Toyota loses tons of gas mileage please help!

1986 toyota corolla gts (ae-86) my friend owns and says that over a course of three days he lost half a tank of gas from driving to school and back which in total is only about 15 miles or less. we have checked for leaks and the spark plugs and the wires are good. we are about to check the O2 sensor to see if its failed.

we any and all suggestions.

He “lost” half a tank of gas?
Or does he think that he actually used/burned that much gas?

You tell us that there are no apparent leaks, so the implication is that the car actually used 1/2 of a tank of gas to drive 15 miles. This leads to two possible conclusions:

  1. The car is in very bad shape mechanically.
  2. The gas gauge is not accurate.

On what is he basing this estimate of gas usage?
If he is basing it on gas gauge readings, please remind him that a car gas gauge is not a laboratory-grade measuring device.

He needs to calculate the amount of gas used by filling the tank and dividing the number of miles driven since the previous fill-up by the number of gallons needed to refill the tank. If he does this, and averages his calculations for three fill-ups, I can virtually guarantee that his car is not using 1/2 of a tank of gas to go 15 miles.

Check for a thermostat that’s stuck open, a choke that’s stuck closed, or for a faulty Thermostatic Vacuum Switching Valve located on the thermostat housing.


Is there a possibility that the gas was siphoned out of the tank? Otherwise checked the mpg as suggested by VDCdriver.

Ed B.

thanks ill tell him

will do. did you own one of these Tester?

dont think so. its very hard to get the gas tank open trust me its taken me 5 minutes to get it open with the normal lever before

No. Never owened one. But repaired a lot of 'em.


that must have been fun.

Someone stole his gas or his gauge is wrong!

Knowing the car and its audience I have a bias. So I say someone took the car out for a joy ride.

No chance the gas is in the crankcase? Let all the other readers know your 02 sensor checking method.

we checked the O2 sensor by the book by shorting 2 of the terminals in its service connector and then connecting a volt meter to 2 terminals and kept the engine at 2500 rpm and it was suppose to deflect more than 8 times in a 10 second period and it deflected 13 times so its good

One other thing.

Pull the dipstick out and smell the oil. If it smells like gas, the diaphram in the fuel pump might be leaking.


the fuel pump is in the gas tank and the car is fuel injected not carburated so how is it possible for the 2 to mix

An injector that is constantly being told to fire is one way, I have seen a pinched wire harness do this (caught under the valve cover after a valve adjustment)

would cracked or broken fuel injector connectors cause them to short and continue firing?

No, I can’t picture how, the failure would have to be in the harness or fuel injector its self, Hey have you checked fuel pressure? perhaps it is way high

no we havent guess well look at that tomorrow.

Your friend must have the 4AGE engine, if its an AE86, then its rear wheel drive. This is a vary popular vehicle with the drift crowd and gets a high price on the retail market.

I think, but not 100% sure, that this engine has a cold start injector. It could be leaking. When it leaks, it leaks into the intake manifold. The excess fuel washes down past the rings into the oil pan. This is why several people have asked you to check the oil for the smell of gas.