I put my Stillen Y-Pipe on my 4th gen. The car is acting funny. Before the Y-Pipe, when I let off the gas (in gear, high rpm), the car slowed down immediately without braking. From what I understand about electronic fuel injection, this is because the ECU senses that I am running at a relatively high RPM and no throttle, so it runs the fuel mixture all the full lean, thereby pumping only air through the engine to conserve gas and slow the car down. My car is not slowing down well while it's in gear. It seems to keep pushing more when I give it no throttle. Could this in any way be due to the Y-pipe? Are my fuel injectors not going full lean when I give no throttle in gear? Or is it just a side effect of a lower backpressure exhaust system?

PS: Sorry for the cross-post.

 

Perhaps your engine is failing to give normal engine braking because...
- the throttle cables are misadjusted (there should be a bit of slack)
- the throttle blade is obstructed (dirt buildup)
- the Throttle Position Sensor is misadjusted or defective (the Engine Control Module doesn't know you have lifted your foot off the accelerator)

 

Thanks for the reply. I am really not enjoying this side effect of the y-pipe, especially if my gas mileage starts to go down. I dont think the throttle body was messed with during the install. I will check the slack in the throttle cables in the morning. Do the O2 sensors have anything to do with proper engine braking? Maybe they are not giving the ECU correct readings? I suppose keeping track of gas mileage will be the true test of what's going on here.

 

I think PCV valve also helps controls the fuel mixture (i read it somewhere but not sure)

Any opinion Mr. Martin?

 

No.