Alright guys. I got lots of good info from the last post I submitted and decided to go with the FlowMaster 40 series. But, I now have a concern. I got the whole exhaust system install Monday and my concern is that when I rev the engine while the transmittion is in park I can hear loud popping noises it almost sounds as if the engine is back firing. This only happens at high RPM. I never noticed this when I had the stock exhaust. Does anyone have a clue as to what might be causing it?

 

Could be an air leak upstream of the cat... actually sucking it in and popping when it hits the cat(s),

Did they touch anything upstream of the muffler clamps?

 

CentralCoaster,

It was exhaust with cat-back installed.

 

I don't think I got the idea.

Correct me if I am wrong, please.
You put a lower restriction exhaust on.
Didn't let the PCM 'learn' it (100 miles or so, at least that is what I keep getting told by the Ford guys).
And you are revving it to high RPM in park?
How high is High?
Exhaust popping is usually either the timing is too retarded, or your mix is too rich. Over scavaging at high RPM?

High RPM with no load (3000+) is not really a great idea.

Have you done a visual, looked for sensers they unhooked or cut? O2 sensers like to come off of these in exhaust work.
Any codes?
Chris

 

The popping noise is probably just excess back-pressure. It has to go somewhere, so it just gets forced out the tailpipe. The factory exhaust is "tuned" to factory setup. If you introduce less restriction (by adding a larger, less-restrictive cat-back) you will get more backpressure than is required to remove the exhaust gaes. The computer has to "re-learn" it's air/fuel settings before it gets back to normal. I'd be willing to bet you are running richer than before, the evidence of this will be in the form of black residue in and around your tailpipe. Do several normal drive cycles and let the computer relearn the new set-up and then see what happens.

I'm with Chris here, revving the engine for the sake of hearing the new exhaust is not a real good idea to begin with. I know you want all your friends and neighbors to hear it, so just do some drive-by's or take them for a ride.

I had an SVT Focus and I replaced the cat with an off-road pipe (so it was a 4-2-1 longtube header, then straight pipe into a muffler and out the back) and it would pop like crazy when it was cold. This usually only happened when I was decelerating and removed the load on the engine by pressing the clutch. Once it warmed up it didn't do it as often. I have actually seen people with that exact setup blow flames out of their tailpipe... can you say excessively rich?

I wouldn't worry too much about it, it's not really hurting anything. Just let the computer do it's thing and then try to refrain from starting a cold engine and revving the crap out of it... all cool as it sounds!

 

ChrisAdams,

The truck only has about 25 miles with the new exhaust. I didn't think about the PCM having to learn it. I'll drive it around as usual and see if it will take care of the problem after puting some miles on it. And yes, high rev was actually 3000+. I'll just have to refrain from revving the engine to show-off.

Onespeed,

I haven't noticed any residue on the tail pipe yet since i haven't driven it around enough but i'll keep my eyes open. I also talked to a friend of mine a few minutes ago and he also mentioned the same thing that you and ChrisAdams said about this PCM learning thing. i'll give it some time and see what happens.

Thanks guys all you time and help