Changes in tone of exhaust while stopped. - Ford Mustang Forum
 
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post #1 of 7 (permalink) Old 11-18-2010 Thread Starter
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Changes in tone of exhaust while stopped.

Guys,
First off, this is an awesome site. Lots of questions and answers being passed around. This is great. Glad to be a part of this.
My question is!
I have the Roush exhaust on my 2011 5.0. And while stopped at lights, etc, you can actually hear the exhaust tone change pitch and tone. Sounds like the cam timing is changing. Has anybody else noticed this. Is very noticable with the louder exhausts. I would assume ignition timing may be changing, but would the cam timing actually change at idle?
Thanks in advance, Dave


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post #2 of 7 (permalink) Old 11-18-2010
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It's the A/C compressor turning on and off. Mine does the same thing.

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post #3 of 7 (permalink) Old 11-18-2010
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It is the air conditioning compressor cycling on and off. It effects the idle.
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post #4 of 7 (permalink) Old 11-18-2010 Thread Starter
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Guys,
All climate controls are off. I am in the HVAC trade and it is not the ac compressor cycling. The Exhaust will get loud and then very soft. It is an ignition timing deal or cam valve timing change.
I have been around hot cars and rebuilt several small block Chevys over the years, played with all different compressions, cams, etc, so hearing the exhaust note change is something very new to this Old School hot rodder.
I am used to hearing a constant exhaust or even the lope of a big cam as idle.
An ideas?

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post #5 of 7 (permalink) Old 11-18-2010
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yeah, the idle on the stock and tuned cars seems to surge abit. Sometimes worse than others, its the pcm configuring the a/f ration when the car is at idle. I believe one posted that if you have a bad idle surge problem, which will make your exhaust note go up and down as we all know, you disconnect the battery cable for a while then hook it back up and then cold start the car let it idle for 5 minutes then drive about half an hour and the problem will be fixed. Or atleast the pcm will get a closer reading on the a/f fuel. While i dont know for sure though, but my car has settled down abit. After breakin, the cars idle surged from 5-1000rpm sometimes which is alot. It also seems to help when i run 93 octane. unless you are having serious issues which involves taking it back to the dealership, I'd let it go.

2011 Mustang GT premium, Black on Black, 6 speed manual,Brembo pckg,HID's,3.73's, appearance package, Security,Comfort,Roush Axelback, Q Ball shifer, Bama Race Tuned, UMI Brackets and LCA's, K&N drop in filter and more to come...
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post #6 of 7 (permalink) Old 11-19-2010 Thread Starter
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Thanks. I just found a thread talking about the idle surging. The site is great for info about this car..

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post #7 of 7 (permalink) Old 11-19-2010
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Quote:
Originally Posted by jcm2011gt View Post
yeah, the idle on the stock and tuned cars seems to surge abit. Sometimes worse than others, its the pcm configuring the a/f ration when the car is at idle. I believe one posted that if you have a bad idle surge problem, which will make your exhaust note go up and down as we all know, you disconnect the battery cable for a while then hook it back up and then cold start the car let it idle for 5 minutes then drive about half an hour and the problem will be fixed. Or atleast the pcm will get a closer reading on the a/f fuel. While i dont know for sure though, but my car has settled down abit. After breakin, the cars idle surged from 5-1000rpm sometimes which is alot. It also seems to help when i run 93 octane. unless you are having serious issues which involves taking it back to the dealership, I'd let it go.


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Mine did the RPM surge to. 500-1000RPM as well. However mine at 500RPM would sometimes almost stall and then surge back up to 1000RPM. And on rare occasions it would stall. It was driving me nuts. I have a post somewhere on here about it I tried 93 octane to and did not make a difference so there was a problem. Dealer changed a bunch of parts. Last one the throttle body. Fixed issue Would not say this engine idles perfectly but 100% better then with the surge.
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