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Discussion Starter #1
This is a long shot, but here goes. This car is a garage queen that is rarely driven. I drove it to work this morning and noticed under load, the exhaust has a cherry-bomb like sound with very little acceleration, but the gauge shows boost. I babied it home but took a short vid where you can hear the miss/hesitation and laziness to rev. It idles smooth, no CELs. Checking for vacuum leaks now...any insight would be awesome cuz I’m lost. Car is stock except for the VMP Stage 2 from a year ago (TB, tune, JLT). It’s ran flawlessly...until today. Turned 19k miles today.
 

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2014 Shelby GT500 2013 F150 SVT Raptor
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First thought. How old is the gas in it?
 

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Discussion Starter #4
Reading the cats might be toast. Anyway to tell besides dropping the pipes?
 

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2011 Shelby GT500
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Reading the cats might be toast. Anyway to tell besides dropping the pipes?
Check for codes? I would think any modern car with post cat o2 sensor would trip a code for less optimal functioning catalyst
 

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i missed that you scanned it, then again cels or codes for emissions are not triggered on every drive mine sets a cel for cats that is no longer there, but it takes a long trip to set it
 

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Check to make sure your intercooler pump is working. When you first fire up the car, is the power good? If your pump isn’t working, power will be good until the car gets warm/hot and then it will have very little power.
 

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Discussion Starter #9
Check to make sure your intercooler pump is working. When you first fire up the car, is the power good? If your pump isn’t working, power will be good until the car gets warm/hot and then it will have very little power.
Pump is good, Goose. I have good movement in the tank since jumping the harness a while back. The exhaust sound is deep, choppy and sluggish, not a smooth powerful rev like usual.
 

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Pump is good, Goose. I have good movement in the tank since jumping the harness a while back. The exhaust sound is deep, choppy and sluggish, not a smooth powerful rev like usual.
If your cats have melted/plugged, you should see a higher boost reading. Of course running like that is not good.
 

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2014 GT500 PP
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Drove mine over the weekend and it had a bog it seemed like when I would jump on the throttle. It ran decent but didn't have the rawness it used to. Finally realized I hadn't turned off the nanies.

Nanies off?

Tom
 

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Discussion Starter #12
Drove mine over the weekend and it had a bog it seemed like when I would jump on the throttle. It ran decent but didn't have the rawness it used to. Finally realized I hadn't turned off the nanies.

Nanies off?

Tom
Yep!
 

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Explain "cherry-bomb like sound". I don't know if you're describing a large misfire or a louder than normal exhaust note.
 

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Discussion Starter #14
Explain "cherry-bomb like sound". I don't know if you're describing a large misfire or a louder than normal exhaust note.
It has a throbbing/pulsating exhaust sound when under load and boost (only for a few seconds then I let off). Normal cruising sounds the same as usual...I have a small video from yesterday that I can send you...
 

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It has a throbbing/pulsating exhaust sound when under load and boost (only for a few seconds then I let off). Normal cruising sounds the same as usual...I have a small video from yesterday that I can send you...
Do your RPMs increase without a corresponding increase in MPH (toasted clutch)?
 

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Discussion Starter #16
Do your RPMs increase without a corresponding increase in MPH (toasted clutch)?
Nope, clutch is good. I won’t have time until Friday to drop the cats. It runs good at cruising speeds plus a solid idle, so unsure about vacuum leaks or coil/plugs. It seems only when I give more throttle and get into boost that the exhaust starts that shuttering sound and speed falls
 

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I had a very similar experience with my old 03 Mach 1. I thought it was bad gas because it would sit for long periods, but fresh gas didn't help it. Wasn't triggering any check engine codes either. Turned out to be ignition coil pack. The interesting thing is that engine used the same coil packs as the GT500. I never figured out which one it was, I ordered a set of 8 and replaced them all.

Another thought I had is maybe mice got into the exhaust and nested?
 

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Discussion Starter #18
I had a very similar experience with my old 03 Mach 1. I thought it was bad gas because it would sit for long periods, but fresh gas didn't help it. Wasn't triggering any check engine codes either. Turned out to be ignition coil pack. The interesting thing is that engine used the same coil packs as the GT500. I never figured out which one it was, I ordered a set of 8 and replaced them all.

Another thought I had is maybe mice got into the exhaust and nested?
I’d almost wish for a CEL to give a misfire cylinder...or some direction. Thx for your inputs
 

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I’d almost wish for a CEL to give a misfire cylinder...or some direction. Thx for your inputs
Yeah, that would make life easier for sure. I had the exact same thought when it happened to my Mach 1. I posted up on the Mach 1 forum and a member said he had the same problem and it ended up being an ignition coil pack. I took the chance, and it worked out.

I don't normally subscribe to swapping parts without testing them, so I'm not suggesting you do that either. I'm not entirely sure how you would test the coil packs? Maybe there's a specified resistance range?
 

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Without codes, it makes for difficult diagnosis. I'd pull the plugs and inspect them to see if anything looks out of the norm. If you suspect cats, you might have someone rev the engine up to 2-3,000 rpm and see if you notice any change in exhaust volume. The cross-over pipe might compensate.
 
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