Popping exhaust

Engines, Transmissions, running gear, etc.

Moderator: Larry Jowdy

Popping exhaust

Postby sjgharib » Tue May 16, 2017 10:51 am

What makes my exhaust pop on throttle lift off while still in gear?

I have a 2.5L Subaru with fuel injection. Exhaust is custom 4-2-1 with basically glass pack mufflers (it's loud!).

I know some boy-racers like the noise, but should it be a concern? I basically sound like an F1 car under braking.

Thanks!
Simon
User avatar
sjgharib
$$Donating Member$$
$$Donating Member$$
 
Posts: 378
Joined: Mon Jul 13, 2009 6:56 am
Location: Killingworth, CT

Re: Popping exhaust

Postby Larry Jowdy » Tue May 16, 2017 12:09 pm

I could be an exhaust leak. They're prone to leaking at the manifold. Usually easy to tell as there will be carbon deposits on the cylinder head. If the exhaust system is sectioned together and clamped, look for traces of carbon on the inner pipe. Another condition is you're going extremely lean when you lift your foot off the gas pedal.
Larry Jowdy
Site Administrator
User avatar
Larry Jowdy
Site Admin/Owner
Site Admin/Owner
 
Posts: 8413
Joined: Sat Jun 14, 2003 11:00 pm
Location: Ontario, California USA

Re: Popping exhaust

Postby EEricson » Wed May 17, 2017 6:32 pm

My Subie burbles just a little but I put it down to the short pipes. I like Larry's diagnosis; unless you're running Webers or something there's not much on a Suby that can go wrong and give you this symptom.
EEricson
$$Donating Member$$
$$Donating Member$$
 
Posts: 233
Joined: Wed Apr 26, 2017 5:22 am

Re: Popping exhaust

Postby sjgharib » Mon Sep 11, 2017 12:33 pm

Very lean? Interesting to understand that phenomenon. I've done some more research and that sounds like where to start.

I'm running a megasquirt ECU, and I know I've got it cutting the fuel on over-run... I'll try turning that off and see what happens. I'm also betting my fuel map is too low at low vacuum, which apparently (according to the megasquirt community) is a common thing to get when you let the computer tune itself...

It's a one piece welded exhaust, no visible leaks (at least that I can see)...

Thanks,
Simon
User avatar
sjgharib
$$Donating Member$$
$$Donating Member$$
 
Posts: 378
Joined: Mon Jul 13, 2009 6:56 am
Location: Killingworth, CT

Re: Popping exhaust

Postby Larry Jowdy » Tue Sep 12, 2017 7:46 am

If the exhaust is truly a one piece then check your exhaust manifold gaskets. They're notorious for leaking with aftermarket exhaust systems.
Larry Jowdy
Site Administrator
User avatar
Larry Jowdy
Site Admin/Owner
Site Admin/Owner
 
Posts: 8413
Joined: Sat Jun 14, 2003 11:00 pm
Location: Ontario, California USA

Re: Popping exhaust

Postby sjgharib » Fri Sep 29, 2017 5:45 am

I'm going to replace the whole thing with a new stainless one this winter, so I'll check the gaskets... I actually built the entire exhaust myself from mandrel bends and muffler components (http://coneeng.com). I was poor at the time (spent all my $$ on other parts) and thus I went with mild steel tube instead of stainless. I don't like the rusty look, so exhaust 2.0 (100% stainless) will be a project in the coming weeks!

Has anyone had any experience with the "auger" style muffler inserts? I was going to try them instead of perforated tubes and steel wool.
User avatar
sjgharib
$$Donating Member$$
$$Donating Member$$
 
Posts: 378
Joined: Mon Jul 13, 2009 6:56 am
Location: Killingworth, CT


Return to Tech Engines/Mechanical

Who is online

Users browsing this forum: No registered users and 20 guests