My 93 Corolla is Getting Poor Gas Mileage

[Lois]

I've had my 93 corolla since 1999. It runs great, although it's been getting very bad gas mileage. It takes about a half tank of gas to drive 30 miles. I live in the San Francisco bay area. I generally drive like a grandmother; I never "floor it."

We already checked the fuel injection pressure regulator, and that is fine. There don't seem to be any vacuum leaks.
We cleaned the air filter and vacuumed out the case the air filter sits in.
We cleaned out the throttle body with Chemtool.
I ordered a Denso upstream oxygen sensor for $32 and plan to put that in when it arrives.

When the car is first running, we do smell gasoline, although it's not visually leaking from anywhere. I'm wondering about the possibility that the fuel injection system could be leaking gas internally?? Any opinions? Thanks.

 

[trlhiker]

Half a tank in 30 miles. You definitely have a leak. Are you checking for leaks when the vehicle is running? Have someone press the accelerator while you look for leaks?

 

[Scott O'Kashan]

Don't replace the oxygen sensor sensor unless it has been diagnosed as being worn out. There is no need to replace parts that don't need replacing and this is a tremendous waste of money to do so.

If you smell fuel, there has to be a leak somewhere. Find it. Get the car on a lift and look underneath the car, following the fuel line from the gas tank all the way to the engine. Again, if you're smelling fuel, it's leaking somewhere. It is impossible for a vehicle to be consuming 6+ gallons of fuel in only 30 miles. That would be 5 miles to the gallon and that's the fuel economy an 18-wheeler truck gets!

 

[Lois]

We looked all around the engine compartment and under the car while it was running and couldn't detect any gasoline leaks. That's why I asked if anyone knew about the possibility of these cars somehow leaking within the fuel injection system where we cannot see it.

I will try pressing on the accelerator while my partner looks for leaks, however. We haven't tried that yet.

With this poor gas mileage and the cost of gasoline, fortunately I don't drive very much.

 

[Scott O'Kashan]

The only way to correctly diagnose this fuel leak is by getting the car on a lift at an auto center. Fuel doesn't have to be dripping on the ground for a leak to be present. If you are actually smelling gas, it can only be because of a leak, which is also very dangerous and can cause the car to catch on fire.

Get it to a competent professional as soon as possible, before disaster strikes.

 

[corolla_mike]

If you smell gas, and cannot find a leak, my best guess is that you need a carburetor overhaul -- and a complete one, not just a "rebuild". If your Corolla is burning a half tank of gas in 30 miles, that is a tremendous amount of fuel getting into your engine, and you run the great risk of "washing out" your cylinders. If that happens, your engine will be ruined.

If it was my car, I wouldn't drive it until I had the carburetor rebuilt or replaced.

 

[Lois]

Hello,

I found a good mechanic who computer-diagnosed my car for $65. The problem was that it was running rich and needed a MAP sensor and oxygen sensor. The engine is fine.

Lois

 

[401DROP]

try your egr valve its a pain to replace but i just had to do it. A few weeks ago i was having bad gas milage i cleaned my throttle body worked better bus was not all there. Now i replaced the egr valve and its like new agin..( 96 corolla 1.8)

 

[Lois]

Finally got the mpg problem diagnosed correctly!

Well here I am much later, and I finally got my problem fixed.

The oxygen sensor and map sensor that a mechanic recommended in January 2012 hadn't improved my gas mileage. Yes, my car was down to about 8 miles per gallon last week. Talk about frustrating! Thank goodness I don't need to drive it much.

So it did not pass smog recently and I took it to a new mechanic last week. He had it for a couple of days, checking a number of things, and he came up with a problem with the air temperature sensor. He replaced it (an inexpensive part) and now my car is getting 30 miles per gallon. After all this time of getting horrible gas mileage, it's finally running like it is supposed to.

In addition to the air temperature sensor, the mechanic is now replacing the egr valve and cleaning the intake manifold. So I may even get better than 30 mpg. The mechanic is doing this work because my car did not pass a smog inspection last month. (I'm in California.)

 

[Scott O'Kashan]

If the recommended oxygen and MAP sensor didn't rectify the problem you brought the car in for, you don't have to pay for it. That's the law. Anything less is stealing/incompetence on the part of the mechanic and you don't have to pay for that. Demand a refund. If they give you grief, contact your state Office of Consumer Affairs and also the Attorney General's Office.

 

[Lois]

reply to Scott

Well the oxygen sensor and map sensor were reading out-of-range, so they probably were defective. Replacing those parts just didn't improve my mpg because of the faulty air temperature sensor.

The current mechanic spent two days on my car, checking and diagnosing it. That's how he found the bad air temp sensor.