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No cat and running extreamly rich

This is a discussion on No cat and running extreamly rich within the LT1 forums, part of the Vehicle Specific category; I removed the cat off my '94 Z-28 M6. Before i removed it the car ran fine now that i ...

  1. #1
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    No cat and running extreamly rich

    I removed the cat off my '94 Z-28 M6. Before i removed it the car ran fine now that i have removed it the car is running extreamly rich and sets off the check engine light. When the light is off it loads up really bad and boggs down anywhere from 3g-4g untill i burp the throddle. I also bags out/pops really bad but when and my fuel mileage plumits. When the light comes on the car seems to run good but i know its still really rich. It has sum smoke coming out when im sitting still and very gassy smelling exhaust. I thought about putting some O2 simulators on there then found out that they only work on 96 and new vehicles. What are some things i can do??????

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    Impounded MikeSomething's Avatar
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    Get some stuff called "Sea Foam" from an AutoZone or somewhere like it. I don't know much about the '94's but your probably gonna need to tune it out w/ something (software, programmer etc.). You can always just buy a highflow cat if it gets really bad for ya.

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    Member Chad97z's Avatar
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    What codes are in the ECM? Do you have O2's on it now? If not, I would reinstall them or at least check them if you can for proper operation. You might be able to pull them out and test the resistance between the leads. A device like an O2 sensor will have X amount of resistance when its cold. And there is a range it should be in for it to me working properly.

    Make sure your MAF is connected and all your sensors including the air temp in the intake. Simms won't really fix your problem. Simms are used when people put headers on their cars and no O2 sensor mount is on the headers OR they have a custom program and trick out the ECM. I would not try to trick the ecm just yet if your trying to get more HP. First thing first. Get it runnign right, then screw with the simms later. You need properly functioning O2 sensors on it. And the SES code.

    And the absence of cats should not make it run rich.. Cats dont remove fuel from the exhaust.. Cats remove carbon emissions.

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    Pathelogical Liar BlackLT1Z28's Avatar
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    Yeah, go to autozone and get the codes.
    But there are no O2 sims for the 93-35 LT1's because there are no O2 sensors after the cat(s), just one for each bank of cylinders before the y-pipe.

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    Member Chad97z's Avatar
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    Getting the codes are the first step, but as a side note, O2's are very necessary unless you have a custom program. I suggested leaving the O2's on the car. Your car will run better and have better fuel economy and its not as suseptible to climate change. If you want to replace the O2's, then you will have to do it with a tool like I have below.

    When my O2 went bad, I got a code in the ECM. To replace them, put some rust remover on the O2-header joint and let it set a while. Then disconnect the O2 from the harness.. Then put the socket and extension on the O2. Then start with your engine and apply pressure to the O2 and begin trying to turn it.. As the engine warms, the header will expand and the grip between the O2 and header will be not as tight. So as the engine warms the exhaust, you will feel the O2 break free from the header. When it loosens, turn off the engine. And continue to unscrew the O2.

    I only replaced the passenger side O2, so I have never done the drivers side.. Cant tell you much about the drivers side.

    The SES light will come on when you turn on the engine with the O2 disconnected from the harness.. but it aint nothing but a thang. Just when your done, remove the power from the battery and it will clear the codes in the ECM..


    BlackLT1Z28 don't slam me too hard for not having headers... (YET)




    hella extension
    Last edited by Chad97z; 01-25-2008 at 10:30 PM.

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    Senior Member Z06-Goose's Avatar
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    Quote Originally Posted by LT1Redneck View Post
    I removed the cat off my '94 Z-28 M6. Before i removed it the car ran fine now that i have removed it the car is running extreamly rich and sets off the check engine light. When the light is off it loads up really bad and boggs down anywhere from 3g-4g untill i burp the throddle. I also bags out/pops really bad but when and my fuel mileage plumits. When the light comes on the car seems to run good but i know its still really rich. It has sum smoke coming out when im sitting still and very gassy smelling exhaust. I thought about putting some O2 simulators on there then found out that they only work on 96 and new vehicles. What are some things i can do??????
    You don't need to find out what codes your car is throwing. Everything happening right now is related to you having removed the cat. That simple.
    I wasn't aware that the O2 simms are for the 96 and newer, but you can probably program out the issue. By not having a cat, the O2 sensor readings is off the chart. The O2 sensor is seeing more air than normal, and it's telling your PCM to dump more fuel. Eventually your plugs are going to foul up and the car will run even worse. The "gassy smell" it's also very obvious; no cats.

    Perhaps somebody else can chime in on the O2 simm question. I would think there have to be some out there by now
    Goose-
    2007 Audi RS 4

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    Member Chad97z's Avatar
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    If he doesn't have an O2 sensor after the cat, then how can the ECM see more air when the cat was removed?

    Like I said, get the code. And make sure the O2 sensor is connected. Someone might have disconnected the sensor while dropping the exhaust to remove the cats. hehe


    The reason they put a O2 sensor after the cat (if he had one) is because there has to be enough oxygen in the exhaust to allow the catalyst to burn the unburned hydrocarbons and CO. So if there is too much oxygen in the exhaust after the cats, then it's too lean. If there is not enough air in the exhaust after the cats, then there might be unburned emissions in the exhaust. So the O2's don't monitor fuel.. However, if too much air is in the exhaust after the cats (lean) Or if too little air is in the exhaust (bad for emissions burning) then the ECM will adjust the fuel mixture accordingly to achieve the desired oxygen level in the exhaust. There is no monitoring of the emissions of the exhaust of any car. No system actually reads the real time emissions of the car. All it can do is guess at the emissions level by reading the amount of air in the exhaust. You need to have your car inspected to see how many pollutants it has.

    The entire focus of having a catalytic converter and a system the detects the amount of oxygen in the exhaust is driven by the need for a cleaner running vehicle.. Not for the sole purpose of Fuel to air mixture for max performance. If that was true, then the stoichiometric point of 14.7:1 would not be used.

    And the reason they put a O2 sensor before an after the cats on newer cars is to detect if a cat is not doing its job of burning emissions. They do that by again monitoring the air in the exhaust. If the same amount of air is in the exhaust before and after the catalyst, then the catalyst is not burning off emissions. That is how they detect a bad cat.

    http://auto.howstuffworks.com/catalytic-converter2.htm
    Last edited by Chad97z; 12-24-2006 at 05:57 AM.

  8. #8
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    I appretiate ya'lls help. I will have 2 stop and pull the codes next time im by the parts store.
    '94 Z-28 M6 K&N CAI, ORY, Unscreen MAF, TB Bypass, TB Air Foil, Flowmaster 80 series, Centerforce Clutch, 160 degree therm., 18X10.5 rear and 17X9.5 front Z06R wheels. soon to be taken to the track

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    Member Chad97z's Avatar
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    do you think your O2 might be disconnected or not fully seated on the O2? After all this, I'm sorta curious to find out what the problem is.. haha

    On the 94 model, can't you just use a jumper wire to ground the test lead on the ALDL? If you have a haynes book, see page 6-2 and 6-3. It is the emissions section. You should not need a scanner to read the codes. So no need to buy a scan tool or pay a shop to read the codes.

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    Pathelogical Liar BlackLT1Z28's Avatar
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    Quote Originally Posted by Chad97z View Post
    do you think your O2 might be disconnected or not fully seated on the O2? After all this, I'm sorta curious to find out what the problem is.. haha

    On the 94 model, can't you just use a jumper wire to ground the test lead on the ALDL? If you have a haynes book, see page 6-2 and 6-3. It is the emissions section. You should not need a scanner to read the codes. So no need to buy a scan tool or pay a shop to read the codes.
    Autozone will read codes for free, so he won't have to go through the trouble of all that.

    It could be an O2 sensor-related problem. He could have damaged it upon removal/reinstalling it and now it doesn't read properly. But, like I said before, there are no sensors after the cat(s), just 2 before. After I installed my headers, I only had one good O2 sensor, because my passenger-side one was stuck in the manifold. (yeah, yeah, yeah, I tried almost everything, but I couldn't heat it up because I didn't have a torch. And by the time I had access to one, the head on the O2 was disformed so badly, it would have been impossible to reinstall it) So, I just bought one off of e-bay. But before it came, I drove around with 1 O2 sensor and open headers. It didn't even throw an SES light...hahahaha, it was just reading off of the left side.

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    Member Chad97z's Avatar
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    It probably doesnt matter now, but you dont need a torch to remove the O2. Just start the engine like I mentioned above.

    By the way, how loud is it with open headers? I am going to install my headers myself if I keep this car and then I will drive it over to a muffler shop for the welding of the rest of the exhaust. So it will be loud on the drive over to the shop. I wonder if I would get pulled over by a copper.

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    Pathelogical Liar BlackLT1Z28's Avatar
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    Open headers are louder then SHIT! Any video on the net will not do them justice. You will get a headache driving around with them a lot. But if you get pulled over, just tell the cop that you just put them in and you're driving the muffler shop to get the rest of the parts installed. They should just give you a warning.
    But DO NOT get your exhaust welded on. Bad idea! Just use clamps. If you weld everything on, you can't disconnect the headers from the heads if you are going to get head work or new heads installed. The y-pipe will interfere with tranny work, so you'd have to cut the welds will future work under the car. Again, welding the exhaust is a BAD IDEA. My fucking muffler shop welded certain parts of my exhaust together and it PISSED ME OFF. I'm still mad about it. So, just clamp everything. You'll be happier in the long run.

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    Member Chad97z's Avatar
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    well cool.. Maybe I should just buy all the parts that snap together. haha That would save me money. I hate paying someone for service. (no pun). haha What about mufflers? Have you ever installed a whole cat back including the muffler?

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    Pathelogical Liar BlackLT1Z28's Avatar
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    Not yet, but I will this spring when I replace the flowmaster catback that came on the car for loudmouth. Should be cake though. My friend is going to let me borrow a sawz-all.

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    Member Chad97z's Avatar
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    I hear a lot of people gettn rid of their loud mouth.. Its just too much..

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    Pathelogical Liar BlackLT1Z28's Avatar
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    I had just the catback on my last Z and it was good. But I can't wait for it with my LT's. I'm not worried about the noise/sound. Its going to sound mean a hell.

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    LT1 Guy
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    did this problem get resolved yet? running open manifold would cause a rich problem even with the o2 installed. when the car scavenges for air air gets pulled back up and the sensor sees i and thinks its very lean.

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    Pathelogical Liar BlackLT1Z28's Avatar
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    The original poster isn't running open anything. He just cut off his cat and now is running rich.

    Plus, a stock cam wouldn't allow for much to be scavenged and shouldn't cause a problem anyway. Unless there is a weak spring or valve float.

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    LT1 Guy
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    ok i missed what he had done. then i was reading about open headers so i figured you 2 knew something i didnt. he never posted bak up the codes. if the car is seeing rich then the o2 would have to be working its a high voltage code. if they werent or were not hooked up it would be lean low voltage or inactivity.

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    I went by the parts store 2day and borrowed there scanner and it showed i threw a lean left O2 senors 44 time, Shift light failure 91 times and an EGR failure 32times.

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