I made a mistake - Decatted JK.

**Butch Dassie** · 2021/03/08, 05:50 PM

Thanks for the feedback.

With the cat deleted, the ECU must have thought a DPF regen would sort the trouble code, which results in over fuelling. With less back pressure, you should have been scavenging the chambers better resulting in it running leaner. However, you have confirmed that wasn't happening.

Just telling the ECU not to regen (no DPF / cat) should have sorted the fuelling.

With petrol motors, you have to get the stoichiometric mix right.

**HeinrichC** · 2021/03/11, 05:34 PM

Originally Posted by Butch Dassie

Thanks for the feedback.

With the cat deleted, the ECU must have thought a DPF regen would sort the trouble code, which results in over fuelling. With less back pressure, you should have been scavenging the chambers better resulting in it running leaner. However, you have confirmed that wasn't happening.

Just telling the ECU not to regen (no DPF / cat) should have sorted the fuelling.

With petrol motors, you have to get the stoichiometric mix right.

a DPF on a petrol engine?!?

**Butch Dassie** · 2021/03/11, 05:42 PM

Originally Posted by HeinrichC

a DPF on a petrol engine?!?

Quite correct - not on this old a vehicle, but Europe is installing DPFs on new petrol motors.

Still, the ECU must have thought it could correct the missing cat trouble code by over-fuelling - not so?

**HeinrichC** · 2021/03/11, 07:23 PM

DPF is an acronym for Diesel Particulate Filter, you would struggle to fit it to a petrol engine. You must be referring to a PPF

**Butch Dassie** · 2021/03/12, 08:10 AM

...or just PF for both SIC and CIC motors.

**JCMostert** · 2021/03/12, 08:28 AM

On a different note:

What harm can come from decatting a vehicle?
Is it advisable?

**Butch Dassie** · 2021/03/12, 08:42 AM

It's not so much that de-catting can harm a motor; it's more about the design and tuning of the motor.

Cats are anti-pollution devices. The trouble is that they eventually clog up and can then cause harm to the motor. De-catting is usually much cheaper than buying a replacement cat.

Especially petrol engines are designed with a certain amount of back-pressure. Changing this can increase fuel consumption and can actually lower your power. See anti-reversion exhaust manifolds.

Thus, the OEM ECU monitors for the presence of a cat. If you do a cat delete, you need to tell the ECU not to look for it. In this case, the fuel map also needed to be tweaked as it was over fuelling. Conversely, running too lean can put a hole in your piston.

Done properly, de-catting can improve your fuel economy and power.