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1997 4.0 cel

Alecs

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1997
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Ford
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Hello all. I'm new here and I'm having some issues with my pickup. It's a 97 with the ohv 4.0, 5 speed, rwd.
Just recently had my ECU replaced and I'm now throwing codes p1443 and p0420.
I was wondering if any of you had any insight on the matter out advice. Thanks in advance.

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Alecs

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I know what the codes are,I just need to know probable causes and fixes for them.

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RonD

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EVAP system code is most likely a cracked vacuum hose or solenoid issue

EVAP system sucks air out of the fuel tank when engine is running, this is why you hear a sucking sound when you open the gas cap when fueling, tank has negative pressure inside, if you don't remember hearing this sound recently then EVAP system is not working.

There is a charcoal canister in the engine bay, there is a vacuum hose from the intake manifold that runs to a solenoid near this canister and a hose from solenoid to canister, computer opens solenoid to apply engine vacuum to canister.
And there is a long hose from canister to fuel tank.
There is a pressure sensor on one of the hoses that tells computer there is negative pressure in the tank, sensor moves around year to year so check out where it is on your year.
Check your gas cap, if it isn't sealing the tank then negative pressure can't build up and you get a code.
Also the filler hose and vent hose on the tank can crack, this is the same as bad gas cap because pressure can't build up.
The solenoid is just a 12volt open, no volt closed device, so you can test it with the battery, you will hear it click open when 12v and ground is applied to it, there is no +/-, so polarity doesn't matter, as long as it is disconnected from engine wiring.
If you need to change solenoid you need to heat up the hoses to remove them, gently heat them, lol.

EVAP codes are notorious for hanging around, even after you fix the problem the code will stay, you need to keep the fuel level in the gas tank between 1/4 and 3/4, so don't run to Empty and don't fill up, drive it a few weeks and code should go away on it's own.
Computer runs EVAP tests in it's own sweet time, no way to force an EVAP test, and EVAP system must pass the test several times before computer will clear the code.


On a OBD II vehicle(1995 and newer) there is an O2 sensor located after the Catalytic converter(downstream, bank 1, sensor 2), the Oxygen reading on this sensor is compared to the Oxygen reading on the "upstream" O2 sensor(s), if the Cat converter is not "cleaning up" the exhaust like it should then you get that code.
So Cat converter could be bad or O2 sensor could be bad.
Check connections on this rear O2 sensor, they often get water inside the connector, also the wires can get damaged.
 
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