For a few months I've had a Stillen Y-pipe on my car that didn't fit exactly right and was leaking, apparently causing other problems. Recently I replaced it with a Cattman Y-pipe which fixed the leak and sounds much better, but I still get knocking on moderate acceleration. Also, my fuel economy hasn't gone back up to where it was before the Y-pipe, and even at full throttle it seems to not pull like it should. I was wondering if these issues are caused by faulty ignition coils or something else? My Max is a mid '99 build with Cali. emissions. Could it be that I damaged an O2 sensor during the install? It just seems that everything was fine until I removed the stock Y-pipe.

Anybody else have similar experiences?

 

when i first installed my y-pipe, it was leaking only cuz i didn't align the top gasket properly and it got pinched. after fixing that, i didn't have any problems with my y-pipe whatsoever.

 

faulty coils could cause lack of power or reduction in gas mileage....

 

i just put on my cattman about a month and had some leaking, so i just took it back down, used new gaskets and used some patience and now everything sounds good. the knocking or banging could be the y pipe hit against the exhaust bracket. its black and has 8 bolts. im planning on getting different bolts, but for now its just on and the banging has gone away. i kept the negative post over night and my gas mileage is around the same if not up a little bit.

 

It's definitely engine knock (ping) and not the exhaust hitting the vehicle crossmemeber. I fixed that by using two washers at each bolt to offset that bracket from the body. Now it only bangs on hard launches in first gear. Like you, I need to get longer bolts before I put any more washers under there.