[marlonbarksdale]

My mechanic told me its not safe to run a catless downpipe without the tune because will cause the car to run more lean. Is this true? I have a n55 btw

[n55david]

Originally Posted by marlonbarksdale

My mechanic told me its not safe to run a catless downpipe without the tune because will cause the car to run more lean. Is this true? I have a n55 btw

Not true at all.. you will get a check engine light etc

[fortythirtyfive]

I by no means have any technical evidence as to why it would, but here's my experience..

.. when I first ran a catless downpipe with a "mini cat" / spacer for the post sensor I had a few lean codes, the DME did appear to be trying to adjust because of that.

The car ran like sh*t, it began to stall when pulling away almost like it was choking. Ran it straight to an indie who could see live fuelling adjustments through logging. They advised me to run an adjusted tune if I really wanted to keep the catless DP.

Ironically MHD didn't suppress the CEL at first, although the other issues surrounding the DP did resolve for the obvious reasons. I still have their first emails somewhere with them stating they had no interest in removing the CEL with their tune.

A few months go by and a bunch of disgruntled posts online appeared to change their attitude around the subject, they added a DP checkbox and I've not seen a CEL since.

[n55david]

Originally Posted by fortythirtyfive

I by no means have any technical evidence as to why it would, but here's my experience..

.. when I first ran a catless downpipe with a "mini cat" / spacer for the post sensor I had a few lean codes, the DME did appear to be trying to adjust because of that.

The car ran like sh*t, it began to stall when pulling away almost like it was choking. Ran it straight to an indie who could see live fuelling adjustments through logging. They advised me to run an adjusted tune if I really wanted to keep the catless DP.

Ironically MHD didn't suppress the CEL at first, although the other issues surrounding the DP did resolve for the obvious reasons. I still have their first emails somewhere with them stating they had no interest in removing the CEL with their tune.

A few months go by and a bunch of disgruntled posts online appeared to change their attitude around the subject, they added a DP checkbox and I've not seen a CEL since.

It's cause of the spacer