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Adverse Affects of Gutting Cats

fastpakr

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Its probably running in open loop permanently due to the sensor delete.

No cats is for carbs. EFI doesn't like it.
EFI really doesn't care that much. It will trigger an alert that the converter isn't running at full efficiency, but that's separate from the upstream sensor's data used for input data to the computer.

Again - I'm 100% not advocating for doing this. Just clarifying that it won't cause running issues.
 


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EFI really doesn't care that much. It will trigger an alert that the converter isn't running at full efficiency, but that's separate from the upstream sensor's data used for input data to the computer.

Again - I'm 100% not advocating for doing this. Just clarifying that it won't cause running issues.
Yep, I don't think it would enjoy having to do that though.
Its like picking your nose with a different finger.... easily possible, but not ideal.
 

fastpakr

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Not sure what you're getting at. It literally just triggers an error code leading to a CEL. The computer doesn't care one iota beyond that. The downstream sensor data has no value other than monitoring if the converter is working adequately.
 

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A honeycomb-type catalyst in good condition should flow freely without significant exhaust restriction. The only OEM catalysts (that I know of) that were known to restrict exhaust flow were the old GM designs with the replaceable pellets. Those did stop up the exhaust unnecessarily, and GM went to the honeycomb design after a few years.

Note that oil fouling from burning oil, excessive temperatures, and physical damage inside can all affect catalyst performance. But that has nothing to do with any faults in most catalyst designs.

In Virginia most of the state does not normally have emissions testing, but during state safety inspection the inspector is supposed to eyeball the emissions system to make sure everything is there. So it's not just California.

I like clean air myself and would not gut a cat. That kind of stuff gives certain do-gooders cause to target the car hobby and those who like do-it-yourself repair and maintenance.
 

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Parts of texas are visual also. My county is
 

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Pa got rid of the sniffer, but check for any CEL and visual. Any CEL is considered an automatic fail for your emissions sticker.
 

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How do they check the check engine light? That bulb burned out a long time ago, and I never had a bit of luck finding an OBDII reader, or really figure out how to read one with a paper clip. I think I did put something in there above the Cat once
 

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How do they check the check engine light? That bulb burned out a long time ago, and I never had a bit of luck finding an OBDII reader, or really figure out how to read one with a paper clip. I think I did put something in there above the Cat once
When you first turn the key to start a vehicle, the computer turns on all the dash lights so that you can find the burnt out ones. The mechanics look for that. That said, on my 86 ranger, there is no cel light from the factory. And maybe for 87 too, but not sure.
 

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25 year plus vehicles are exempt from emissions except the gas cap. Has to have a gas cap.

If the CEL doesn’t turn on with key on, that’s a fail. Otherwise they plug into the OBDII to look for an all clear. They plug into a computer that reports back to the state. If they can’t do that, for whatever reason, automatic fail.

If they don’t see an EGR = fail, no cat = fail.

The inspection stations are licensed by the state, but not state run. So mostly they are want to not lose their inspection license by. The state does make it hard for them.
 

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NH has OBD II emissions testing because we were threatened with the loss of our federal highway money if we didn't. It applies to 96 and newer vehicles under 8600 gvw. Verifying the MIL function is the first thing the Gordon Darby unit asks for, then it does a scan and any monitors that are incomplete will fail the test. Some foreign cars can have incomplete monitors and still pass for some reason, real cars need to actually pass. I had about a 20-25 minute road test route that I would use to clear customers monitors after repairs so we could inspect the vehicle.
Cats from the 70's were restrictive, modern cats flow much better so gutting one out won't do anything other than make the V6 exhaust note sound obnoxious. Think of your cat as a stainless steel resonator that will never rust out.
 

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One of the adverse effects is getting your post deleted… bottom line is that it’s illegal on ALL street driven vehicles in the US, even if you don’t have emissions testing in your area.
I'm in NO WAY promoting this! I just wanted to know what adverse effects, if any, it would have on the engines performance and if what I was saying was correct. I guess I was wrong. I've heard in the past that it can cause problems with backpressure (which is necessary on some engines, I believe) and other issues such as A/F ratio. However, what I heard must be wrong. That's why I asked the question; to better understand. If I didn't ask, I would still think that what I've heard was true. But now I have the correct information! If I ever have to replace the cats I will either go to the bone yard or get some decent high flow after market cats. Especially since it's not good for the environment which is already screwed up! I hate being wrong but this time I am. When I had the custom exhaust done on my mustang, I watched the guy use a crayon to draw a line down each side all the way to the muffler. He ran the engine until the line melted away in a certain spot and that's where he put the cross-over pipe. He explained how the pulses in the exhaust system work and that where the line melted is where back pulse (revision) from the muffler met the pulse coming from the engine. That's where the pipe got hot first and by putting the cross pipe there it "balanced" the exhaust. He is the one who told me that what people who gut the cats don't realize is that they are causing the exhaust to become unbalanced which causes performance issues. I'm not an exhaust specialist so for all I know he could have been feeding me a bunch of BS! My mustang was carbureted so maybe that made a difference.
 

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Not sure what you're getting at. It literally just triggers an error code leading to a CEL. The computer doesn't care one iota beyond that. The downstream sensor data has no value other than monitoring if the converter is working adequately.
He said he used an adapter that lifts the O2 sensor out of the exhaust stream and tricks the PCM into thinking everything is working. He isn't getting any CEL so it must work. I Googled it and found out what he was talking about. It's just an extension that screws into the bung and then the sensor screws into that, thus lifting the sensor up out of the exhaust stream. I'm not sure how they are even legal to sell! Their sole purpose it to prevent the CEL from coming on. Here in MA they don't check for things like that but I imagine in other states where the actually look for the cats they would see it and fail them.
 

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I'm in NO WAY promoting this! I just wanted to know what adverse effects, if any, it would have on the engines performance and if what I was saying was correct. I guess I was wrong. I've heard in the past that it can cause problems with backpressure (which is necessary on some engines, I believe) and other issues such as A/F ratio. However, what I heard must be wrong. That's why I asked the question; to better understand. If I didn't ask, I would still think that what I've heard was true. But now I have the correct information! If I ever have to replace the cats I will either go to the bone yard or get some decent high flow after market cats. Especially since it's not good for the environment which is already screwed up! I hate being wrong but this time I am. When I had the custom exhaust done on my mustang, I watched the guy use a crayon to draw a line down each side all the way to the muffler. He ran the engine until the line melted away in a certain spot and that's where he put the cross-over pipe. He explained how the pulses in the exhaust system work and that where the line melted is where back pulse (revision) from the muffler met the pulse coming from the engine. That's where the pipe got hot first and by putting the cross pipe there it "balanced" the exhaust. He is the one who told me that what people who gut the cats don't realize is that they are causing the exhaust to become unbalanced which causes performance issues. I'm not an exhaust specialist so for all I know he could have been feeding me a bunch of BS! My mustang was carbureted so maybe that made a difference.
2 things:

1. I was making sure everyone knows that this topic is frowned upon here.

2. It’s reversion, not revision.
 

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When you first turn the key to start a vehicle, the computer turns on all the dash lights so that you can find the burnt out ones. The mechanics look for that. That said, on my 86 ranger, there is no cel light from the factory. And maybe for 87 too, but not sure.
'88 was the first year.
 

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it can cause problems with backpressure (which is necessary on some engines, I believe)
No engines require exhaust back pressure, this is a myth.
Someone else above mentioned exhaust savaging. witch is all related.
You want to get your exhausts velocity as high as possible, if you make the pipes too big for the amount of exhaust that needs to flow then you are going to start to decrease the exhausts velocity. This is where that myth comes from, you put too big of an exhaust on and you loose your bottom end because you are not flowing enough air to have effective exhaust scavenging.

An exhaust system is only going to have peak effectiveness at a certain RPM range on a given engine.

Then someone says "this engine must need some back pressure to run right."
 

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