[Mr. Nobody]

Background of my car:
Grand i10 Petrol - 72k Kms old

Service History:
Last year clutch kit was changed and mileage was good post the replacement and was easily around 14 in city.

Now 2 months back i got a general service done and they added a value add job of "combustion chamber cleaning". Now after this service mileage has fallen big time to around under 10 in city.

Post this drop in efficiency i have changed all spark plugs to Iridium ones, cleaned the MAP sensor recently, check spark plug wires for resistance, throttle body checked(it was already clean), used a Liqui moly injection cleaner and also added a Liqui moly engine oil friction reducer but mileage is still barely 10 ( very slight improvement). I have the Torque App and i have used it to check the following data points:

1. Long term fuel trim values - Has been under 5%
2. Car seems to have a narrow band O2 sensor and hence no A/F ratio readings. Car goes to open loop on hard throttle.
3. O2 sensor 1 shows standard fluctuating readings which i think is normal.
4. O2 sensor 2 shows high readings meaning engine is running rich which matches the fuel efficiency issue.
5. Coolant temperature sensor shows 90 within 10 minutes of drive showing its working ok.
5. No issues in acceleration and car drives like new except this mileage drop.

What could the issue be ? I feel the combustion chamber clean has caused debris to deposit on O2 sensors or the CAT causing bad values. Or can it be some sort of a fuel leak somewhere?

[Bsilver]

Originally Posted by Mr. Nobody

4. O2 sensor 2 shows high readings meaning engine is running rich which matches the fuel efficiency issue.

If you can, pull out the data of the fuel system in the the respected app which you are using, then see if the High Pressure Fuel pump is reaching the specified value which the ECU is requesting. If everything is good till the HPFP, then check the rail pressures. These are one of the ways in which you can eliminate the chances that it is a fuel issue. Usually in the cleaning process there might be 2 ways, directly introducing the cleaning agent in the intake, or introducing the agent direct to the cylinder, then they pressurize using a tool, which forces the cleaning agent to go down the rings of the piston at where there is carbon build up. But then usually if the process is not proper, or you have a really high mileage engine, then there are chances that due to this process, the piston rings are not binding to the cylinders, resulting in compression losses, which will directly reduce fuel economy. But since you have told you do not have loss of power, looks unlikely of a compression issue, but worthy of a look as well. But on a 72k driven car, why exactly did you get a combustion chamber clean? The mileage is not that high as per my personal belief. You can try the above and check out the results. Happy Motoring!

[Jeroen]

On most cars all the downstream O2 sensor does is monitor the functioning of the catalytic convertor. So it has no effect on engine performance at all. Neither does the catalytic convertor has an effect on your engine performance. Unless it is blocked, which would not only affect mileage but usually causes performance issues as well.

The upstream O2 sensor is the one that controls the mixture.
There is a wide misunderstanding about running rich. Although it does decrease mileage, it is barely noticeable in practice. Unless you see black smoke belching from your exhaust it is unlikely that a rich running condition is causing a major shift in fuel mileage.

Read about my “running rich” issues on my Alfa Spider in my fiddling with car thread.

The Upstream O2 sensor should not be fluctuating all that much. Unless you are constantly blipping the pedal. It should be pretty stable during acceleration, idle and constant speed. As a rule of thumb the O2 value follows the movement of your throttle pedal. No movement it must become stable.

If you have a problem with either the up- or downstream O2 sensors that almost always leads to a check engine light as well.

I would start with the basics first. Check the air filter, check the spark plugs, leads. Low fuel pressures tend to cause lean conditions, not rich.

You might want to try and put a good proper OBD analyser on your engine as well. I don’t trust these apps at all. Even though your check engine light is off (at least I assume it is off) that doesn’t mean there are no error codes. You need an OBD reader that can read manufacturer and model specific codes. Without a proper error code check all bets are off.

As you mentioned this all started afterwards of the cleaning, I would still do a compression test. A leaking valve or problem with the piston rings can cause mileage issues of course. You might not notice it in engine performance so much. So best check as well.

Good luck

Jeroen

[Mr. Nobody]

Originally Posted by Jeroen

Good luck

Jeroen

The upstream O2 sensor does show rapid fluctuating readings in a narrow band O2 sensor. Which i checked everywhere is normal. Same can be seen in the first screenshot in the top right graph. OBD2 readers are straightforward and the paid app by Torque is very well trusted universally. There are no error codes or CEL though I will still get another check by another tool and do a compression test this weekend.

I could not find the posts you are referring to, can you share a link?

Originally Posted by Bsilver

If you can, pull out the data of the fuel system in the the respected app which you are using, then see if the High Pressure Fuel pump is reaching the specified value which the ECU is requesting. If everything is good till the HPFP, then check the rail pressures. These are one of the ways in which you can eliminate the chances that it is a fuel issue.
!

The app does not show Fuel pressure values. So either my car does not have that sensor or app does not support it. Will get it checked soon along with the compression test. I was told it's a mild maintenance step and i agreed which i logically should never have as i had already used Liqui moly cleaners and was having no issues as such.

[Jeroen]

Originally Posted by Mr. Nobody

The upstream O2 sensor does show rapid fluctuating readings in a narrow band O2 sensor. Which i checked everywhere is normal.

OBD2 readers are straightforward and the paid app by Torque is very well trusted universally..

Awesome! If you believe all of that I have a bridge for sale you should have a look at!

I must be really dim buying all this hugely expensive car diagnostic equipment.

Jeroen

[Mr. Nobody]

Originally Posted by Jeroen

Awesome! If you believe all of that I have a bridge for sale you should have a look at!

I must be really dim buying all this hugely expensive car diagnostic equipment.

Jeroen

I'm merely mentioning information taken from a big automotive company.
https://www.ngk.com.au/technical_inf...20milliseconds

Regarding being dim i have no idea but i guess we now have labs to check that.

[Jeroen]

Originally Posted by Mr. Nobody

I'm merely mentioning information taken from a big automotive company.

As with lots of stuff out there on the internet it is very generic.
Lots of Internets will tell you about this O2 sensor voltage flipping. Those souls wanting to impress you will mention the generic properties of such sensor make it in practice a on/off switch. Which is not necessarily untrue, but it isn’t always true either. It certainly isn’t necessarily true when there is something wrong with the system.

I will never ever hook some app to my car. If there is one thing that is likely to damage an ECU it is cheapo app. The folks that deal with real ECU problems (which are extremely rare) will tell you that a fair share of the ECU problems is due to these OBD apps.

Yes, in principle OBD is simple. But that doesn’t mean it easily understood. If you want to rely on live OBD measurements you really need to understand how the app works internally. Because OBD data is never raw data. It has always been manipulated, composed and or derived from various sources.

Again, that doesn’t always need to be a problem. But if you are facing tricky issues, such as you do (no error codes, but massive change in fuel efficiency) it pays to be extra cautious a d understand what it is the OBD reader is telling you.

If you get your hands on a true OBD reader make sure it can read manufacturer and your model specific codes. There are far more manufacturers and model error codes out there than the generic OBD codes.

Back to the generic information in your link, it mentions you should check it with an oscilloscope. Not an OBD live data feed. For all the reasons afore mentioned. Any half decent mechanic who needs to trouble shoot car electronics would have one. I have one.

The big difference, it means you would measure directly on the sensor. So you are actually measuring raw data, the voltage on the sensor. You cut out all the stuff the ECU and other components might do with the signal.

I have no idea what your app measures, but I can tell you one hundred percent for sure it’s not the sensor voltage. It is something derived. Also, you might want to check the sample rate of your app. Does it get anywhere close to what the oscilloscope has as a sample rate? If so, how do you know? If we don’t know or the sample rate is too low what and we don’t know how the data in the app is derived, how can we draw conclussions?

Here a link to a part of the problem with my Spider.

https://www.team-bhp.com/forum/diy-d...ml#post5783697 (My Car Hobby: Jaguar XJR, Mercedes W123, Alfa Romeo Spider, Jeep Cherokee & Mini One)

If you scroll upwards you will find some more posts about this particular problem of over fueling which is even worse than just running rich.

We have it hooked up to a number of analysers. We have a direct O2 measurement in the exhaust. A direct 02 sensor voltage measurement and an ongoing OBD2 live measurement. (Which lags behind). And a bunch of other measurements.

The Spider has a mainstream (I think it is a Bosch) narrow band upstream O2 sensor installed.

Question: how much fluctuation of the voltage of the narrow band sensor do you think we found?

Good luck with your trouble shooting!

As I mentioned before. With these sort of issues always check the basics first. No (manufacturer/model/generic) error codes. Check all the obvious stuff, from tire pressure to simple stuff as spark plugs, inlet air filter, spark leads, coils, fuel pressure, valve clearance and so on. Don’t forget to check the health of your battery and ensure clean terminals everywhere. The weirdest of problems materialize in cars electronics due to low voltage. Either a battery on its way out, a corroded terminal or a combination.

Without having certainty the basics are ok, I don’t think it makes sense trying to drill into various more complex components. Just my opinion and experience.

I don’t want to confuse the issue or worry you even further but a recent experience with the upstream O2 sensor on my Jaguar showed that even my very expensive OBD scanner can get it wrong. Also some information on the various generic/manufacturing codes are discussed

If you want to be a bit more confident on the state of the 02 sensors, get a multimeter, find the values in the technical documentation and measure the resistance.

https://www.team-bhp.com/forum/diy-d...ml#post5735926 (My Car Hobby: Jaguar XJR, Mercedes W123, Alfa Romeo Spider, Jeep Cherokee & Mini One)

Jeroen

[Mr. Nobody]

Originally Posted by Jeroen

...

Good luck with your trouble shooting!

As I mentioned before. With these sort of issues always check the basics first. No (manufacturer/model/generic) error codes. Check all the obvious stuff, from tire pressure to simple stuff as spark plugs, inlet air filter, spark leads, coils, fuel pressure, valve clearance and so on. Don’t forget to check the health of your battery and ensure clean terminals everywhere. The weirdest of problems materialize in cars electronics due to low voltage. Either a battery on its way out, a corroded terminal or a combination.

Without having certainty the basics are ok, I don’t think it makes sense trying to drill into various more complex components. Just my opinion and experience.

I don’t want to confuse the issue or worry you even further but a recent experience with the upstream O2 sensor on my Jaguar showed that even my very expensive OBD scanner can get it wrong. Also some information on the various generic/manufacturing codes are discussed

If you want to be a bit more confident on the state of the 02 sensors, get a multimeter, find the values in the technical documentation and measure the resistance.

https://www.team-bhp.com/forum/diy-d...ml#post5735926 (My Car Hobby: Jaguar XJR, Mercedes W123, Alfa Romeo Spider, Jeep Cherokee & Mini One)

Jeroen

Interestingly i did a few 0-100 runs to check the performance which came out excellent and the fuel economy seems to have gotten better a bit which needs to be further re-checked manually. The engine still seems to run rich though.

Yes most of basics you have mentioned i have personally checked and fixed. The things left for checking are valve clearance/compression test, fuel pressure, injector leaks and maybe a upstream O2 sensor replace if cleaning it is not recommended and its available in a reasonable cost.

[Jeroen]

Originally Posted by Mr. Nobody

. The engine still seems to run rich though.

Why, what symptoms, measurements

Originally Posted by Mr. Nobody

Yes most of basics you have mentioned i have personally checked and fixed. The things left for checking are valve clearance/compression test, fuel pressure, injector leaks and maybe a upstream O2 sensor replace if cleaning it is not recommended and its available in a reasonable cost.

I would not replace the O2 sensor unless it’s faulty. Without an OBD error code very unlikely. As I mentioned, easy to check with a multimeter.

Good luck

Jeroen

[venukrithish]

Check for black smoke. That's your indication if it's running rich.

[Jeroen]

Originally Posted by venukrithish

Check for black smoke. That's your indication if it's running rich.

It's an indication, but not a certainty it is running rich. It indicates an incorrect combustion process and that could be due to numerous issues. From problems with injectors, air leaks (yes they can also cause rich conditions on some engines), incorrect valve clearances, problems with piston (scraper) rings, failed catalytic convertors etc etc.

Looking for black smoke on a modern car is a bit of a carryover from the olden days before catalytic convertors and carburettors.

It helps to check if you see black smoke under acceleration or under "off the throttle" conditions. The latter almost certainly indicates problems with valve stem seals and or piston rings and or some kind of blow back/high pressure in the crank case. (e.g. blocked crank case ventilation or so)

When you come off the throttle, no fuel is injected, so there is no combustion. All black smoke you might see is lub oil burning up in the hot cylinders, exhaust, cat and so on.

Jeroen