Salam Guyses, here is a little issue of mine that I been facing recently.
The car in question is a Corolla 2nZ-Fe 1.3L Stock with 180k km on the ODO. It has been on CNG since Day 1 (literally). The CNG installation was really sweet and I enjoyed driving it equally on petrol and CNG both. I got its NG kit FULLY serviced a month back, and the performance was simply excellent.
It returned me excellent mileages and low gear performance on CNG until about a fornight back, I sent it to workshop for its periodic maintenance.
The spark plugs were changed, throttle body was thoroughly cleaned, certain belts changed, transmission fluid changed, brakes serviced and overhauled completely, some suspension work etc etc.
Workshop work was of high quality, each and every nut that was used was OEM Genuine Toyota. Nothing from the local market was bought, everything was directly from Toyota Indus motors. But the day I got my car back, CNG was off, so I drove it on petrol, I simply was in love with it even more after the maintenance because it felt just like brand new back in May 2008.
On the other hand When I got CNG filled, the performance had significantly gone down. The car used to stall at low rpms, esp with AC and a few people on board. While on petrol the drive was as effortless as it could ever be.
Therefore I took it to a number of mechanics in Rawalpindi, some very well known for their expertise in CNG adjustment. All of them tried very hard and failed. Some just fiddled with the T-bolt, some tried increasing idle rpms, some opened the tappet cover, some touched the advancers but only one word awaited them: Failure. Therefore I brought it home with a heavy heart and popped the hood.
Had a few looks here n there, checked the venturi etc and then set off to adjusting the gas. I adjusted it on rock hard 3300rpms. After that, the car just felt "MAMAMAMAMIIIAAAAAA" on CNG!
I mean awesome pick, awesome performance and what you guys won't believe is it continuously returned me 180-215 kms in single fils worth 650 Rs (~8.5kg) with full AC three times in a ROW! Wow, I loved it.
But then, CNG ki loadshedding ho gai, and it was driven like 450-500kms on petrol. Then yesterday when I got CNG again, the performance had returned to where it was before my adjustment. Bogging, low power, close to zero throttle response, with AC was even worst! Mileage dropped significantly, I mean WTF, 40kms main 300 ki CNG phakk gai! :S
So I searched here and found out a lot about venturis and air blockage but no solution to my problem.
I opened up the whole intake of the car and found close to "no air blockage" whatsoever.
The CNG goes in thru a slim slit type cut pipe sticking in the middle and there is just a metallic ring around it, which is there to support the rubber intake pipe I think.
But it offers no resistance to air since its wide open.
I am not sure if it was like that since Day 1 or not but its like that now. But a serious change I noticed in the car was awesome petrol mileage.\It gave me purely 13-14kpl mileage with a moderate to heavy foot and with FULL time AC on, in local and on highway, both! Earlier than the tuning, I don't remember it returning more than 10kpl at the max.
Now here are the queries: