Aveo 1.2 SOHC- Hesitation, Poor Economy, low coolant, Random Negative STFT

[anandvsalunke]

Guys,

Need you help.
I have Aveo - Uva 1.2 SOHC (Indian Model) year 2008. The car has recently started hesitating and wont go past 80 kmph. It takes a good 60 sec to reach from 0-80 Kmph. Fuel Economy has also come down to around 10 kmpl (22 mpg). I had a coolant change last year and after three months from coolant change, it started giving the trouble.

Apart from that the coolant level has dropped from Max to somewhere middle of Man-Max markings on coolant reservoir. The coolant which was light green initially has turned dark green. I remember the earlier coolant was pink in color and i did ask the GM service guy as to why they changed to green color, but i was told they use a universal coolant nowadays.

When the car was taken to GM service center to diagnose this issue, they told me that my clutch assly needs be changed and they don't see any problem with engine, since there are no trouble codes set. I wasnt convinced with this diagnosis, since i had always driven my car carefully and 75000 km would be probably too early for the clutch to wear off. Besides, the clutch never slips.

I decided to diagnose myself. Spark tester shows good spark in all cylinders. Still i pulled off the spark plugs and changed them all. The old spark plugs appeared black & little wet. Next a compression test was done and all the cylinders passed, the readings were between 150-160 PSI. I went ahead and changed the fuel filter, Air filter, Engine Oil (5W30), Timing Belt and its tensioner as well.

Even after all this, its no better and still shows same symptoms. The fuel trims however reveals a different story. Every minute or so, the STFT goes way negative to 41 % and then comes back to zero. The LTFT values are around -7%. It looks like the ECU is able to correct the rich condition back within time and hence has not set any codes yet.

I did the injector resistance test after this and it passed. The injector were also taken to a professional shop, where they were cleaned and leak tested, and they all passed. Even after the injector cleaning, the car still hesitates & gives poor economy.

Now, more worrying thing is that it is slowly loosing coolant. But i don't find any traces of coolant outside or leaking hoses. I don't see a trace of coolant in oil either.

Anybody, can pl guide me right direction of diagnosis?

[anandvsalunke]

Don't we have engine experts here? please help.