Basically the car is an 04 auto with rebuild done at rotary resurrection guy is knowledge about the 8s and has helped tremendously but I’ve not been able to solve the issue of stutter/backfire at higher rpms 4,500+ with throttle held down to redline has aftermarket coils installed 10,000 miles ago auto trans replaced with a lower mileage one not brand new and I’ve recently replaced oil cooler lines in their entirety problem occurred before the oil cooler lines.


Replaced trans and coils at mechanics recommendation I’ve done all the work myself besides the rebuild of the engine. No CEL I’m fairly new to the 8s but know enough to knock out some basic car issues also checked for vacuum leak no signs of one but is there a common spot to find one as well as possible clogged cat? Opinions?

 

I know my engine is on its way out, but I have similar issues.... my bet is the catalytic converter. I would check that before any other guess work. How’s your fuel mileage? I want to drop my cat early next week but if you get to your first I would love to hear what you find.....

 

It definitely sounds like the cat. Have a look in there.

 

Thanks guys I really appreciate it I’ll do some exhaust work and get back to you all.

ps. Gas mileage is awful just thought it was the norm for these cars from what I hear

 

You are right, it is the norm. You get about 12- 15 MPG city, 20+ highway.

 

Depends a bit how you drive, but 15 MPG is the absolute worst I've ever gotten. Much below that seems like cause for concern. Typically 18-22 mixed cycle.

 

Definitely how I drive haha! Car is in great shape. Good compression too.

 

I get 14 MPG in 90+% city driving and lots of full throttle.

I'd say city mileage is too variable to be useful. Highway should net you 20+ MPG consistently, though.

 

You can't drive one of these cars and not push it down at least once lol it's irresistible. It was so hard for me to break-in this engine (oh my god I'm glad it's done). Honestly I have never really kept track of the gas mileage. When it needs gas I put it in hahaha

 

Jhook123....any update???? Just to let you know I dropped my pipe and sure enough cat was in pieces..... installed a magnaflow cat and resonator for ~$150. Works wonders and car is back to pulling like it was new....

Cant pass emissions in NY with catless system.....so i only had a few options...

 

The aftermarket cat you got wont last very long so keep an eye on it as your problems return. Glad it worked for you though.