Hello Everyone! I am a new member. Looks like a great forum!

I wanted to see if anyone had any ideas on my exhaust dilemma. I just installed a Flowmaster “Super 40” muffler and turned a 3” tail pipe out in front of the rear tire. It sounds awesome, but I think it might be too free flowing for the computer.

I did loose some low-end snap and gained a noticeable amount of power on the high-end (it pulls stronger and longer 4000-5700rpm), but the strange thing is that it now stumbles making the 1st to 2nd gear shift. It actually cuts-out right at the peak, and then stumbles a little bit as it recovers in 2nd gear. Also, I can’t rev the engine past 4200rpm when it is not loaded (park/neutral), it actually cuts off like fuel or spark is being shut down temporarily.

I am guessing that the stock computer setup cannot deal with the drastic reduction in backpressure. When I first took the exhaust off, I took the truck on a test drive with just the straight pipe coming off the cats and it could not accelerate without stumbling and cutting out at high rpm, so the super 40 and tail pipe brought it back in a bit, but not completely.

I am hoping that this can be fixed with a chip/programmer, or some other mod. I don’t want to give up my new sound.

Any thoughts?

 

I forgot to mention that the truck only has 1800 miles. I am not sure it a break in period programming would make a difference, or if there is such a thing as break in programming in the computer. I have read some posts that mentioned it.

 

What engine do you have? I'm pretty sure the 4200 RPM issue while in park is standard. Mine does the same thing. Some say the Hemi engine is touchy when it comes to backpressure, especially if you don't provide enough incoming air to the engine.

I do know that FlowMaster indicated at one time the only muffler they recommended for the Hemi was their Hemi-specific 50. However, others have used other FlowMaster mufflers on their Hemis without issue.

I would disconnect the negative cable to the battery for about 30 minutes or so, then reconnect it. That should reset the computer to its original state. That might help, but I would hold off to see if you get some more response to confirm. Good luck.

 

mazz,

Thanks for the tip. I forgot that a re-set might make a difference. I will give it a try and post back.

The engine is 5.7 hemi.

I thought that the stock air intake/filter was a pretty good piece as is, so I was thinking that intake air volume would not be the problem. I don't feel like spending 300.00 to test it. Maybe I will make one test drive without the air box and see if the intake airflow is the problem.

It really does act like the fuel or possibly the spark is cut off. Strange.

Oops. I did not realize that flowmaster only recommended their hemi muffler. I will keep my super 40 and look for a work around. I just hope I am not damaging anything.

Thanks.

 

The Rev Limiter in Park-Neutral is normal
I'm just brainstorming here but you need a friend at the dealership that knows what he's doing
If the battery disconnect does not work...... it is possible your knock sensors are "Hearing" your exhaust and retarding your timing
the cats alone should supply enough "backpressure" for proper scaveging (sp?) effect

 

Don't have a friend at the dealer yet, but smart thinking on the knock/retard.

I just got back from a test run. It is better, but not fixed entirely. I think I can deal with it now. Thanks for confirming the rev limiter thing. That one scared me.

I made two changes (I know, I should have made one at a time). I disconnected the negative batt. cable and while I was killing time, I noticed that the hose clamp on my intake tube at the throttle body side was seriously askew. It was only clamping the top and making a gap in the bottom. My hemi has been sucking unfiltered air right off the manifold since day one!

Luckily, I have not been in dust/dirt and only 1800 miles on clock.

The situation did improve, but is still acts a little funny.

Thanks for all the tips.

 

Did you remove the Catalyatic Converters when you replaced the stock mufflers?

 

No. I still have the cats.

I put the Super 40 on the stock pipe right where the stock muffler clamps on. Then just a 3" tail pipe turned out in front of the wheel-no resonator.

It sounds very tough/great. Rumble in the cab is not even half as bad as I expected. I am very happy with the sound and the extra power on the top end.

There is still a slight stumble going from 1st to 2nd at full throttle. Maybe I am just getting into the rev limiter as it starts to shift. It did not do this at all befor the exhaust change.

I am still trippin about the test drive I took with no muffler/pipe, just cats. It would barely accelerate and stumble like crazy. It was a mess. Sounded bad too. I guess whatever was causing that, I still have a tiny bit of it left, but not enough to make me change my exhaust back!

 

I got the flowmaster 50 series muffler with a 3" flowtech cutout. You wanted to do a cutout AFTER the exhaust? I wouldn't see the sense in that, its not that much piping after it, anyhow, I put mine before the muffler. check it out

 

thats crazy, driving w/ just cats.
people these days , sheesh.