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Exhaust "thump" sound driving me crazy!!!

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Old 10-22-14, 07:28 AM   #1
MikesISF
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Question Exhaust "thump" sound driving me crazy!!!

Hello fellow F lovers!

If anyone can recall, I was having a sound from my exhaust. Basically when the car is rolling along around 25 MPH or so, and my foot is not on the gas, as soon as I gently touch the gas pedal, I get a soft "thump" sound. This basically tends to happen in 5th or 6th gear only.

The previous owner had done a muffler delete on the stock exhaust so I figured there was some sort of back pressure issue because of this.

Finally out of frustration, I sprung for a new Borla Catback exhaust system, hoping to eliminate this issue. While the thump sound is slightly less, it still happens!!!!

I was so hoping that the $1000 system and $150 install would finally solve the problem, but alas, it is still with me.

Can anyone please help me figure out this problem? If you need any more info, please post a response to this thread and I will respond as best as I can. Thanks in advance!
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Old 10-22-14, 09:34 AM   #2
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put your car on a lift, if it is your exhaust banging off something it should be too hard to find
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Old 10-22-14, 02:26 PM   #3
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you sure it's a "thump" and not a dull "pop?" it could be the unburnt fuel in the exhaust system that's 'popping.' even when before i deleted the middle borla resonator, the system would backfire/pop on deceleration, usually in 3rd gear in manual mode. i can make the dull 'pop' sound if i gently tap the gas from 3rd gear and up.
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Old 10-22-14, 02:51 PM   #4
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Quote:
Originally Posted by cremaster View Post
you sure it's a "thump" and not a dull "pop?" it could be the unburnt fuel in the exhaust system that's 'popping.' even when before i deleted the middle borla resonator, the system would backfire/pop on deceleration, usually in 3rd gear in manual mode. i can make the dull 'pop' sound if i gently tap the gas from 3rd gear and up.
Yes I think the pop sound could also describe it. It was doing it before, and after the borla install. So if that is the case, what can I do to fix it??
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Old 10-22-14, 05:22 PM   #5
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If you want to know if its the exhaust hitting up against something, you can put the car on a lift and shake the exhaust with your hands and see if it touches anywhere when its being moved. There isn't much space in some spots down there so if its not adjusted right it could tap against something under the car. Usually, it will occur when going over a dip or something. Mine makes a little pop sound when when I'm cruising and I give it some gas and then quickly take my foot off the pedal, its like a little backfire.
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Old 10-22-14, 05:43 PM   #6
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I have the pop, I love it. Especially with my muffler delete. I tap the pedal just to hear it
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Old 10-22-14, 06:47 PM   #7
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My JoeZ makes the "pop" too doesn't bother me.
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Old 10-22-14, 07:19 PM   #8
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its just unburned fuel. the pop sound is also called "backfire"
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Old 10-23-14, 05:08 AM   #9
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deng you are sure having some problems with your F. Are you sure it wasn't totaled or something like that in its past?

Any thoughts on selling it and buying another non modified F?
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Old 10-23-14, 07:02 AM   #10
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I have the same "pop" sound on the oem exhaust that has secondary cat delete. Is it normal sound on the ISF ?
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Old 10-23-14, 07:13 AM   #11
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I've had 2 ISFs.
My first was left bone stock and never made the "pop".
My second has a custom exhaust and makes the same "pop" sound when I barely touch the gas after having come off the gas. The custom exhaust only has one set of cats. Appears to be a standard issue with any aftermarket exhaust modification, but I'll check with one of my best friends who also has a modded F and see if he has the same issue.
I don't particularly care for the sound, but if it's not hurting anything, I can live with it.
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Old 10-23-14, 08:57 AM   #12
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Quote:
Originally Posted by MikesISF View Post
Yes I think the pop sound could also describe it. It was doing it before, and after the borla install. So if that is the case, what can I do to fix it??
fix it?? there's nothing wrong w/ it, it's normal w/ aftermarket exhausts or apparently, any modification to the oem. if you want to get rid of it, switch to full OEM system. i personally love any and all pops the exhaust makes.
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Old 10-23-14, 06:03 PM   #13
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I don't have any pop and I'm on ppe and borla.
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Old Yesterday, 01:28 AM   #14
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I don't think we are talking about the same sound. This sound doesn't seem to be backfire or a pop. It is like a thump that you feel in the floor of the car. Almost like as if a valve flap was closing or something.

It isn't a major sound, and since I went from the OEM exhaust with muffler delete, to the Borla, the sound is less but still exists.

Thanks for the reply, keep me updated for the poster who mention he would check with his friend!
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Old Yesterday, 08:33 AM   #15
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It's likely a similar issue that I'm experiencing. Part of the exhaust is resting against the bottom of the car. When you hit a bump, it stretches the exhaust hanger slightly and the thud you're hearing is when it contracts and the exhaust hits the car again. I'm heading back to the shop today to attempt to resolve this issue.

http://www.clublexus.com/forums/is-f...axle-back.html
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Old Yesterday, 08:33 AM
 
 
 
 
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