Mechanics

POOR MPG

2000 Chevrolet Cavalier • 4 cylinder FWD Automatic • 55,500 miles

Hi, I have a 2000 chevy cavalier and it all of a sudden started getting horrible gas mileage. I was getting 26mpg in the city. Now I have getting 17mpg highway and lesser than that in the city. I've checked for fuel and vacuum leaks, the spark plugs and wires, air filter, tire pressure and have found nothing wrong. The car runs great and doesnt smell like gas or idle rough. The car runs perfectly normal like it always did but before winter started it suddenly dropped. I have a flowmaster delta 40 muffler on it but I took my calculation of 26mpg after it was installed. I understand the winter takes away some fuel mileage but by how much I lost I think something else could be wrong with it. Can you help?
Avatar
Beat kid
February 14, 2011.



I'd use a gage and check fuel pressure. Also, check that the pressure doesn't drop like a rock when pump stops. If it drops quickly, check for leaking injector or pressure regulator.

JDL
Feb 14, 2011.
Ok thanks. I go to college for auto and I will to a test tomorrow bu I was wondering how to check the fuel pressure because cavalier don't have test ports for a gauge. Do I have to T into the fuel line? If so how

Tiny
Beat kid
Feb 14, 2011.
There is kit that modifies the fuel pressure gage with quick connect fittings, so that it will work with your vehicle. I didn't realize till just now, that you don't have a schrader valve. Yes, you have to tee into the supply line.

JDL
Feb 15, 2011.
Ok I tested the fuel pressure and its fine. I also looked for gas smells or leaks by the fuel injectors and there's nothing. I check my spark plugs again and I noticed they are turning white. What could be wrong?

Tiny
Beat kid
Feb 16, 2011.
Any applicable trouble codes? If you check codes yourself, at the least, you would need an obd2 code reader. Some of the national brand autostores used to check codes for free. Next, I'd want to see if system is running rich or lean and why?

JDL
Feb 16, 2011.
I used a scan tool in my auto class and nothing comes up for anything but for the BCM code u1000 pops up. Im just getting a little confused because the car is getting bad mpg, runs perfectly normal but the signs of the spark plugs are showing that it's running lean

Tiny
Beat kid
Feb 16, 2011.
What are the fuel trims doing, adding or subtracting? Do a compression test. I can't think of anything else, without looking at it.

JDL
Feb 17, 2011.
Ok I did a compression test and one on my cylinders had only 70 lbs of compression

Tiny
Beat kid
Feb 17, 2011.
The lowest cylinder reading should not be less than 70 percent of the highest. 100 psi minimum. Could rings or bad valves causing low compression.

JDL
Feb 17, 2011.
Ok do you think this could be the problem with my gas mileage? Also I noticed the head is covered in oil. And if the spark plugs are white, does that mean the car is running lean? If so would there be a problem with the o2 sensor?

Tiny
Beat kid
Feb 17, 2011.
Page 1 of 2