Passing without CATs

[stevenf]

My dads 96 F-150 straight 6cyl has been acting up lately and running rough. His engine light came on and it ran the cat converters. The man that read him the codes said the converter was going out.
I know there are 2 sensors before the cat and 2 sensors after. The ones after are the ones reading the cat is out?
How do you know if its not just a bad sensor? Also, I have known of several people running with no cats and never had emission problems. What do they do to there ECU to make it read no error?

 

[Ranger5.0]

ok, one. You cant run without a cat, is ilegal and just dumb. There are two sensors, one upstream of the cat and one down stream. Its not the ecu that makes it fail the smog test, is the exaustgasses that make alow it to pass or make it fail or pass.

 

[Jimmeh]

My dads 96 F-150 straight 6cyl has been acting up lately and running rough. His engine light came on and it ran the cat converters. The man that read him the codes said the converter was going out.
I know there are 2 sensors before the cat and 2 sensors after. The ones after are the ones reading the cat is out?
How do you know if its not just a bad sensor? Also, I have known of several people running with no cats and never had emission problems. What do they do to there ECU to make it read no error?

I'm also curious about the last question you asked, mainly because I don't want to see the CEL all the time.

As far as the cat being out, it's possible, but I don't think it throws a code. You could gut the cat, or you could try changing the O2's.

 

[stevenf]

The only way to find out if the cat or sensor is bad is to replace the cat or the senser after the cat?
Someone has got to know more. I have seen so many ricers and decked out cars running with no cats. They get something done to the computer, but I dont know what.

 

[stevenf]

he said that the code was that the cat was bad due to a misfire in the ******.(He doesnt remember). So he replaced the spark plugs, wires, distributor cap because he thought it was a misfire in the engine. That didnt fix the problem.

 

[stevenf]

Are there anyways to know which o2 sensor is bad?

 

[97ranger4x4]

Short of purchasing 1. Then replace one of the bad 02 sensors. if the problem goes away, then your done. if it still exists, try the other 02 sensor. Unfortunately if both are good, then you just wasted $$$ on a o2 sensor.

 

[Wicked_Sludge]

holy. cow. settle down.

first, if the code that was retrieved was a cat efficiency code, then you have no reason to believe there is a fault with the UPSTREAM sensor (that is, the sensor on the engine side of the converter).

second, you can trick the DOWNSTREAM sensor into thinking the converter is working properly, even if its missing or malfunctioned, but the truck will still fail the sniffer test. you will not pass emissions without a cat converter whether your CEL is on or not. and even if you could, its is against federal law to tamper with original emissions equipment...read that like this: "big f@#ing fine".

a misfire will kill a cat converter because it causes raw fuel to be dumped into the exhaust, thus overheating and melting the substrate. whatever is causing the misfire needs to be fixed or else the new cat will not live long.

open the exhaust up and shine a light into the converter. if you see blobs of melted substrate in the bottom, it needs replacing.

 

[turbo cat]

a mil eliminator or a handheld proggrmamer can turn of the cel. as for passing 96s are eec v (OBDII) they run the test from the diagnostic port. mil eliminators or a tune will help the ecu pass the test. If the motor is runing well and in tune and is mostly stock chances are you will still pass a tail pipe test. I passed tests plentry of times without it once on a chevy 2.8l s10 and on a ford 302. If the motor has an timing issue or fuel problem, vaccum leak, rough idle, worn sensors like o2 you will fail. funny enough the best results ive ever seen on a readout after a test the old 2.8 tbi with only a muffler

 

[stevenf]

Ok, If you got the codes about the cat failure because of a misfre in *****. You changed the plugs, wires, cap and rotor but still have the problem. What would you try next?

 

[Ranger5.0]

try finding the cause of the misfire, not throwing parts at it. it will save frusteration.

 

[stevenf]

Thats my question, How would you go about doing that? The computer isnt giving off a specific cylinder where the the misfire is happening.

 

[Wicked_Sludge]

could be a million different things...you need to start systematicly ruling things out. hooking a vacuum guage up can tell you a lot about the health of a motor (this would identify sticky valves/lifters). a power balance test, injector flow test, check for vacuum leaks base timing check, filters, the list goes on.

 

[stevenf]

Why would it mention the Cat converterfailure due to misfire? Does that tie in to something to point me in the right direction? Or is the o2 sensor saying the cat is failing because of the engine misfire? Or is the cat bad and causing the sensor to make the truck misfire?

 

[Wicked_Sludge]

it probably didnt. it probably had a cat efficiency code AND an engine misfire code. it would really help to know what code exactly.