4.0 possible muffler issues?

[88mancheman]

Hey all after weeks and weeks of hard work the Comanche is almost ready for summer EXECPT... the ole 4.0 seems to be knocking somehow... she had a bad flex plate knock that I addressed last weekend but after I was all finished up I took her on a test drive she was perfect for the first 20 minutes or so but as soon as I came to a stop light and idled for a few minutes I noticed there was a slight knock, I pulled over and inspected and it defiantly sounded like the engine had a slight knock at idle but nothing past idle.. so I let her cool off and drove her slowly home listening for odd sounds, nothing happend on the drive home but as soon as I pulled her into the garage I noticed she was spitting a tiny bit of oil out the tail pipe onto the wall..... I shut her down and have been pondering what could have caused this, as the only 3 things I’ve done to the engine in the past 6 months have been a new radiator, flex plate and muffler.... then I got to thinking...the muffler I welded up was an old flow master off a friends 5.0 v8 mustang it was a the same diameter as the Jeep and from a v8 so I figured it would have a larger flow and work just fine, but is it possible that this muffler is causing too much back pressure and harming my engine? Or is this starting to sound like a rebuild...?

[Pete M]

I don't think it's the muffler.  Cats go bad all the time and cause way more backpressure but that doesn't cause knocking. 

 

I would revisit the flex plate, just to be sure.  

[88mancheman]

I don't think it's the muffler.  Cats go bad all the time and cause way more backpressure but that doesn't cause knocking. 

 

I would revisit the flex plate, just to be sure.  

 

I will defiantly double check everything on the transmission and checkout the flexplate again but I’m slightly concerned about the black oil looking stuff that was coming out of the tail pipe I’ll have to update in better detail this weekend when I get back around to checking her out :)