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Thread: Jake Brake !?
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11-18-2009, 11:48 AM #1
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Icelandic Silver- 2000 SS / 71 Chevelle 454
Jake Brake !?
I'm just curious, I can't remember if my car did this when the stock exhaust was on the vehicle or not. I have a 00 SS M6 with pacesetter LT, ORY and a LM 2. When down shifting, after my foot is off the accelerator the vehicle slows normally, then makes this sound like a jake brake and begins to slow quite quickly. Is this a problem or an exhaust leak or something, the car doesn't make any ticking noises or have anything else moded on it except the exhaust. Does this happen on everyones cars?? Thanks.
VooDoo.
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11-18-2009, 12:01 PM #2
Suggestion: If you are particularly irritated by another member's posting habits and are constantly fighting the urge to flame them, you can click on that person's profile, and select "Add to ignore list." This will make that person's posts invisible to you.
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11-18-2009, 12:17 PM #3
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Icelandic Silver- 2000 SS / 71 Chevelle 454
Yeah, I got that part, thanks. The sound happens a few seconds after my foot comes completely off of the throttle, it may be nothing, just wondering if this is something that is unique to the LS1 or is it a byproduct of the exhaust setup?
VooDoo
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11-18-2009, 01:01 PM #4
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11-18-2009, 01:04 PM #5
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11-18-2009, 01:10 PM #6
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11-18-2009, 01:16 PM #7
Jake Brake and Exhaust brake are two completely different devices used.
Jake braked equipped engines cylinder heads have another exhuast valve which is activated by a solenoid usually when pedal is released/JB activated. Its opened near TDC to help release pressure and not pushing the piston back down. In turn, that slows the truck down.
Exhaust brake shuts off the exhaust after the exhaust manifold.
Neither of these is happening on your car, I can assure you
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11-18-2009, 01:17 PM #8
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11-18-2009, 01:19 PM #9
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11-18-2009, 01:23 PM #10
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11-18-2009, 08:48 PM #11
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- Aug 2005
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- New york
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SOM- 2002 SS
i know exactly what you're talking about. it did it when I had the gmmg. its just backpressure. totally normal.
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11-18-2009, 09:25 PM #12
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Icelandic Silver- 2000 SS / 71 Chevelle 454
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11-18-2009, 09:27 PM #13
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11-19-2009, 12:13 AM #14
Okay I'm going to explain this the best I can since post #2 was overly simplistic.. You can not hear "back pressure".. If you have a loud exhaust what you are hearing is the compression of the engine being used to slow the momentum+weight of the vehicle. Combustion is still taking place, however when you let off of the gas, no more fuel is being applied to the engine except what it takes for the engine to achieve idle.. As the rotating mass begins to slow, so do the frequency of explosions in the combustion process, hence the change in pitch/sound you are hearing. Same process happens to a "free" spinning engine but @ a much faster rate, due to the fact that alone, an engine has much less mass being applied to its compression as it begins to slow down.
An engine is nothing more than a big air compressor. A shop air compressor has its exhaust pluged with an air tank. The sound its compressor makes is air being breathed in and forced into the tank, you do not hear the air in the tank pushing back. So what do you think happens with an open exhaust pipe on an engine with your foot off the gas? Answer, nothing.. The air just escapes.. The explosions are not strong enough to create "quote" back pressure, so the air just escapes with the sound of a weak explosion in it.. Oh yeah it's normal don't sweat it..Last edited by Smittro; 11-19-2009 at 01:04 AM.
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11-19-2009, 01:00 AM #15
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11-19-2009, 01:00 AM #16
Oh and yes its normal! My car has done it since day 1
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11-19-2009, 01:01 AM #17
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11-19-2009, 02:20 AM #18
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Black- 2000 WS6 6spd Hooker LT
A few people who posted are close to right, but the exact thing that is happening is given by the clue he describes that I highlighted.
What really happens after you let your foot all the way off the throttle, after a couple seconds, is that the PCM shuts off the fuel almost completely. The injector pulse goes to abour .5 ms, when idling the pulse is around 2 ms That's the different sound you hear. It also slows the car quicker since there is no fuel being supplied. When you first let off the gas, in gear, the PCM strategy still allows the idle fuel injector pulse, then it changes to the .5, and if you're paying attention, you can tell when it occurs. Then your engine is a big air compressor.
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11-19-2009, 07:02 AM #19
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Icelandic Silver- 2000 SS / 71 Chevelle 454
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11-19-2009, 07:12 AM #20
An engine is always an air compressor. Only difference is combustion... Unsubscribing..................
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