjust and remain close to 0mA, its the same as toyota except toyota give you a simulated voltage reading instead of amps.

Anyway, if your oil cap is causing trim values to change then you have a pcv problem which is manifesting itself as a trim problem, fix that first and make sure the valve cover and timing cover etc are not leaking anywhere as that can cause a pcv stallout, you should also make sure the breather vent is clean and working, that can cause a pcv stallout too.

[syednayl]

Yeah, I am not a mechanic by trade, but I also don't trust mechanics in Pakistan hence I try to work on my cars to the extent that I can.

So, you don't think this is a blowby issue?

I also thought it was a PCV issue, I took it out and it seemed fine, didnt seem fouled and I replaced it a year ago anyways, I stupidly forgot to do a rattle test and instead I blew on it and it didnt allow any air to cross, whcih I dont think concludes anything.

Should I check the everything such as the intake manifold , valce cover etc incase its allowing unmetered air?

What is a breather vent btw.

[Xulfiqar]

The blowby should be controlled by the pcv unless your engine is a pile of scrap.

The pcv valve can internally break down and cause problems, btw, the breather vent is the tube from the valve cover to the air induction tube.

[pwuser149994783721]

Quite interesting..keep it a bit simple so other can understand as well

[pwuser16074435879]

https://youtu.be/IqxxJG3ryUk part1
https://youtu.be/9OmoqmRo9tI part2
May b this can help

[syednayl]

So by the air induction tube you mean the tube running into the air filter box?

I will try and replace the PCV valve then and see what happens. Will take it out and rattle it around, any other reason why a seemingly fine PCV vale would not work as intended or do you recommend just changing the PCV valve and seeing what happens. I will also check any other area where unmetered air may be entering the car.

[syednayl]

Update: Took out the PCV, shook it around and rattled fine. Worked fine when blowing only allows air on one side to flow.

A pipe was not plugged in properly from the air induction tube, which I fixed. The Short Term Fuel Trim became better but not remotely enoug, now hovers between 15->10 but still not fine.

[Xulfiqar]

Run the car for 5 drive cycles, it will adjust, but it wont be perfect as you may have a lot of fuel in the engine oil too, from running rich for so long.