'84 Corolla guzzling gas??

[Thonor]

Hi All:

I'm looking for some help brainstorming my problem. I have an old '84 Corolla 4AC, RWD standard tranny that is absolutley sucking gas. The gas milage is about half of what it was a few years ago. It used to be around 35mpg, now it is less than 20mpg.

The car runs great and idles great with no problems at all - it just has terrible mileage.

Things I have done:
- Replaced spark plugs
- Adjusted engine timing
- Replaced air filter
- Cleaned out the carburetor

Things I have NOT done (let me know what you think):
- Replace O2 sensor
- Cylinder compression tests
- Vacuum test

Anything else I should try to get the mileage back where it used to be?

[CJCride]

Originally Posted by Thonor

Hi All:

I'm looking for some help brainstorming my problem. I have an old '84 Corolla 4AC, RWD standard tranny that is absolutley sucking gas. The gas milage is about half of what it was a few years ago. It used to be around 35mpg, now it is less than 20mpg.

The car runs great and idles great with no problems at all - it just has terrible mileage.

Things I have done:
- Replaced spark plugs
- Adjusted engine timing
- Replaced air filter
- Cleaned out the carburetor

Things I have NOT done (let me know what you think):
- Replace O2 sensor
- Cylinder compression tests
- Vacuum test

Anything else I should try to get the mileage back where it used to be?

I don't think the 84 has a O2 Sensor not sure though. You did not goof up the timing? Choke plate opens fully when warmed up{no binding}? Fuel filter is a pretty easy replace{COLD ENGINE}.

[Brian]

Yeah, no 02 sensors on those things if I remember right. Definately check for a stuck choke. Clean the OUTSIDE of the carburetor & linkages with some choke & linkage cleaner (carburetor cleaner). Move those linkages and widgets around and make sure everything moves smoothly. If you're still having excessive fuel consumption issues, you may need to take the top off of the carburetor and clean out the bowls, etc.

[Thonor]

Thank you guys - I will try cleaning out the carburetor.

I've done engine timing many times before and it should be at 5* BTDC @ 1000rpm. Right now, it is at exactly that.

The other thing I just noticed last night is the "fake EGR" pipe that leads from the exhaust manifold into the air intake is missing. I'm not sure of what that is supposed to accomplish, but I'll replace that right away.

I also put half a can of Seafoam in the gas tank to clean out the inside of the engine, but when I changed the plugs they were clean, so I don't expect that to do much.

Any other ideas?

[84Hachi]

Originally Posted by Thonor

Thank you guys - I will try cleaning out the carburetor.

I've done engine timing many times before and it should be at 5* BTDC @ 1000rpm. Right now, it is at exactly that.

The other thing I just noticed last night is the "fake EGR" pipe that leads from the exhaust manifold into the air intake is missing. I'm not sure of what that is supposed to accomplish, but I'll replace that right away.

I also put half a can of Seafoam in the gas tank to clean out the inside of the engine, but when I changed the plugs they were clean, so I don't expect that to do much.

Any other ideas?

I preformed the whole seafoam bit in my SR5, the car is better in mpg, putting seafoam in the gas tank is one of three things you can do with that can, the others in the oil and a vacuum line, I did all three and i must say the best 8 bucks i ever spent. before you had to keep cranking it to start now you barely have to touch the key to start it, it idles so much better.

[verlaryder]

You never said anything about the exhaust. If the exhaust is stinky then the most likely cause is ruptured auxillary accelerator pump diaphragm - a part on the lower left hand firewall facing side of the carburetor that's secured by three screws. There's a vacuum hose attached to the AAP - pull it off - if there's liquid gasoline inside it then you know the AAP is bad. The AAP is a $30 part you can order from a Toyota dealer and you would need to remove the carburetor to access it. A temporary fix is to pinch the hose somehow to block the flow of gasoline -maybe use a sturdy hair pin or nylon tie

[Thonor]

Here's a quick update:

After cleaning and replacing just about everything that can be easily cleaned or replaced I found a cracked HIC (high idle compensation) hose. I've replaced that hose and also replaced the preheater pipe.

The carburetor actually appeared to be working really well - I've cleaned it out several times over the years. I checked the idle, fast idle and throttle position and those were all right on spec.

The gas mileage is back up to about 28mpg, which is a welcome improvement from the 17mpg I got before all the tune-ups.

I think the cracked HIC hose was responsible for the majority of my problems. I didn't check the aux. accelerator pump - but I will do that shortly.

Thanks one and all for the help.