[palsaumik]

Dear Members,

I own a Honda Brio i-Vtech Petrol EX-MT manual variant (2014 model) and has been running flawlessly all these years. Currently, it clocks around 58,000-odd kms on the odo.

Historically, I have been getting around 15-16kmpl in city drive and on highways it used to be around 18+kmpl. However, since the past few months I have seen that the mileage has dropped significantly to <10kmpl (tankful to tankful) for no apparent reason . Last weekend, I dropped off my car to Whitefield Honda in Bengaluru highlighting this issue and asked them to specifically:

1. Check and clean the fuel injectors and throttle body
2. Replace all the spark plugs
3. Replace existing synthetic engine oil with new synthetic oil (part of usual service schedule though)
4. Check clutch plates (if it needs replacement)
5. Clean fuel tank of any debris / deposits
6. Check fuel pump
7. Do wheel rotation and alignment
8. Check for anything / anywhere else that could be a potential problem area leading to low mileage

The car came out totally clean - there were no injector clogs, throttle body was quite clean, clutch plates are still good to run with for many more Kms, etc. They also checked the ECU / ECM for any error logs but couldnt find any either. Basically, they declared that the car is healthy and were baffled by the low mileage. Net-net, they couldnt pinpoint any other area which could lead to this issue.

I then went for another tankful-to-tankful test and I got 8.33kmpl - indicating a further drop in mileage .

As a last resort, I reached out to a local mechanic and they also couldnt effectively pinpoint to any specific issue once I told them the above items have already been checked.

Just for everyone's information,

1. There are no engine knocks - in cold or hot engine conditions
2. There is no black smoke on hard acceleration / revving
3. However, there is a considerable lag in acceleration in 2nd and 3rd gears since this issue came to my notice


Can the more experienced forum members here help in terms of where else I should look at for potential problem area(s)? Any advice to resolve this issue will be of great help.

Thanks,
Pal

[vishy76]

You seem to have crossed everything out on the fuel and spark front. But have you checked the MAF sensor and the O2 sensor?

A bad MAF sensor can cause the ECM to think there isn't enough air and dump fuel into the combustion chamber. A bad O2 sensor giving off erratic readings can also do the same. These two are very common reasons for bad fuel economy.

Take the car to a mechanic, hook up a scanner and access something called live data. As the name suggests, this will give you an option to monitor hundreds of engine parameters live including the MAF and O2 sensor readings and even the fuel trim data, indicating how the ECM is controlling the air fuel ratio. You can diagnose what exactly is causing extra fuel to make its way into the combustion chamber based on this data.

[Kosfactor]

Originally Posted by palsaumik

Can the more experienced forum members here help in terms of where else I should look at for potential problem area(s)? Any advice to resolve this issue will be of great help.

Fill up the tires to the required PSI, after that see if you can get down and push the vehicle easily on a flat ground. Handbrakes off and car in neutral of course.

[saket77]

Check for any leaks, tire air pressure, air filter as preliminary checks. Check for brake drag as well. Hope you’ll find the culprit.

Regards.

[Indian2003]

Originally Posted by palsaumik

Historically, I have been getting around 15-16kmpl in city drive and on highways it used to be around 18+kmpl. However, since the past few months I have seen that the mileage has dropped significantly to <10kmpl (tankful to tankful)

It could be a dirty air filter or binding brakes. It is not up to you to tell them what to do. The shop should look for the fault and fix it for you. There is also a temperature sensor in you intake manifold that regulates the amount of fuel for cold starts.

Just a few months ago I noticed my car drinking diesel and loosing power after about 20-30 kilometers of driving.. Everything was fine when I started the car but after a few kilometers, the car would loose power and brake by itself at tarffic lights. The car would not even roll down a hill.

The fault was with the front right caliper that got stuck when the brakes got hot. The brake rotor was blue on the outer edge.. I replaced both calipers and the problem was gone.

[longhorn]

Check if there is a leak in the fuel lines. Being petrol, it evaporates very quickly. Check for cuts or fraying on the hoses. It could be on the engine side or the tank side. Have both the ends checked.

[palsaumik]

Originally Posted by vishy76

But have you checked the MAF sensor and the O2 sensor?

Excellent points, Vishy. I never knew there were such sensors as well. Will have them checked immediately.

Originally Posted by Kosfactor

Fill up the tires to the required PSI, after that see if you can get down and push the vehicle easily on a flat ground. Handbrakes off and car in neutral of course.

Originally Posted by saket77

Check for any leaks, tire air pressure, air filter as preliminary checks. Check for brake drag as well. Hope you’ll find the culprit.

Originally Posted by Indian2003

It could be a dirty air filter or binding brakes. It is not up to you to tell them what to do. The shop should look for the fault and fix it for you. There is also a temperature sensor in you intake manifold that regulates the amount of fuel for cold starts.

Just a few months ago I noticed my car drinking diesel and loosing power after about 20-30 kilometers of driving.. Everything was fine when I started the car but after a few kilometers, the car would loose power and brake by itself at tarffic lights. The car would not even roll down a hill.

The fault was with the front right caliper that got stuck when the brakes got hot. The brake rotor was blue on the outer edge.. I replaced both calipers and the problem was gone.

Checked on these today morning and it rolls freely. No resistance there. Air filters are brand new, so no suspects here.

Originally Posted by longhorn

Check if there is a leak in the fuel lines. Being petrol, it evaporates very quickly. Check for cuts or fraying on the hoses. It could be on the engine side or the tank side. Have both the ends checked.

Thanks, I will have it checked and replaced as preventive maintenance.

[pkulkarni.2106]

While you're at it, you can also ask them to check the throttle position sensor.
I've read it a few times that a bad TPS can cause both - hesitation during acceleration and drastic drop in FE.

Thanks!

Originally Posted by palsaumik

Excellent points, Vishy. I never knew there were such sensors as well. Will have them checked immediately.

[2000rpm]

Originally Posted by palsaumik

g around 15-16kmpl in city drive and on highways it used to be around 18+kmpl.

You were getting 16 KMPL in Bangalore! I think there was something wrong earlier with the Instrument cluster and now it has gotten corrected

On a serious note, Let me give a few non technical ideas, as I think a thorough technical diagnosis has been completed

1. Is there more than one driver driving the car, that sometimes affects the mileage??
2. Possibility of Petrol Theft in parking??
3. Have you started filling the petrol from a new pump, or has the management of an exiting pump changed? Fraudulent Petrol Pump?

[AntPaul]

Have the usage pattern changed post pandemic? Efficiency will be less for first few kilometers on a cold engine. If you use the car consistently for short drives, you could see sub 10 kmpl FE figures. This has been my experience.

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.

[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.

[palsaumik]

Originally Posted by pkulkarni.2106

While you're at it, you can also ask them to check the throttle position sensor. I've read it a few times that a bad TPS can cause both - hesitation during acceleration and drastic drop in FE.

Many thanks. I am not sure how they do it but will definitely have this checked as well.

Originally Posted by 2000rpm

You were getting 16 KMPL in Bangalore! I think there was something wrong earlier with the Instrument cluster and now it has gotten corrected

On a serious note, Let me give a few non technical ideas, as I think a thorough technical diagnosis has been completed

1. Is there more than one driver driving the car, that sometimes affects the mileage??
2. Possibility of Petrol Theft in parking??
3. Have you started filling the petrol from a new pump, or has the management of an exiting pump changed? Fraudulent Petrol Pump?

Excellent points, but:
1. No, I am the sole driver in the family
2. No, since we have a secured basement parking
3. Well, the low mileage issue has been over some time now and re-fueling has been from random but good stations within the city. With multiple tank-to-tank tests, I doubt if it relates to a specific fuel station selling spurious fuel

Originally Posted by AntPaul

Have the usage pattern changed post pandemic? Efficiency will be less for first few kilometers on a cold engine. If you use the car consistently for short drives, you could see sub 10 kmpl FE figures. This has been my experience.

Well, the drives have been both for short runs as well as long highway runs (as an escapade from boredom). Under all conditions, I got <10kmpl.

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.

Pretty interesting, I will check on that as well over the weekend and update. Thanks for the pointer.

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 am also inclined to think that O2 sensor could be the issue here. I have noted it in my list of checkpoints and shall circle back pretty soon.

Truly appreciate everyone's time, thoughts and advice here.

[d2krish]

Do you have ABS in your car? If so, and if the sensors are shorted, it might engage the brakes at its whim and cause drop in acceleration to moderate to heavy drop in mileage. O2 sensor also might be another culprit as already identified. Check that too.

[palsaumik]

Originally Posted by d2krish

Do you have ABS in your car? If so, and if the sensors are shorted, it might engage the brakes at its whim and cause drop in acceleration to moderate to heavy drop in mileage. O2 sensor also might be another culprit as already identified. Check that too.

Thanks, Krish. No ABS or EBD in my 2014 model. For that matter, it does not have airbags even. Car is pretty barebones in terms of such features.

[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.

Brake Booster: When I had similar issue in my Beat, it turned out to be a faulty brake booster. Again air intake pressure issue. My brakes were dragging. After driving for 10km+ on open roads, where you don't have to use the brakes much, touch and check the temperature of wheels and brake rotors. They should stay cool if the brakes aren't dragging.

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.
I normally keep about 5PSI higher in front wheels of the Beat and 0-2 PSI lower in rear wheels to compensate for the engine weight and maintain same contact patch on all wheels. Wear and tear remains flat. No extra wear on the centre belt.

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.

Less Usage: Even with my Beat, which is diesel (oil), if I'm using the car very less, the FE drops considerably. When most of my driving is with a warm engine (as in emptying the tank in like a week and 50km+ per drive) that's when I get the best FE. When my car is only doing 5-10km grocery runs and each tank full is lasting me 3-4 months, the tank-full-to-tank-full calculation shows about 20% drop. But, I'm fine with that as overall, it's still cheaper because of net less expense on fuel.

Final Tip: Prioritize the suspects and troubleshoot 1 thing at a time. So you know exactly what is the culprit.