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The problem your describing sounds like an egr related problem. Alot of people have it, do a search under stumble and you'll see how many of us have problems with it. Just guessing but if you haven't replaced your dpfe sensor at least once thats probally part of the problem.
 

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Exhaust leaks,if large enough,will cause a loss of power. This would have to be a pretty large leak like a loose header,cat or muffler,broken weld,etc.Sometimes a leak would cause backfire under deceleration.For sure,a leak would smell and you would smell it while you are driving.You might also hear a sort of hissing sound.
The stock Focus exhaust system is heavy, strong and welded together.
It seems that aftermarket headers are more delicate than the heavy (but strong)stock exhaust manifold. A lot of them crack at the welds. This is due to most of them being made of stainless steel.
I recently chased down some exhaust leaks that came from the slip joints on my cat back system.Even these small leaks made me loaded when I drove around.I tried to tighten the standard muffler clamps, but the would'nt seal.I found some preformed band clamps made by Walker that solved the problem.Most of the aftermarket cat backs have slip joints that sure could benefit from these band clamps.I know that some have flanged joints, but most don't.
So I would check to see if if your JBA is tight. These things should be checked and re- torqued.Check the collector flange for tightness and both cat gaskets.From that point,it's just the flex pipe joints,gasket and the slip (or flanged) joints from the flex pipe back.
Hope you find the leak.
 

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I need some help! What is typical of an exhaust leak in terms of the drive performance.

I installed a JBA Gen 3 and didn't notice any issues with performance at first. Even wrapped on it at the dyno.

Recently I've developed a hiccup under light/moderate load under 3000 rpms. In second gear it happens almost religiously under gradual accleration at 2400 rpms. A little higher rpm in 3rd gear. If I'm in too high a gear and push the pedal half way (which is what I mean by moderate) I get the brief studders.

Now I've experience spark plug and wire problems in the past and driven on 3 cylinders and this is no where close to as drastic a difference. Plus WOT it rarely stutters at all, and never in 3rd or 4th when accelerating hard from launch.

It's weird that I only get it at low RPM and low acceleration. Doesn't seem to me that it's a fried cat and I have no CEL. I'm also running two FS wires and 2 stockers while I wait from my defunct FS wires to be exchanged. Any thoughts?

Thanks!
 

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Well, exhaust leak means the loss of exhaust vacuum (thus scavenging) and generally has two easily identifiable symptoms:

1) Exhaust sound changes (mostly increases), change amount depending on the shape, place and size of the leak...If the leak is big enough, sound increases noticably as the leak causes the mufflers to be by-passed, and brings the gas exit point (sound source) closer to the driver...

2) Torque loss, as the internal exhaus pressure (vacuum) is breached and scavenging effect is lost, amount depending on the size&place of the leak...

These are the basic rules. Hiccups seemed a little strange to me...I would rather go for an ECU/sensor problem in your case as it developped gradually (yeah, I know this is also the way leaks work)

Anyhow, there is a easy way as long as you have a canal (that's what we call it in Turkish - a pit you can enter and drive the car over so that you can work on underside) you can use. Pull over the canal, go in, start the car and temporarily clog the exhaust exit with a cloth. That way you can easily hear any leaks in the system...

[ 02-14-2003, 11:55 AM: Message edited by: Cem Aygun ]
 
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