[Mp5ben]

I've been getting P0430 and P0420 codes, (inefficiency of cat) for both my left and right cat on my 05 WK with the 5.7

I've been quoted about $400 for replacement locally and before I have them replaced I want to find out what causes them to go bad! Mine are falling apart I'm pretty sure, I hear the particles popping against the pipes occasionaly and when I hit the muffler i can hear a rattle of stuff inside it.

My Jeep has 89k miles, pretty dang thorough maintenance records throughout its life and has always had crap gas mileage (14 city/hwy). I've owned this Jeep for about 3 weeks now.

So far I've replaced the spark plugs, oil, EGR valve, and oil pressure sensor. I've heard the hemi cycles alot of oil through its intake but when i took the resonator off, the throttle body looked quite clean. Could that much oil going out the exhuast ruin a cat? I would expect many hemi's to go through cats often if that is the case.

Thank you for any help!

 

[stephens039]

Might be bad downstream O2 sensors.

 

[Montreal300]

Could be the sensors but I find it odd that both sides would go at the same time. I had a fail on the #2 sensors on both sides at exactly the same time which I thought was suspicious. It was the PCM that was messed up. Both of the power supply drivers in the PCM had failed.

In this case, the cats would be suspect because the sensors are still registering. Extended idle times and very short trips in cold weather will foul a cat.

Oil back to the intake is through the PCV hose which is after the throttle plate not before it. Pull the throttle plate off and look inside.

 

[Mp5ben]

I will replace the o2 sensors with the new exhaust system so everything is fresh and reads right. Are there upstream/downstream sensors or are they the same part throughout?

When I talked to a local shop they said usually if the o2 sensors are bad they trip another code, and the p0420/430 codes are almost always bad cats.

 

[radioouman]

Cracked exhaust manifolds will cause the mixture to become too rich (o2 sensors detect too lean and computer makes the mixture richer) which puts unburned gasoline into the cats, overheating them. I just went through this on my Wrangler.

 

[tom19511]

A code P0430 may mean that one or more of the following has happened: The catalytic converter is no longer functioning properly An oxygen sensor is not reading (functioning) properly There is an exhaust leak

Read more at: https://www.obd-codes.com/p0430
Copyright OBD-Codes.com

 

[tom19511]

Unburned fuel or contaminants entering the converter, can cause the heat to rise out of control. These contaminants enter through the exhaust. Excessive heat can melt the honeycomb support. An overheated honeycomb may break and cause a rattle. It can also block the exhaust flow. This results in the exhaust being restricted. Restricted exhausts result in a loss of power, fuel mileage, overheating and usually a check engine light.

Common causes of contaminants entering the exhaust

Coolant, from leaking intake-manifold gaskets, is often drawn into the engine. A leaking head gasket has much the same effect. The chemicals in the engine coolant quickly contaminate the catalyst and cause failure. Promptly addressing any loss of coolant helps prevent this expensive problem.
Using the wrong viscosity of oil may also damage the catalytic converter. Heavier viscosity oil may produce more vapors. These vapors enter the intake through the PCV system. Partially-burned contaminants pass into the catalytic converter with the other exhaust. Unburned hydrocarbons greatly raise the converter temperature.
A bad oxygen sensor, dirty mass air flow sensor or an engine misfire will also allow unburned fuel to pass into the exhaust. This fuel burns in the catalytic converter.
Oil from stuck piston rings, bad valve guides, etc. also enters the exhaust. Oil consumption often results from extended oil changes. This reduces engine efficiency and the oil passing into the exhaust damages the catalytic converter.
Too many short trips at low speed can also cause the catalytic converter to fail. Converters need highway driving to reach operating temperature. This is how they clean and regenerate the catalyst. If we do not drive our vehicle often or far enough, the converter may fail. Vehicles that get only intermittent use commonly have this problem.

 

[Raffish]

I'm getting P0420..
New to me, '05, 5.7L WK, all stock,
Recently changed: oil, spark plugs, plug wires and boots, PCV, IAT sensor(old one was reading 10°C above ambient with cold engine
Doing soon: EGR, MAP Sensor, Fluids in - transmission +2 filters, x-case, both diff fluids,

I can get the magnaflow direct fit (p/n 24490) for ≈$600 CAD
I have tested with infrared thermomoeter( optical pyrometer) and its more or less the same on both sides.
Upstream 0₂ sensor (bank 1) readings look like normal sine wave, fluctuating from ≈ 0-1 V. Downstream holds steady at idle and is very erratic on acceleration.
STFT B1 bounces from about +15% to -15%
LTFT B1 ≈ -9%

I would like to figure out why I have a dead cat replacing it.

Thanks in advance for any thoughts..

 

[RCS1300]

Unburned fuel or contaminants entering the converter, can cause the heat to rise out of control. These contaminants enter through the exhaust. Excessive heat can melt the honeycomb support. An overheated honeycomb may break and cause a rattle. It can also block the exhaust flow. This results in the exhaust being restricted. Restricted exhausts result in a loss of power, fuel mileage, overheating and usually a check engine light.

The above is correct. Vehicle running too rich on fuel trims - from things like leaking fuel injector(s), bad egr valve, bad oxygen sensor(s), one or more cylinders not mechanically running correctly causing computer incorrectly to dump fuel into the other three cylinders in the bank., etc.

A v8 can misfire and you would not know it until a check engine light comes on. The check engine light comes on only if the misfires in any one cylinder exceeds 2%.

Before you spend the $$ on converters, have a mechanic put the vehicle on a scanner to make sure it is mechanically running correctly. Downstream O2 sensors functioning correctly, no misfires, fuel trims well within the normal range, and map vacuum in the 18-22 range at idle.

From your negative LTFT I would inspect a few items - fuel injectors for leaking, egr valve for sticking, and downstream O2 sensors for performing correctly.

 

[08rubie1]

If you dont need them dont put them back in... trying to find a shop that will take them out for you may be hard to find. i gained close to 1mpg after removing that cats in my 5.7 and another 1 mpg for a new header back exhaust. Letting it breathe better will help you in the long run.

 

[Raffish]

What would correctly functioning downstream 02 sensors V graph look like with a bad cat?
Does a cat fail completely at once? If not I would think a downstream 02 sensor would be unpredictable and tough to tell if it was working properly or not...

I am using a Panlong ELM 327 and OBD2 Car Doctor (Lite) btw

 

[RCS1300]

What would correctly functioning downstream 02 sensors V graph look like with a bad cat?
Does a cat fail completely at once? If not I would think a downstream 02 sensor would be unpredictable and tough to tell if it was working properly or not...

I am using a Panlong ELM 327 and OBD2 Car Doctor (Lite) btw

Q1. The waveform of the correctly functioning downstream O2 sensor looks exactly like the waveform of the correctly functioning upstream O2 sensor with a bad cat.
Q2. Do not know.
Q3. A correctly functioning downstream O2 sensor on a functioning cat will have a flat waveform.

 

[Raffish]

So how would you tell the difference between a partially functioning cat and a bad downstream 02 sensor?
I guess I could swap downstream sensors from bank 1 to 2 and see if the problem moves...?
Currently bank 2 downstream holds steadyish at ≈ .725V

Thanks

 

[wave_crusher]

I'm getting P0420..
New to me, '05, 5.7L WK, all stock,
Recently changed: oil, spark plugs, plug wires and boots, PCV, IAT sensor(old one was reading 10°C above ambient with cold engine
Doing soon: EGR, MAP Sensor, Fluids in - transmission +2 filters, x-case, both diff fluids,

I can get the magnaflow direct fit (p/n 24490) for ≈$600 CAD
I have tested with infrared thermomoeter( optical pyrometer) and its more or less the same on both sides.
Upstream 0₂ sensor (bank 1) readings look like normal sine wave, fluctuating from ≈ 0-1 V. Downstream holds steady at idle and is very erratic on acceleration.
STFT B1 bounces from about +15% to -15%
LTFT B1 ≈ -9%

I would like to figure out why I have a dead cat replacing it.

Thanks in advance for any thoughts..

You got a bad cat. The temperature should be higher on the output side of a cat. The chemical reaction that happens between the catalyst and the NOx in the cat creates head. The output should always be a bit higher, thought too much unburnt fuel causes it to create too much heat. And you burn out the catalyst

 

[wave_crusher]

So how would you tell the difference between a partially functioning cat and a bad downstream 02 sensor?
I guess I could swap downstream sensors from bank 1 to 2 and see if the problem moves...?
Currently bank 2 downstream holds steadyish at ≈ .725V

Thanks

Simple way would be to test the temps at the output of the cat and input.

You can swap the downstream sensors and see what changes in the computer

 

[Mp5ben]

Fwiw, my mechanic told me that p0420/p0430 codes are almost guaranteed cat failures...as opposed to o2 sensor failures.

I still think my Jeep's cats died due to the oil going through the engine and exhaust. When the original engine was replaced at 99k miles the mechanic said the manifolds were all still tight and no leaks to be found.

 

[wave_crusher]

Fwiw, my mechanic told me that p0420/p0430 codes are almost guaranteed cat failures...as opposed to o2 sensor failures.

I still think my Jeep's cats died due to the oil going through the engine and exhaust. When the original engine was replaced at 99k miles the mechanic said the manifolds were all still tight and no leaks to be found.

Of course a mechanic would say that certain codes are "almost, always" guaranteed to be the most expensive thing to replace on an exhaust system. Not saying the mechanic is a liar.....but they're all shaddy as slim is.

 

[PolkaPower]

Oil blow by is a big problem with these motors.
If you don't have an oil catch can on the pic return line then it's guaranteed that oil is getting back into the intake from this source.
Billet tech makes a nice can.
I bought a Mishimoto baffled can with a micron filter from Summit.
This is how much it had collected after 3000 miles.
I like this one because it has a drain valve on the bottom. There's nothing to unscrew

 

[Mp5ben]

Of course a mechanic would say that certain codes are "almost, always" guaranteed to be the most expensive thing to replace on an exhaust system. Not saying the mechanic is a liar.....but they're all shaddy as slim is.

That was just his experience in 30+ years. I trust the guy, and that shop doesn't even do exhaust work so not really any reason to lie.

Just throwing that out there to help

 

[Raffish]

Thanks all.
I have also heard that P0420 is unambiguous. (on this site as well as other sources)
I'd like to know what killed it though before I put another into a poor situation..
I got new intake gaskets and will be pulling the intake plenum to clean it shortly..
I'm sure it's as disaster, the TB was filthy when I pulled it..
I'll be getting catch can as soon as I can afford it...
She needs suspension too...:frown2:
New harmonic balancer going on this weekend...
225 K kms