Catalytic Converter Problem?

Mopar Exhaust Systems

  1. JTG

    JTG Well-Known Member

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    Hi, I'm running dual Catalytic Converters on my 68 Cuda, I have a noise coming from the vehicle that sounds like a rattle snake or like someone shaking an empty can filled with sand or very small stones, I believe one the converters is on its way out, would you folks agree based on this symptom. Thank You
     
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    • Syleng1

      Syleng1 Karma is real and Life is short... FABO Gold Member

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      I’m going to ask a silly question:

      WHY are you running a cat on a 50+ year old car to start.

      but to answer your question- yes sounds like a broken up cat
       
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      • 1969cuda

        1969cuda Well-Known Member

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        Great question.
         
      • JTG

        JTG Well-Known Member

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        Syleng1, not a silly question, I'd be asking the same thing. I'm a double lung transplant recipient, had the cats installed to help lessen the fumes for health reasons, wasn't an easy decision to make at the time to have these installed on a car that would never have them in the first place, there the high flow ones so not very large in size, but they did lessen the fume smell dramatically, way more then what I ever expected.
         
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        • Ccas

          Ccas FABO Vendor FABO Vendor

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          If the cats were ceramic style universal and your car had any kind of condition that made it run lean and hot for a bit, the brick could have broken up. It's quite common in ceramic cats.
           
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          • JTG

            JTG Well-Known Member

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            The cats I'm running are from Vibrant Performance Gesi HO Series Part# 7525, the problem happened after driving on the highway for 28 miles at 60-65mph.
             
          • RustyRatRod

            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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            Just to clear up a little myth....there's no such thing as a "high flow" cat. That's all marketing hype. Every bit.
             
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            • Bodyperson

              Bodyperson Pedal to the metal FABO Gold Member

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              I have to think it has to do with dwell in the chamber. There aint no free lunch.
               
            • Syleng1

              Syleng1 Karma is real and Life is short... FABO Gold Member

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              Okay- that is a really good reason. You are lucky to be here and taking precautions are good to protect your gift.

              So honestly- running cats on cars not designed for them is no easy feat. Maybe investing in a fuel injection system or a power train that runs a lot cleaner to begin with is a better choice. You see the raw fuel on decel with a carb can load up in the cat and then when you accel it burns so hot and fast it can damage the cats. A fuel injected vehicle controls this process like a thousand times a minute to maintain the perfect (well sort of) exhaust burn. Also protecting the cat. The way the cat works is it absorbs oxygen to help “reburn “ the exhaust flow but needs the cycle of oxygen storage and then release, oxygen storage and release. With out that flow the cats will be damaged.
              So there is not one cat that can easily handle this without the oxygen flow. Early GM cats were removable pellets (balls) that could be replaced - trust me I did my fair share as a gm tech in the 80’s. They would melt together and became a clog because of feed back carbs not being able to control the oxygen flow properly so they added o2 pumps or air pumps to engine to help add oxygen to the exhaust stream to supply the cats with enough oxygen flow. All of that with carbs. The first fuel injection set ups for emissions reasons helped but wide open throttle still created cat overheating due to the lack of O2 in the exhaust stream.

              Anyhow- all I am saying is your engine is causing the damage because it was not designed to handle what the cats need. So change the system (aftermarket fuel injecting, modern motor, or add an air pump system like off a late 80’s van ) to protect the cats. Otherwise uncontrollable rich and lean conditions will cook the cats very quickly. I also want to add that the info I am giving is over 35 years old from my head. Go and start looking up info on engine carbureted with cats from the 80’s. You will find better more detailed info than what I remember from that time frame of my life. Look up How a cat works first to understand what you are dealing with. You may have a lean condition (too little fuel) so there is lots of oxygen in your exhaust stream or too little Oxy from a rich condition. The cat needs the cycle of rich to lean back and forth to work properly.
               
              Last edited: Jul 12, 2021
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              • JTG

                JTG Well-Known Member

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                Thanks Syleng1, your telling me what I already feared, in other words make some changes or be prepared to be replacing cats on a regular basis.
                 
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                • Ccas

                  Ccas FABO Vendor FABO Vendor

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                  Quite possibly. However, it could be a borderline situation. If you were to replace the cats with a metallic substrate instead of ceramic, they can handle a LOT more heat without coming apart. So if you are not in a position to do a lot of trouble shooting right now, want to be safe and want to drive your car now, I would suggest upgrading to a metallic substrate version to get going again and then take your time and troubleshoot the root cause.
                   
                • 1971 CY Dodge Dart

                  1971 CY Dodge Dart Dart Swinger FABO Gold Member

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                  Aftermarket high flow cats have a smaller cell count than OEM cats thus making them high flow AND more likely to blow out over an OEM one.
                   
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                  • RustyRatRod

                    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                    You cats can hit the disagree all you want. That's the truth. There's no such thing as a high flow cat. They only advertise that because they make the inlet and outlet bigger than a stock production cat. Unless you enlarge the exhaust to the cat's inlet and outlet size, you don't get the "high flow" effect. Converter material is restrictive. That's how it does its job. I'm not even going to point to the THOUSANDS of links to articles online that verify this. Yall have the same internet I do. Just remember one thing when you want to disagree. I'm not selling products. I don't have a dog in the hunt. Believe what you want. A fool and his money are soon parted.
                     
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                    • RustyRatRod

                      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                      You keep drinkin the kool aid.
                       
                    • 1971 CY Dodge Dart

                      1971 CY Dodge Dart Dart Swinger FABO Gold Member

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                      One more point about high flow cats since I've been tuning on late models with HP Tuners for many years. When you replace an OEM cat with an aftermarket high flow cat more often than not your car will throw a CEL due to the smaller cell count. We used to just turn off the monitors in the PCM to get around this but things have changed with emission tests.
                       
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                      • Ccas

                        Ccas FABO Vendor FABO Vendor

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                        Correct. We've done numerous dyno tests on this subject. And just to add and clarify... the high flow cats do not do as well emission wise. The less cell count, the less effective they are. Because of the lower cell count, you can't get as much platinum and/or Palladium in those bricks. Hopefully this thread doesn't get jacked because of this but a similar analogy would be with high flow performance mufflers vs oem mufflers. When you replace your OEM mufflers with performance aftermarket, you get higher flow but you also get unwanted drone and resonance. As with most good things in life, you can't have your cake and eat it to. :)
                         
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                        • pishta

                          pishta I know I'm right....

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                          My son lost a coil on a 1UZFE (Toy/Lexus DOHC V8) and all that unburned fuel from the left bank went right into the cat where it burned and turned the substrate into charcoal thats bouncing around in there now. Same effect, sounds like a rattle when accelerating or decelerating. Gonna pull it this weekend and try and dump/suck the chunks out with a shop vac. internet pic
                          ?u=https%3A%2F%2Fbmmuffler.com%2Fwp-content%2Fuploads%2F2017%2F08%2Fimg_0894.jpg
                           
                        • RustyRatRod

                          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                          Nice.
                           
                        • RustyRatRod

                          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                          So you blowin some bullshit isn't jackin the thread? My point is really easily verified with a ten second internet search. Maybe your suckmuffins will keep buyin your bullshit, but I don't.
                           
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                          • 1971 CY Dodge Dart

                            1971 CY Dodge Dart Dart Swinger FABO Gold Member

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                            I don’t need an internet search as I have first hand experience here. It’s okay for you to be wrong. :)
                             
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                            • RustyRatRod

                              RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                              Hey it's all good. You have one opinion and I have another. I can agree to disagree. You ain't cornered the market on experience, either.
                               
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                              • JTG

                                JTG Well-Known Member

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                                Thanks Ccas, I just ordered a couple of Magnaflow metallic substrate converters and I'm going to do exactly that, get the car running as it should and then investigate the problem later. If my car is going to be eating converters at least the Magnaflow Converters are way cheaper then the Vibrant Performance ones so it won't be so painfull in the wallet. I have a high lift cam in the car so I'm running Lucas Hot Rod & Classic High Performance 10w40 motor oil with the higher zinc, also running Ultra 94 in the gas tank, do you think this may have contributed to the Vibrant converters failing over time or was it due to driving on the highway with the 3.91 in the back where the car is running at higher rpms at 60mph and generating more heat. I know most folks don't run cats on this type of application but for those of us that do what is the average life expectency of a converter, a regular daily driver I believe is around 100000miles.
                                 
                              • AJ/FormS

                                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                                I know you might not want to hear this, but if your exhaust is stinky with a high-lift cam of less than 250*@.050 (the biggest I have tuned) then, IMO, the tune is off. Depending on when it is stinky, it could be the T-port synchronization, and or the timing, and or the fueling.
                                At 65=3050@ zero-slip, perhaps 3150 on the tach, your iron headed 360 will be wanting at least 50 to 56 degrees of timing. An alloy headed 360 might be asking for up to 60*
                                If you do not provide the lead, the fuel-charge may not finish burning in the chamber. With "late timing" the potential for max pressure does not occur. Instead, the expanding gasses chase after the piston, on the power-stroke, putting heat into the cooling system thru the cylinder walls. This destroys scavenging, and may drive hot exhaust up into the intake instead. The Mopar 292/292/108 for instance, has 76* of overlap. That is a lot of time for both valves to be open at the top of the exhaust stroke. By 3000rpm, the expanding gasses should NOT be wanting to go up into the plenum, especially not with headers. But the exhaust valves will not be "closed " until perhaps 30* ATDC, so who knows what goes on with late ignition timing. With log-manifolds, and late timing, anything can happen.
                                But you know, I had a 223/230/110 cam , a hi-lift .538/.549 cam in my 360 for several years. That I ran at 60=2680 with 27" tires (manual trans). At cruise, it liked 60*of timing advance with alloy heads. I could not get that out of the factory distributor, on top of the Power-timing, so I bought a stand-alone, dash-mounted, dial back, timing delay box to make up the difference.
                                What I'm suggesting, is that if you clean up your cruise-exhaust, your Cats may be going along for a free-ride..... at cruise at least.
                                 
                              • 448Scamp

                                448Scamp Running Free

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                                You need to find a different oil. You need a Cat safe oil. The high zinc content in that oil is hard on the Cats. No matter how well your rings are sealed there will be some oil migration into the exhaust system. I don’t know if Lucas makes a Cat safe oil but you should find one. I know I killed several Cats on early 2000’s GM garbage and it was quick because those things had horrible ring seal.
                                 
                              • JTG

                                JTG Well-Known Member

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                                Hi 448Scamp this is the catch 22, I been trying to figure out what oil will have enough zinc for the 520 lift cam but not too much where it will be problematic for the cats, maybe someone can provide a recommendation.
                                 
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