NewEdgeStang00

I just had an o/r MAC ProChamber h pipe installed, with my previous super 40 series american thunder catback. The car has a very strong exhaust smell coming through the bottom of the car, from the manifold area during idle. It's actually bad enough that it's like gassing myself in a garage. I do have an SCT SF3/x3 flash tuner since I had 4.10 gears put in. I was told since the cats were deleted I'd be running rich.

So I was wondering how I can adjust these parameters myself with the SCT tuner? There is only a WOT Air/Fuel ratio where I can adjust to make it .6% (increments) leaner or richer. However, it's under WOT category so does this mean this will affect the air/fuel under WOT or will it affect me under idle too?

I just needed some input from you guys before I start making things worse

cliffyk

That is not true, neither the cats or the rear O² sensors have anything to do with engine control. The MAF, ECT, IAT, TPS and front O² sensors do--but not the cats.

Two things come to mind however, any new exhaust component will stink as it burns off the manufacturing lubricants and coatings--and having no cats will make the exhaust stink.

If there actually is "very strong exhaust smell coming through the bottom of the car" then you have an exhaust leak--which can make the engine run rich if it is before or near the front O² sensors.


The exhaust flow is not one homogeneous stream, but rather a series of pulses created by each exhaust event. These pulses have a head, body, and tail; each with different characteristic, with their pressure relative to the outside world being the most significant.

• The head is at a pressure higher than ambient, when it passes the "leak" the gas flows out into the world; but the chemical composition of the gas in the pipe remains unchanged;
  
  
• The body is at or close to ambient pressure. When it passes the leak nothing happens as it and the ambient pressure are nearly the same--the chemical make-up of the gas in the pipe remains unchanged;
  
  
• The tail is at less than ambient pressure (nearly a complete vacuum), and when it passes by the leak it sucks in ambient air--changing the exhaust gas chemical composition and making it appear "leaner" to the O² sensor;

This makes the PCM believe the mix is lean and it will wrongly make the mix richer to compensate. A big or close enough leak can cause the sensor response to slow or even appear "stuck" at lean.

NewEdgeStang00

Cliffy you never disappoint me. Thanks for all your insight! Yes there is a substantial exhaust leak at the passenger side header to midpipe connection before the o2 sensors

cliffyk

That would do it...

NewEdgeStang00

I do have the option to turn off the rear o2 sensors. Would that help at all?

cliffyk

Not a bit--you need to fix the exhaust leak...

NewEdgeStang00

Here's the issue with the leak, the header has a little gap where it meets the midpipe. The drivers side came with a flared adapter, a cylinder sleeve, which helped cover that gap. However there isn't one for the passenger side. Any ideas on how to deal with this? I contacted American muscle, but they just sell the kits so I will have to contact MAC.

cliffyk

The passenger side is a flat flange connection that needs a gasket, unlike the ball and socket connection of the driver's side that does not.



Some aftermarket mid-pipes are not made well and need two gaskets to seal up the flanges--the engine will not run properly until this leak is fixed.

$6 to $8 at any FLAPS (Autozone $6.99)...

NewEdgeStang00

Thanks man that's exactly what I needed to know. Right now I'm getting this sound, is this the exhaust leak or something else? I have not heard this sound before except for when I had my 4.10s first installed and tuned. After the tune it produced this sound so I returned to stock, and retuned and it went away. But now it's there tune or not.