Have a late 07 v8 vantage with 72k miles, high flow cats and AM power upgrade. During the summer months (NE USA) I would have emission light come on regularly coinciding with WTO jaunts. My obd stated inefficient cats most of the time with an occasional secondary pump fault. My initial thoughts and that of a few friends was that the cats were not getting hot enough to work with in the parameters dictated by the computer. (side note shell gas seemed to help this to a great degree) Now that cold weather has arrived I anticipated more faults, but it has actually abated! Does the computer adjust to outside temps and adjust it's parameters or is this a result of the colder air containing more oxygen and burning hotter and more efficiently. Power generation seems higher, bringing me to my second query; Has anyone else noticed the rear of their car becoming more squirelly in the colder weather? Or could it be something has changed the geometry of my car, being at 70 K miles, last alignment being mid summer. Any input would be appreciated. BTW, love this car and I can not drive it enough, just am annoyed now by the jumpy rear end has become.

 

Not sure about if/how the computer adjusts for outside temps, but the cold will definitely make your back end feel more loose. Tires need to be warm to be sticky for traction, cold tires AND cold pavement make that more difficult.

And kudos on the mileage! I've only got 46k lol

 

^^^ Thanks, have PSS and love. Noticed car has a hop when lifting throttle even in a lane change. I am also in an area with rutted roads grabbing the wide tires. I think I will experiment with the same location under varying conditions where the looseness seemed most pronounced. I wonder if the computer accommodates/compensates for temp changes in fuel delivery.

 

High Performance Summer tires (PSS) don't give "great traction" in temps below about 45-degrees F. And this gets even worse at lower temps.

 

2nd the temp for the tires...

As for the cats, you stated there high flow meaning aftermarket. The code you have means the cats are not filtering the gases to lesser harmful gas..

This is common on all highflow catalysts for any make and usually triggers a dtc when hot..

Solution, either change back to stock cats or get a tune from places like Velocity..contact Stuart and I'm sure he can hook you up

 

that's a bit of an unfair generalization to make imho. I'm sure any responsible aftermarket company specifies cat with precious metal loading to at least not ping p0420/430 if not comply with in market testing at best.

we comply / don't have dashboard errors, as im sure popular vendors on here do too, so to tar all with same brush as those makers who leave consumers with error lights after an 'upgrade' is wrong of you.

the advice should be, make certain future buyers buy from supplier who gurantees no error lights or provides ecu tune to counter.

but yes and for this poster,you are right. And if anybody has a set which do ping errors, a cal to overt dtc will work. but shouldn't the supplying cat vendor have duty to customer to correct? Of course, unless cats not for road use or sold informing will have error lights

 

It's not unfair, it's just a true fact I've made not masked. I have no reason to lie or talk B.S on these forums..

I've never seen your products this side of the sea side so I can't comment on your products personally..but it is logic, if your not pushing enough less restricted gases through then its not really a highflow, if anything its just considered more flowing than stock, that's all I can agree with you on...being there us no such thing as a mediumflow, guess anything more than stock is highflow

I understand there's no law/rule on specs for gases that flow through the catalyst to be considered a highflow, only specs on what a stock catalyst from the manufacturer should perform as duty, so really it's all marketing as to which the client will buy, dyno numbers over stock and compared to other brands is always good brownie points I guess..

I know you won't agree but it's cool..in my mind it's like making a cold air intake on your car and sticking a Fram replacement air filter paper element on the end..it does allow more air through the system than stock so did I just create a highflowing cold air intake? Obviously not but at that point your just playing with marketing.....just saying as a client you always need to research what your buying

 

As stated above, performance tires are bad below 7 C or so, pretty much becoming hockey pucks. Unless you have driven over some really rough roads or hit some bad bumps I would imagine an alignment done in the summer would still be OK.

 

I surely have no clue what you are getting at regarding pretty much everything you say, but i think from what you write my confusion is because you are mistaken exactly the triggers behind p0420 / p0430.

You are correct that the fault codes are triggered because of insufficient gas conversion of pollutant into harmless gasses, but this is SOLELY due to insufficient precious metal loading applied to the surface layer of the the cat (google 3-way catalyst), and nothing to do with the flow capability of any particular cat. The only other reason could be perhaps when new the precious metal loading was sufficient enough to keep ECU diagnostic system happy, but cat has since been contaminated and destroyed and will no longer convert. Leaded fuel for example will poison a cat and render it useless.

Example, if we were to take the stock factory cat with its restrictive matrix with NO precious metal loading applied, it would fail emissions and ping p0420 / p0430. If we were to take a 100 cell cat loaded to the teeth (beyond what is cost feasible) with precious metal content, the 100 cell cat would now likely pass emissions and not ping error codes, beating the high cell density factory cat with no precious metal - Get it now?
Meaning it has nothing to do with "pushing enough less restricted gases through" and everything / the only thing to do with precious metal loading. So when you made the generalization that all aftermarket cats ping errors, then no! it depends on precious metal loading specification, nothing to do with how restrictive it is / isn't, and is therefore something you cant really comment on because you don't know how each vendor specified precious metal loading.

The thread / OP was in search of technical reason why the error light was on the dashboard. The answer is that for the cats fitted to his car, the precious metal loading / content is insufficient to keep ECU diagnostic happy. The purpose of any internet forum is to inform and the advice is, if owners want to upgrade car with high flow cats and cant tolerate error lights, make sure the vendor states the cat is loaded sufficiently with enough precious metals to keep happy the cars diagnostic system. If diagnostic system is unhappy, a remap must be downloaded to counter, but in my mind, an ECU reflash is an integral part of upgrade to high flow cats anyway - to ensure 'belt and braces' that no dashboard error lights, ever, occur. I'm sure all vendors as I, simply cannot tolerate a customer having dashboard errors after an upgrade.

Another point you seem confused on is the power gain from a higher flow cat. More-or-less, any makers cat will perform exactly the same as any other. Its not rocket science its simply about removing a high cell density cat and replacing with lower cell density variant. What governs power increase is the rule of back pressure reduction versus power increase, and is a constant nobody can really influence to be any other / better. For the V8, about every 5KPa reduction in backpressure a 3.5 ish BHP rise will be the resultant. No matter who the cat maker is the backpressure reduction will be about the same, so then will the power increase. What will separate the vendors will be precious metal loading of the cat, and to a degree the ECU tune to go with high flow cat to enable best possible power.

Get it all now?

 

As I understand it, please correct me if I'm mistaken:

Irish's point of view is that the computer will know that not enough exhaust gas is being converted by aftermarket cats because there is less catalytic material, IF all things are equal regarding the quality of the material.

Mike's point of view is that the computer won't know the difference between a high-flow cat and the original cat IF the quality of the catalytic material is good enough.

In my opinion, both of you are absolutely correct. However, the difference in opinion is that nobody (at least that I've ever seen in the last 15 years of me tinkering with cars) discloses the quality of their catalytic material - only cell count. So it's impossible as a consumer to know which aftermarket cats are going to have the best catalytic material.

Some info about cats in general:

The quality of the catalytic material is based on precious metal loading (precious metals are literally that: platinum, palladium, rhodium, and gold). The more precious metals, the better the cat converts exhaust gas to less-harmful exhaust gas. However, these metals are extremely expensive, so there's a balancing act between efficiency (more precious metals) and cost (fewer precious metals).

Our cars have two O2 sensors per catalytic converter - an upstream sensor (pre-cat) and a downstream sensor (post-cat). Each sensor measures the exhaust gas, and the computer looks at the difference between the two measurements. If the difference isn't great enough, the computer thinks the catalytic converter isn't doing a good enough job of converting the exhaust gas (the more gas is converted to less harmful gas, the greater the difference between the two measurements would be). When this happens, it triggers a fault code for cat inefficiency - p0420/p0430 (same fault code, the difference in the number tells you which cat isn't efficient enough).

Most OEM cats are in the 400-600 cell range. Most aftermarket cats are in the 100-200 cell range. So, most aftermarket cats can be considered high-flow. Good, concise explanation I found about cell counts in cats: "200 cell is 'cells per square inch', ie 200 holes in the ceramic brick per square inch. The lower the number, the bigger the hole so the lower the back pressure. Lower cells also make it less efficient at its function so no OE cats are 200 cell. They are 400-600+ cell."

 

if you piece together the info you posted you can end up at the answer, which is not subject to any opinion, is how these things work.

lower the cell density the lower the overall surface area in total to layer with precious metals. If there is a 600 cell cat with half the loading of a 300 cell cat (roughly but not exactly, but good enough for this arguement) the cats will convert the same. Keep the pcodes happy.

however, the statement "Lower cells also make it less efficient" is incorrect if using above example because each different cell and loading strategy achieved the same end result. Its just a more-than-likely case the higher cell less precious metal route was cheaper, hence the chosen OEM route.

so in aftermarket if the cat efficiency code wants to be kept silent, a heavy precious metal loading is needed, and its as simple as that.

 

There were two parts to the OP's question, the second part was: "Has anyone else noticed the rear of their car becoming more squirelly in the colder weather? "

The answers to this part were somewhat buried in other responses but the answer, as mentioned above is "Below 7-degrees C, about 45-degrees F your tires become about as hard as hockey pucks"

 

Get O2 spacers for the rear secondary oxygen sensors and that should cure your problem. It pushes the sensors outside the exhaust stream and restrict how much air can get to the sensors.

The Ken Harrison cats come with these fully embedded welded in so they never had that issue. Smart clever design.

 

great news, so it would seem upgrade cats that trigger cel for Aston are in minority, and for those that do where ecu tune is not available, a low cost work around cures the problem

 

Ya the main reason you are getting "inefficiency code" is the ECU is comparing the primary oxygen sensor data with the secondary oxygen sensor data. If the ratio/spread is too narrow then it thinks the cats have failed and are not doing their job. You should never touch the primaries since these are critical to ensure proper air fuel ratios and etc, so you have to minimize the reading of the secondaries. You can trick the ECU into thinking the cats are fine by simply pushing the secondaries out of the way to help widen that ratio/spread enough to where it does not trip a code.

Simple yet effective solution