I have a 1999 catera and I have noticed that over the past month or so the gas mileage is getting really bad. I had it into the garage and they changed the air filter and plugs and it still is bad. I go 50 to 60 klms on a 1/2 a tank of gas and it cost me $32 to fill it up again. Can anyone give me any idea's what else they sholud check. Any help would be greatly appreciated.
Welcome to the club of Low MPG. My cat can go only 240 miles on regular gas . And like 190 on premium. And I'm not flying around. Keeping my idle up to 3000rmp.
OEM New spark plugs.
Air filter, fuel filter
Injectors hand cleaning and multiple time cleaners to the fuel tank was add + seafoam was preformed few times to.
what you might try is start the car and have someone run the RPM,s up, at the same time go to exhaust pipe and smell the exhaust, if really is strong than your burning rich, (more fuel than needed) The most common problem to this is a bad MAF, I took mine out and bought MAF cleaner, clean it and put it back, took off all the connection to it and but them back on, it work for me, might for you,
Pass month was monitoring my mpg:
2000 Cadillac Caters Sport with 153k miles, tire pressure was monitoring. Had full trunk of my tools, include prof. heavy jack. Newer air and fuel filter. OEM spark plug with approx. 20k on them. Engine oil Castrol GTX 5w-30 had approx. 3k of use when I started my mpg monitoring. Car was treated with Lucas and Seafoam frequently in a pass. During this time had no passengers and only me drove the vehicle.
Regular 87 - 16 mpg
Premium 93 - 13.1 mpg
Both time used Costco gas. Vehicle was driven in city only, in general keeped my foot on up to 3000rpm. But some time had to reached to 5000. I'm not crazy driver.
I did saw the differents between 87 and 93 gas. Premium gave me better power and kind of stable. But It was not worst to lose 50 miles of driveble distance by using premium 93 gas....
Well in my 2001 catera sport black i been having suspicions of the coolant bridge sensors theres two sensors on the coolant bridge.One is a single wire plugged on top of it and this sensor gives you the reading on your dash.the other one is a coolant temp sensor that tells your ECU(electronic control module) when it has reached closed loop so if that sensor is faulty youre runnig open loop for a longer period of time ,witch will kill youre gas mileage try looking into those sensors there only like 12$ each and try cleaning the ccv(cranck case ventilator )