Gas Leak Can it be a bad computer - 1990 Lexus LS 400

Any very small leak between tank and pump can suck air instead of fuel, even if it doesn't leak gas. Also, just because a pump is new does not mean it is good. I ahve had many new bad parts over the years. Bad gas cap that should be vented can also cause issues.

First off it is hard to diagnose cars without seeing them. That being said the most common cause of these 2 problems occurring together and being worse when the engine is cold would be a vacuum leak. Because a vacuum leak is a mechanical problem it is not computer controlled and therefore will not show up as a code until the problem is so bad that computer assisted components can no longer control it. The scanner will show higher short term fuel trim data because the computer will be adding extra fuel. ( Hence the bad gas mileage). The easiest way to find this leak is to purchase a can of carburetor cleaner. Use the plastic straw on the can and spray carefully around the intake manifold. When an air leak is found by the carb cleaner the engine rpm will rise. As you get closer to the leak spray less and less cleaner and be more aware of wear you are spraying.

you have something allowing the gas fumes to leak out of your emission system is what code po422 means if you replaced your gas cap and this code came back after resetting your check engine light then some where in the vent line between the fuel tank and the intake there is a leak that is allowing the gas tank to depressurize which will turn on the light and cause your cars ecm or computer to go into (limp mode) this is a preset program which allows the driveline to operate at a non optimum setting or diagnostic setting meaning it will get lousy gas mileage until repairs are made and the problem is fixed as far as being safe to drive it could be very dangerous depending on how bad the leak is and weather the car has exhaust leaks also you are dealing with gas fumes closed in say like parking in a garage where these fumes can build up it can be very dangerous if enough fumes build up in such a instance out in the open not very bad at all

is it possible to give code? because that fuel leak code is common in diesel, it may mean bad injectors or bad fuel pump. the common rail is not able to reach target pressure with ease so that computer detects a fuel leak.

Sounds like a bad tank or line... Does it leak when the car is not running? If it only leaks when you running you have a bad line. If you leak all of the time then the tank needs replaced.

Getting a smoke test is the right direction to go in.
The computer vents the gas tank to the vapor canister while the engine is running. It also pressure tests the system for leaks. Some where between the gas tank and the vapor canister there may be a leaking hose or valve. Or it could be the gasket on top of the tank where the pump assembly went in.
The gas cap could have been a source for the leak, the other things are not involved.

Check this info about P0455 - Evaporative Emission Control System Leak Detected (no purge flow or large leak)

This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.

Causes: A code p0455 most likely means one or more of the following has happened:
A loose or improperly affixed gas cap
A non-conforming gas cap (i.e. not factory/original brand)
Other leak or damaged piece in EVAP system

Possible Solutions: With a p0455, the most common repair is to:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary


Check it and keep us updated.

not much to go off here, but i would think if you are always smelling the gas after you shut it off and it is not someone around you, then yes, you have a leak. This leak could be the gas cap even. Sometimes o-rings on the fuel rail can go bad causing it to drain off the excess gas when shut off. but you would notice really bad gas milage. I hope this helps as your description was pretty vague.

evap is a valve which draws gases from the petrol tank, through a charcoal canister, ususal problem is air leakes from pipework and i have a had a few evap valves go down. the valve is in the engine bay two wires two pipes.
Good luck Davelee

p0441 - Evaporative emission control system Incorrect purge flow. can be caused by a lot of things and is usually related to a small leak in the emission control evap system, try replacing the gas cap and see if it helps, if not, the system needs to be tested for a leak with the scantool or a leak tester or both.
usually you will see p0440 p0441 and p0446 together but before anything replace your gas cap and besure to tighten it down when you gas up the vehicle, 90% of the time with those codes either a loose gas cap of bad gas cap gasket is the problem

Otherwise - Might be a canister leak, defective VSV valve or hoses, bad gascap seal.

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