Measuring Exhaust Backpressure - VZ Alloytec190 2005

[ForestVt]

Measuring Exhaust Backpressure

(procedure obtained from Tuner. university. com)
"If you wanted to find the back pressure being caused by the catalytic converter, you simply plumb in the fitting
before the cat, do a WOT run and find the peak pressure. Then you come back, switch to the bung behind the
cat, and do another run. You should then be able to see the difference between the two."

I ran this in my VZ 2005 - exhaust catalysts never replaced - Odometer 245.500km - Alloytec 190 (In Brazil named Omega CD).

Note: In my VZ, I did not observe evidence of problems related to obstruction of catalysts. I present these data as a reference for possible use in diagnostics and, if appropriate, obtain critical comments from experts. I thank you in advance.

The results follow:

Pre-cat-left hand side
3000 rpm = 10 mbar = 0,14 psi
WOT = 110 mbar = 1,6 psi

Pos-cat-left hand side
3000 rpm = 2 mbar = 0,03
WOT = 50 mbar = 0,7 psi

Pre-cat-right hand side
3000 rpm = 10 mbar = 0,14 psi
WOT = 110 mbar = 1,6 psi

Pos-cat-right hand side
3000 rpm = 2 mbar = 0,03 psi
WOT = 50 mbar = 0,7 psi

This is it.

I just hope not to have to replace the catalysts of this car. In Brazil simply "does not exist" for replacement. (Original part for Holden Commodore VZ 2005).

Thks.

 

[vr304]

What are the emissions laws like in Brazil? U could remove the cats altogether and replace them with a straight piece of pipe as a lot of people here in New Zealand do otherwise u can get higher flowing performance cats from the likes of eBay

 

[ForestVt]

In Brazil, in practical terms, only the trucks and other vehicles converted to use Natural Gas are periodically subjected to inspection "strict" (and impeditive) referring emissions. To be honest, this question depends on much more than the owner's sense of responsibility than the law enforcement effect.

On the other hand, I thought that if you eliminate the catalysts, there will be failure indication by the ECU (DTC).
In this VZ I even keep there are two sensors (Wideband - before catalysts) one on each bank of cylinders. There are also two sensors O2 (Narrowband - after the catalysts) one for each bank of cylinders.

My question is: There is some monitoring algorithm of the catalyst performance that handles the two signals - the signal obtained before the catalyst and the signal obtained after the catalyst?
If any; the elimination of the catalytic action remains transparent to this algorithm?

Now I'm very curious ...

 

[Not_An_Abba_Fan]

That result is expected for factory cats. ALL cats restrict exhaust flow to a degree. High flow cats increase engine performance because they have the least amount of restriction (back pressure).

The pre cat sensors measure engine efficiency and allow the ECU to adjust fuel trims as necessary. The post cat sensors are a reference signal to check the efficiency of the cat. They should be fairly static in their voltage. If they start switching like front sensors then the cats aren't working. Some manufacturers also use the rear sensors to adjust fuel trims to compensate for a cat that is on it's way out, not sure if the Holden do this.

The only accurate way to test to see if a cat is working is to do a temperature test. Get the car to operating temperature, drive it hard for a few minutes, stop and hold the revs at 2500 rpm, then using a laser thermometer measure at the front of the cat and then at the rear of the cat. It should read at least 10% hotter at the rear. If it is hotter at the front, the cat is blocked, if it is pretty close both ends, the cat isn't working, if it is hotter at the rear, it's fine.

 

[ForestVt]

not_an_aba_fan, thank you for the clarification. I'll check the catalysts as soon as I get a laser thermometer borrowed.

Despite the focus of attention is the catalyst, and to have awareness that are important elements in the most responsible context, I still wonder if simply removing these allow "normal" engine operation - specifically in this Holden VZ Calais, Alloytec 190, LY7 engine (without direct injection).
I believe in the ECU, there is active restriction of performance - aiming emission control - in case of failure detection of the catalyst.

If some of the friends can confirm that this is indeed, thank you in advance.
(I try to get smart! In some past events, "it was me" who diagnosed undetectable failure reason for "trained professionals" on call here.
:hmmm

 

[kiwicon]

Take cat out, smash out centre ceramic, put cat back in

 

[Not_An_Abba_Fan]

Engines are all built for performance. They are "de-tuned" to meet emissions standards set for the year of manufacture. If emissions standards didn't exist, engines would be tuned for maximum performance (including fuel economy). Every engine runs the same way, fuel, spark and compression. It's the way that the ECU controls the fuel and spark as well as external components such as catalysts, that will determine the engines ability to meet the standards.

So yes, in short, the ECU is tuned to meet standards so in turn, restricts performance. A car does not "need" cats to run efficiently, they are ONLY there to meet emissions standards. Same as the exhaust, it is only there to meet standards. The best exhaust for maximum performance is tuned length headers. It's not practical to run open headers though, so the exhaust is a necessary evil. Remove the cats and get the car tuned and you will certainly notice a decent improvement.