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Old 10-28-2012, 12:13 PM   #1
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ZX5, Cut the muffler off, now having issues

My son removed his muffler about 3 months ago wanting his car to sound "loud". The car smells like exhaust now inside and it's gradually running worse and worse. My thoughts are he has done damage by shortening the muffler but he says that will cause NO problems. His gas mileage has also gone to hell in a hand basket since this modification. Can anyone shed any light on this? There's a reason the muffler was made the length it was. His check engine light has come on a few times with his O2 sensor being the code. I think this all goes back to this missing muffler.

Also, yesterday, the car is now stuck in gear (manual) and he can't figure that out either.

Thanks to all responders,

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Old 10-28-2012, 12:36 PM   #2
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Removing the muffler alone should not cause any problems. Usually the fuel economy goes out the window because you like to hear the sou d or make the thunder so your heaver on the throttle. That's where you have to worry about doing performance mods for MPG gains. Exhaust and intake systems can provide an increase in MPG but usually it goes out the window because you like the sou d of the air intake at WOT or the sound of the exhaust when you down shift and let off the throttle quickly.

By muffler your son removed the large muffler in the middle of the car? That should be replaced with something to remove the exhaust fumes from under the car to exit from the rear of the vehicle. Some cheap flexible pipe and exhaust claps can fix that. Mufflers are chosen purely on consumer expectations on what that type of car should sound like. People who by the focus generally want it to be a quiet car so it gets muffler that will balance that out while keeping power and fuel economy also in what the consumer wants. That's why a focus on a stock exhaust you might not know its on. And on a 5.0L Mustang GT you feel the rumble.

Stuck in gear... he can't shift it out from 2nd to 3rd? It shifts out of gear but does not go back into gear?
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Old 10-28-2012, 12:38 PM   #3
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If he removed the rear resonator (called the lunch box, because of it looks) it will cause no harm so you can give him a break. As long as the cat and header is still intact then the oxygen sensor isn't affected, so it nay just be faulty like any other o2 sensor that's old. If he removed the full cat back exhaust or flex back than that would explain poor mileage and gas smell.

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Old 10-28-2012, 07:45 PM   #4
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Cutting off the muffler by itself won't cause any issues. Now when he cut it off, did he not have another pipe welded in it's place to vent the gases out from under the car or did he just leave the pipe cut under the car? That's about the only explanation I can think of as to why you have fumes getting into the cabin of the vehicle. And as for your MPG issue, that's something completely different and should not be affected by just cutting off the muffler.
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Old 10-28-2012, 08:00 PM   #5
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Give your son some slack you sound just like my dad lol

Cutting the muffler off will do nothing but make it louder and if you don't replace the muffler with some length of pipe to exit out from under the car then you can and will get exhaust fumes inside which as you know is bad. Fix it before it gets too cold outside. Carbon Monoxide fumes are BAD for you and you don't know it till its too late. That's why people shove a garden hose in the muffler and route to the window when they want to kill them selves.

The bad gas mileage if from the bad O2 sensor which has nothing to do with the muffler being cut off. It's just a coincidence that this happened at the same time. I highly recommend getting a new from Rockauto.com they have great prices and beat most prices.
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Old 10-28-2012, 08:57 PM   #6
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To add to this some. If he did replace the section he cut out check the flex pipe to be sure it hasn't rusted to the point where it is no longer connected. I had that happen to me and man did the car stink till I fixed it.
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Old 10-28-2012, 09:49 PM   #7
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Or do a nice job with a walker pipe that will fit ! Here's my resonator delete...if he removed the mufler, he will need to put a pipe too.

My exhaust end 2'' walker pipe and a 3'' SS tip
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Old 10-29-2012, 05:19 AM   #8
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Thanks to all responses. ZetecDon, you hit the nail right on the head, he did NOT have any other pipe welded in it's place. I told him that was not safe from the start. I will insist that he do something with the fumes being as now he always has the windows up because our weather is cold.

FocusBlackZX5, that looks good but his does not look like that. I would be happy with your set up. : )

As far as the shifting issue. I researched on this wonderful site yesterday and it was the shifter cable had separated. We got that back together and restrained them with a few thick cable ties. Voila! The shifter now works just fine.

Thanks again everyone. I really appreciate all of the feedback. I'm not trying to be a hard nosed parent, I just don't want to have my son end up with headaches, brain fog, or even worse..death due to a repairable issue. I just want him to be safe in his car.

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Old 10-29-2012, 05:25 AM   #9
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Doesn't the engine require the back pressure from the muffler to run properly. I've thought that the exhaust valves will get burnt w/o some type of back pressure. Is this true or not?
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Old 10-29-2012, 05:40 AM   #10
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absolutely understand... we've all done the stupid things.

so which one did he cut off? just the back one?

if he wants any incentive to fix this, its not safety legal, he can receive a ticket and like you said with the windows up it will leak inside.

As far as mileage goes. Its either his right foot or it may be time for a tune up. I'd caution against just stating the 02 sensor is the problem. though it wouldn't hurt to replace, they are about $67.

just check the plugs and replace the fuel filter first if necessary. check the air filter... you know, that kinda stuff.

as far as the rest of the exhaust, the clamp and flex tubing works. a local shop could do it pretty cheap if they can weld. I'd probably charge about $30 to bend and weld a piece that makes it out the back. be aware that I once had a muffler shop want $90 to fix a flange gasket and refused to weld it up for me after I asked. it all depends on who you go to.

edit: on back pressure... that depends on how much he cut off. if it was not much further after the flex then there could be a problem. in this case that will not be an issue.
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