[vtecblast]

It has been mentioned quite alot on the forum but O2 sensor is the only thing at fault here.
Additionally, get your intake manifold cleaned and did you get the fuel filter changed?

[trupian88]

Like mentioned in the earlier threads here, of the O2 sensor checks out please get a compression check done. A faulty piston/oil ring might be to blame. Although that should turn up in your emission checks, but it is worth a try. Please call up the service center to find out if they have the equipment...

[pkulkarni.2106]

Since O2 sensor is one of the vital sensors in the system, wouldn't a bad O2 sensor cause far more visible symptoms and easily be caught in the PUC readings?
Plus, I'd expect it to light up the CEL on the dashboard.

[Adam]

I have been facing similar issues on my Polo, I was getting around 9-10 Kmpl in bumper to bumper traffic and eventually it dropped to 6 Kmpl, I cleaned my Mass Airflow sensor and Throttle body and it got back to normal.

So I suggest you to check MAF Sensor and O2 Sensor, normally these sensors throw a check engine light and Error code if failed also you may feel jerkiness and uneven acceleration at times, but an abnormal value sometime may not show any error code, so as a fellow bhpian suggested its good to check the live value with a competent FNG. Also check out your TPS-Throttle position sensor, though its bit rare failure point

[amitjha086]

Just a query: Have they been filling the same amount of petrol into the tank that is displayed on the fuel dispenser?

[palsaumik]

OK, so I spent a long time at Honda Service today and had them do detailed diagnostics, road tests, brake caliper checks, etc. And I am sad to say - that I am more confused with the car coming clean from any issues.

Originally Posted by AntPaul

An easy way to check if MAF and O2 sensors are good is to get an emission test done on a warm engine and check of O2 and CO levels. CO levels should be really low. It will be ideal if you have any of your older emission test results with you which was done at the same place. It might give an indication if the engine is running too rich or too lean.

Got the PUC tests done and here are the old vs. new test results. I am not able to figure out any glaring differences. Any thoughts here?

Originally Posted by kamilharis

Check the O2 sensors. We had a similar issue in Honda City ZX (Dolphin) and the culprit was a faulty O2 sensor. The O2 sensor is a bit costly too.

I got a detailed Diagnostics Done today and looks like the O2 sensors are working just fine. No red flags. Detailed report attached below.

Originally Posted by MaheshY1

MAF: I experienced sudden acceleration and FE issue together in my Nano. After a lot of back and forth with Tata ASS, they found mass air flow sensor. The air intake pipe had gaps and it was skipping the air filter and breathing directly.

Tyres & Wheels: The other issue I have faced was just simple tyre pressure and alignment. Together, they dropped my FE by 30%. After 2 tank fulls, I knew that this wasn't a fluke, and the problem was there. Pressure and alignment were way off.


Leaks/Vaporization: Check for leaks. Petrol is spirit. So, any leak even above the fluid level will affect FE as fuel evaporates.

Fuel Pump Reading: Try a different gas station. Maybe a COCO type to see if that affects.

Honda SA said 2014 Brio doesn't have MAF sensor. I still doubt his statement but if someone here can confirm, it will be great. The air pipes in my case were checked and found to be well fastened and secured. Tyre rotation and alignment was done 2 weeks ago. Even after that, the fuel efficiency issue continues. No fuel leakage found whatsoever though.

Originally Posted by trupian88

Like mentioned in the earlier threads here, of the O2 sensor checks out please get a compression check done. A faulty piston/oil ring might be to blame. Although that should turn up in your emission checks, but it is worth a try. Please call up the service center to find out if they have the equipment...

This one is probably the only item pending. Will have it done shortly.

Originally Posted by pkulkarni.2106

Since O2 sensor is one of the vital sensors in the system, wouldn't a bad O2 sensor cause far more visible symptoms and easily be caught in the PUC readings?
Plus, I'd expect it to light up the CEL on the dashboard.

Totally agree. As of now, CEL has never lit up. I mentioned your pointer to the guy who was running the diagnostics today by hooking up a laptop running Honda Diagnostic Service software. He too agreed that while CEL will light up, many a times it doesn't and he checked for any hidden failure indicators as well. Nothing could be found

Originally Posted by Adam

I have been facing similar issues on my Polo, I was getting around 9-10 Kmpl in bumper to bumper traffic and eventually it dropped to 6 Kmpl, I cleaned my Mass Airflow sensor and Throttle body and it got back to normal.

So I suggest you to check MAF Sensor and O2 Sensor, normally these sensors throw a check engine light and Error code if failed also you may feel jerkiness and uneven acceleration at times, but an abnormal value sometime may not show any error code, so as a fellow bhpian suggested its good to check the live value with a competent FNG. Also check out your TPS-Throttle position sensor, though its bit rare failure point

Honda SA said my car doesnt have MAF (I am not sure if he's true about this). Fuel injectors and throttle body were cleaned 2 weeks back and were found to be OK with barely any clogs / deposits therein. No engine knocks, just loss of acceleration in 2nd and 3rd gears.


I am now at my wits end! Any last nook-and-corner I should look at?

[stallmaster]

I may be grasping at straws here, but have you tried disconnecting the battery for 15mins and reconnecting? That should recalibrate the base sensor readings in your ECU. Sometimes that fixes ghost issues in a lot of cars.

[CaptainBrijesh]

Originally Posted by palsaumik

Got the PUC tests done and here are the old vs. new test results. I am not able to figure out any glaring differences. Any thoughts here?

Oxygen readings in your PUC are quite high. if you have paid attention, then you must have noticed that Oxygen (O2) readings have increased by 2-3% in latest PUC from Old PUC readings, which itself was quite high. O2 Sensor seems to be the most probable culprit here.

Also, check for any leakage in Exhaust system. Somewhere i read that on most of the cars which are more than 3 years old, the most probable reason of decrease in fuel efficiency was leakage in exhaust system. Although this cannot cause this drastic fuel efficiency drop but there is not harm in checking it.

Hope it helps!

[JP_800]

Hey Paul,
From your old and new PUC, the CO & HC levels have increased by abnormal levels over a period of just 5 months. CO & HC are formed due to incomplete combustion, ie when fuel is burnt partially. This can happen when there is lesser air or more fuel. It can be either that the air pathway is restricted , causing the Engine management system to dump more fuel to compensate, or due to a faulty O2 sensor. In the live data reading, it just mentions that the O2 sensors are ON, not the values. I would suggest to check the air pathway once again , starting from air filter, all the way up to the Throttle valve. There is a function called actuator test for check whether the throttle body is working or not, in the OBS scanner.

If air pathway is fine, then O2 sensors might be the culprit

[rohanhsaraf]

You should get your car scanned with a obd scanner, in my opinion it's the oxygen sensor. Facing same issue with my Chevrolet spark it's also delivering fuel economy of 8-9 kmpl. Mostly O2 sensor ranges from 2-10 k, it depends upon vehicle.

[Adam]

Originally Posted by palsaumik

OK, so I spent a long time at Honda Service today and had them do detailed diagnostics, road tests, brake caliper checks, etc. And I am sad to say - that I am more confused with the car coming clean from any issues.



Honda SA said my car doesnt have MAF (I am not sure if he's true about this). Fuel injectors and throttle body were cleaned 2 weeks back and were found to be OK with barely any clogs / deposits therein. No engine knocks, just loss of acceleration in 2nd and 3rd gears.


I am now at my wits end! Any last nook-and-corner I should look at?

Actually the SA might be right too, as not every car have both MAP and MAF Sensors, and as per the detailed report share by you , there is MAP sensor in your car, which is Manifold Absolute Pressure. Both MAP and MAF Sensor failure will have similar symptoms. MAP Sensor failure will cause typically following problems.

• Rich Air fuel ratio/ Lean Air Fuel ratio
• Check Engine light
• Misfire
• Hesitation to accelerate or uneven acceleration

If you Car is running rich you may get some strong petrol smell especially at idle, if you car run lean you may experience some stalling. Do check it once, as seen in your report MAP sensor is functioning, not quite so sure about the optimum value for MAP , do check once with SA and get his opinion.

[knshailender]

Talking about O2 sensor, Honda is known to charge exorbitant price to replace the O2 sensor. If you plan on replacing it, I suggest sourcing it yourself and changing it at a reliable mechanic shop.
If I'm not wrong Honda uses Denso sensors. Get the part number and order it on Amazon.

[bj96]

Originally Posted by palsaumik

...
Honda SA said 2014 Brio doesn't have MAF sensor. I still doubt his statement but if someone here can confirm...

Mine is Feb'13. It doesn't have MAF. I have recently switched (~2000 kms ago) to (self procured) full synthetic 5w30 Shell Helix in a FNG. Seeing decent in city mileage gain from ~12 kml average to ~15 kml now. If you have not already done, try also changing your regular fuel bunk and maybe a higher octane petrol refill to verify fuel adulteration is not a issue here.

-BJ

[palsaumik]

Well, a hearty THANKS to all BHPians here - who took the time and effort to suggest where the probable issues could be. And I am glad to say that the fuel efficiency issue HAS BEEN RESOLVED!

The O2 sensors were the prime culprit in here. One weekend, I got both the sensors replaced replaced at Magnum Honda Kanakapura Road. Immediately thereafter, I could immediately observe a marked difference in acceleration and overall power delivery. The engine now responds superbly to even minimal throttle inputs. I cant recall when it was so agile even since the delivery of this car in 2014.

Last weekend, took it out for a mileage test to Bandipur and it returned an efficiency of 19.1 KMPL tank-to-tank. On the instrument cluster, it was showing 20.3 KMPL. The engine whirring noise is gone too and sounds very smooth and settled. Surprisingly, no Engine Check Light ever popped up.

Here's how the old sensors look like:



This car is a keeper for long again!

[Crankpin]

That's good! What did the pair of o2 sensors cost you? Did you change them yourself?