high flow cats + CELs

Here is a question directed to 355 Owners only;,"Why are you putting on High-Flow Cats to begin with?"

 

In my case one of the OEM ones was rattling around inside like a castinet. Shopping for replacments hyperflows were recommended by a well known tech to me.

 

Mine came with them on and when I switched them my car sounded like a hondararri so I went back to hyper-flows. Sounds great again

 

Yes, I understand replacing a cat for those kind of reasons, but why are you putting on what is called a "high flow rate" cat?

 

Sound?.......Can you get beyond that superficial aspect for the time being and tell us your reasoning for high flow cats based on engine dynamics pertaining too fluid flow exit(exhaust).

 

I am getting low cat efficiency codes, and I have narrowed it down to failing OE cats. I dont want to spend the money on OE, so I am going aftermarket.

I haven't seen any "low flow cats" offered.

 

Have you pulled them off the car and examined them?
If they have never been changed(1996) and are OE they are ceramic core. Are they broken? Are the honeycomb's clogged?

Are the ceramic core OE and metallic core OE the "high flow" type?

 

Like I said they came on the car...I wasnt going to spend the money to go back to OE like Ernie said.

 

Because DH told me to. It was not a glowing recomendation but more of it's probably the best option out there. (Hyperflows)

The exhaust note is richer with them and as I said I don't get CEL and no extenders.

 

According to my service history they were replaced with OE at 12K miles, long ago. Actually, the cats appeared in good shape (only looking from the rear) when I had the exhaust off earlier this year. So, I am going to remove the cats and look again. I will have the new cats on hand if I decide to go that route.

I dont know anything about the flow type of the OE ones.

 

My car had the Fabspeed headers, Nouvalari cats and mufflers installed when I bought it.
Did not get any stock parts with the car.
I feel I just need the source of the now CEL P0133 and P0139 codes which pop up as BOTH on the driver's side (bank 1) sensor #1 and #2.
... and curious about the P0422 and P0432 codes before the L shape extenders were installed ?????
I am confused.

 

The reason I asked the question in Post #51 was to get you thinking of why you do what you do...LOL
....and the reason for limiting this discussion to the 355 is because there is something very unique about it which is different than most any other car you've owned.

You've heard of the move, "Godzilla vs Rodan"?...well how about this:

EPA vs Ferrari Race Engine

Here is an excerpt from an email I sent to an FChatter awhile back...

"The 355 engine needs a little back pressure at lower rpms to help bottom end torque and the exhaust flow needs time in the catalytic converter to properly process the hydrocarbons so the post cat O2 sensor sees the correct result and sends the necessary data back to the engine control module when it is operating in closed loop mode. This is where the factory OE cat shines..it accomplishes both of these requirements.

The high flow cat does not allow enough time(relative to cell density/count/surface area) for the hydrocarbons to be completely processed and the post cat O2 sensor detects this inefficiency and the data transmitted to the ecm causes a pending code which by the design of the software protocol eventually posts a check engine light with multiple fault codes. This type of cat also does not produce the back pressure which IMO is needed for a street car(racing is totally different). An interesting point to be noted is that some people have installed the same high flow after market cat.......some get a CEL immediately, others get a CEL miles later...and some get no CEL's.......all of this is totally dependent on fuel metering efficiency, combustion efficiency, and overall mechanical condition of each individual engine on which these cats are installed. Might as well include the wiring harness,sensors,etc. At least you can see the many many variables involved.

Now you have some idea of just how unique the 355 is with its' primary and secondary exhaust systems. Primary exhaust for low demand in power(low rpms), and which satisfies the EPA requirements(closed loop ecm mode), and the high power demand(high rpms) which opens up the by-pass valve and allows almost complete flow of exhaust gases thru a basically non restrictive and unmonitored(open loop ecm mode) secondary exhaust.

Please note,the life expectancy of any catalytic converter, regardless of core composition(ceramic or metallic), is totally dependent on fuel metering efficiency and combustion efficiency", provided there is no excess introduction of oil from worn rings,valve stem seals,etc., and no introduction of harmful chemicals thru the air intake system".


Hate to use YouTube Video's but in this case it may help those who are unfamiliar with the operation of cats and O2 sensors.

https://www.youtube.com/watch?v=nJ0G01nlFRo

If there is an upstream problem that caused the cat or O2 sensor to fail, replacing with new components/parts will also fail like the ones before if the upstream problems are not addressed.

Cats are not designed to be overloaded with a superabundance of HC's and other crap.....they work well to clean up the exhaust within certain parameters.....overload them and it will eventually lead to a catastrophic failure.

Feel free to comment on this post as I am not a street car/EPA expert.....my expertise is with full blown race engines that aren't restricted by governmental bs.

 

Here is a summation...

"High Flow" cats are great for single exhaust system cars(almost all cars are like this).

There is no need for this type of cat on a 355 which has two exhaust systems.....any regular cat that is properly sized will be sufficient....do not pay a premium for a "High Flow" type, that is a waste of money.

Another interesting twist on the 355(5.2) which is not like most cars(especially of its era) is the post cat O2(lamba) sensor's output can be used by the ecm/ecu to adjust the fuel/air ratio......how that effects the engine when you remove it from the exhaust stream with extenders or remove and use a simulator I will leave it up to you to determine.

As for sound?......you have the perfect set-up on the 355 for the personality of a "Dr. Jekyll and Mr. Hyde". The DR J side is all about the Stoichiometric Calculations for its' EPA master...a little on the tame side, but do a WOT or kick it past a certain rpm speed and it is no holds barred MR H that lets out an F1 scream all the way to the speed limiter. It doesn't get any better.

So unlike the single exhaust systems where one puts on a "High Flow" cat to improve performance and then has to walk a thin line and do a balancing act to prevent CEL's, the 355 can use a regular cat that doesn't throw a CEL and when you need performance(top end) it just kicks it up to the secondary unrestricted exhaust system.

Hope this gives you a better understanding of how your 355 works.

 

Enzojr ...... when you are cruising in high gear on a cool day/evening ..... how low does your coolant gauge read?

use this diagram and indicate a number on your response;
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Goth that gauge stays right around the #10, occasionally notice it at #9.
That gauge has the least movement of any of them.
I will check it in the next few days heading toward the coast, I don't often check it in 6 th during a cool cruise.
But I will now and get back to you I might be surprised.

 

Yes Enzojr, definitely check the gauge on a cool hwy cruise in 6th .... and report back ....

 

I run straight pipes and have no CEL.

Kai

 

Everybody knows you drive a 348, to one inch of its death. No CEL for you.

 

Thanks- great write-ups!

I'm going to ask another question regarding remote controll bypass valves in a different thread...

 

Should get this "test" done on Sunday or Monday, we actually have rain for the next two days. I know the car won't melt in the rain but hate cleaning up the mess after
Also that will give me time to re read your link from 2012 a couple times.

 

The car is afraid of throwing a CEL

Lol.

Kai

 

Gothspeed
Conditions were 63 degrees, 45 min drive, covered 35 miles. Flat hwy in 6th gear at about 60mph. Per your graph above it never went lower than between 8-9 on your scale. Once on the hwy is stayed pretty much right there.
Anything ?
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Side note, normal driving I am usually straight up 190 degrees or a #10 on your scale above

 

Ok Enzojr, thanks for posting ....... your temps are in the good zone ..... which is a very important thing .... ..... however going back and looking at your pic on post #28, I noticed that your cats have a rather big splice right near the post cat o2 sensor ....... this splice would allow ambient air to enter that area ...... I am thinking this might contribute to the symptoms you are experiencing ...
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