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-   -   Chevrolet Optra, drinking petrol- Help! (https://www.team-bhp.com/forum/technical-stuff/79277-chevrolet-optra-drinking-petrol-help.html)

My Chevrolet Optra just returned a fuel efficiency of 3 km/litre with a tankfull - that's probably what a Camaro would have returned (maybe higher).

Little bit of history:

- The 1.8 litre petrol engine usually gives 8 km/litre with AC on.

- Last week, I had taken the car to the service center because the AC compressor would stop working after 10 minutes of operation.

- The service center returned the car back after repairing the AC. Apparently, there was a problem with sensor, and it had to be re-programmed (or something like that).

- The AC is fine, the car's road performance is normal, the gear ratios are normal - but the car is returning 3 km/litre.

Problem Elimination Steps Taken:

- To check whether it was a quality of fuel problem, I filled up 10 litres from another petrol pump (Shell) - but the fuel guage needle is again falling like a rock.

- I checked under the car in the garage - there is no drip, drip fuel leakage.

- With the engine running, I checked under the body - no fuel leakage again.


Today, I took my car to the service station. I got a call back today saying they haven't been able to figure out the solution for the problem for sure. All the ECU and the electronic settings are normal apparently. But they have replaced all four plugs, saying it was worn out. They are not charging money for the spark plugs (because their solution is basically trial and error), and have asked me to check the fuel efficiency and report back. I'm picking up the car tomorrow.

My best guess is that they messed up with the electronics/electrics while trying to set the right AC sensor "programming".

Any guesses?

Have you checked your tire pressure yet?

Please check the pollution levels and then get back to the forum with the readings. If its within limits then its a petrol fume leak. Happy hunting. If its not a petrol fume leak then check for rolling resistance.

All four tyres are perfectly inflated.

There is no excessive smoke coming out of tailpipe. But after I get my car back tomorrow, I will get the pollution check done. This is a good idea - if there is any excess CO2 levels, then it probably means the engine is not buring the fuel efficiently.

An O2 sensor malfunction maybe? Engine sensing more air than is actually going in and reacting by injecting more fuel? Emission check might give an indication.

Am not really technical - but something like this was once investigated for my car.

You cannot know your FE by just filling ten litres. Fill the tank, drive some 200 km and fill it again. The difference will give your true consumption.
Try it, you'll be surprised that the FE will be close to your normal figure.

get the fuel tank cleaned and all the fuel lines checled, including all the hosepipes and of course, get the AC system checked again, the compressor should not put load on the engine.

- Possible O2 Sensor malfunction
- Get gas tank cleaned
- Check AC system again (This is a good one - might be the issue)

Thanks. Will get all this done next time, if there is no improvement in FE (after the spark plug change). All the fuel lines have been checked by the service center - they seem to be OK apparently.

I'm going to get my Camaro from the service station now.

In the current state, the car won't run for 200km on a full tank - 150km max. Plus, I don't want to burn Rs. 2,500 for a tankful of petrol. So after getting the car, I will run it till the red light glows, fill 10 litres and then see when the red light comes back again.

Which service center do you go to?

Frontline Automobiles (near RV College of Engg, Mysore Road). I've been very happy with their service (before this incident happened, of course) - many times better than Sundaram Motors. Kropex is too far from home.

That's must be from your personal experience. :)
Any way just let me know after you get your car out. If that issue is still there, we can do something surely.

Get the fuel guage sensor checked. It might have gone wrong. 3km/ltr is unheard of.

Shan2nu

I just got back the car from the service center. Along with changing the spark plugs, they have also cleaned the IAT (Intake Air Temperature) sensor apparently.

My service advisor told me that it could not be an O2 sensor problem - because if something goes wrong with the O2 sensor, the "engine light" will start glowing on the dashboard. Also, in the morning, he has asked to switch ON the engine and block the silensor for a second with my palm. If I see water on my palm, apparently it means the fuel/air mixture is correct.

The service station is 9 km from home, and going by the pace at which the fuel gauge needle was falling, I don't think the problem has been rectified. But will wait for a couple of days to confirm.


Yeah, I have all the bad luck when it comes to car servicing. Because of Sundaram's negligence, the car broke down twice on two different occasions - immediately after getting the car back from servicing. The reason for the breakdown was something as silly as not plugging in the wires/fuel lines into the sockets properly.

When you go to Sundaram, do you insist that your car should be taken care of by a particular service advisor? If yes, give me his name. The reason for different experiences at the same dealership is PEOPLE. Although all dealerships have certain processes, not everybody follows them correctly.

Oh, I hadn't thought about this. Maybe I'll do a full tank to full tank - if 50 plus litres goes in, that means the fuel guage sensor is OK.

The issue has been resolved. Looks like IAT sensor cleaning and spark plug replacement did the trick. I got my Optra back.

great to see the problem solved. so now you are on new spark plugs ? I wonder how come this problem arose after your AC servicing !