Stumble at idle?
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Joined: Jan 2016
Posts: 89
Likes: 7
From: Chantilly VA
Mine (base m7) does the same. I drove another c7 automatic and it idles similar way. So i concluded that its normal. I also dynoed my car just to make sure. Made 413whp Stock.
Racer
Joined: Jan 2014
Posts: 361
Likes: 5
From: Tampa Bay area Florida
One of the professional forum tuners may comment.
Last edited by LSRX; Apr 17, 2016 at 07:58 PM.
Racer
Joined: Jan 2014
Posts: 361
Likes: 5
From: Tampa Bay area Florida
I would hope so since the engine is 3x or more. However this is not the cause for the "stumble" which has been in my cars intermittent in nature. Actually the stock cam profiles are pretty mild for the displacement of these engines (small duration, wide lobe separation).
I also don't notice this in Ford engines (I own one of those too) In the V8s they are getting almost the same horsepower from a smaller displacement engine. I guess they have Camry camshafts.
Still looking forward to a "professional" tuner to respond or someone that swapped out the injection for a carburetor without a cam modification (hard to find) to prove the point.
I also don't notice this in Ford engines (I own one of those too) In the V8s they are getting almost the same horsepower from a smaller displacement engine. I guess they have Camry camshafts.
Still looking forward to a "professional" tuner to respond or someone that swapped out the injection for a carburetor without a cam modification (hard to find) to prove the point.
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St. Jude Donor '07-'08-'10, '14
I would hope so since the engine is 3x or more. However this is not the cause for the "stumble" which has been in my cars intermittent in nature. Actually the stock cam profiles are pretty mild for the displacement of these engines (small duration, wide lobe separation).
I also don't notice this in Ford engines (I own one of those too) In the V8s they are getting almost the same horsepower from a smaller displacement engine. I guess they have Camry camshafts.
Still looking forward to a "professional" tuner to respond or someone that swapped out the injection for a carburetor without a cam modification (hard to find) to prove the point.
I also don't notice this in Ford engines (I own one of those too) In the V8s they are getting almost the same horsepower from a smaller displacement engine. I guess they have Camry camshafts.
Still looking forward to a "professional" tuner to respond or someone that swapped out the injection for a carburetor without a cam modification (hard to find) to prove the point.
I really dig the coyote motor, but there's nothing like a little rumble!
Race Director
Joined: Jul 2007
Posts: 10,961
Likes: 2,643
From: Texas Hill Country
I have a 2015 Mustang GT (Coyote motor) and agree it is VERY smooth, but also a DOHC motor and realistically a completely different animal. The big ol pushrod motors do just rumble a bit more (even with the stock cam) and is pretty much normal.
I really dig the coyote motor, but there's nothing like a little rumble!
I really dig the coyote motor, but there's nothing like a little rumble!
My C5 Z06 and my C7 when it was stock both had/have a little lump to them but hey what do I know? Maybe someone should post a video so we know what they are talking about in the first place.
Last edited by Higgs Boson; Apr 18, 2016 at 09:44 PM.
Racer
Joined: Jan 2014
Posts: 361
Likes: 5
From: Tampa Bay area Florida
I have a 2016 GT and while it idles smooth, it varies RPM more like it's working a lot harder to adjust which is quite annoying.
My C5 Z06 and my C7 when it was stock both had/have a little lump to them but hey what do I know? Maybe someone should post a video so we know what they are talking about in the first place.
My C5 Z06 and my C7 when it was stock both had/have a little lump to them but hey what do I know? Maybe someone should post a video so we know what they are talking about in the first place.
My opinion is that it is just due to the way GM software commands fueling for the engine and is not out of the ordinary. This may be able to be tuned out or it may not. If it can't be tuned out due to the way the engine management system operates, only an alternate method(carburetor or aftermarket fueling system would achieve anything different.
Race Director
Joined: Jul 2007
Posts: 10,961
Likes: 2,643
From: Texas Hill Country
I believe what the OP is talking about is an intermittent stumble at idle. The engine will run smooth for x amount of time, which changes from time to time, and then stumbles a bit.
My opinion is that it is just due to the way GM software commands fueling for the engine and is not out of the ordinary. This may be able to be tuned out or it may not. If it can't be tuned out due to the way the engine management system operates, only an alternate method(carburetor or aftermarket fueling system would achieve anything different.
My opinion is that it is just due to the way GM software commands fueling for the engine and is not out of the ordinary. This may be able to be tuned out or it may not. If it can't be tuned out due to the way the engine management system operates, only an alternate method(carburetor or aftermarket fueling system would achieve anything different.
If it isn't just OCD tach watching, then there are a lot of things that happen like AC compressor going on/off/engage/disengage, evap system actuation, etc not to mention rising IATs (and maybe also ECT) while sitting at idle and of course there will be corrections for that. The torque based ECMs used today will move the throttle blade a degree or two at idle, move spark lead around, etc to maintain a desired idle torque level. Gone are the days of a set spark and a set TB blade. It's all dynamic now in pretty much all cars that I know of.
Melting Slicks
Joined: Sep 2009
Posts: 2,180
Likes: 233
From: Minnetrista Minnesota
Racer
Joined: Jan 2014
Posts: 361
Likes: 5
From: Tampa Bay area Florida
Is it a stumble one can actually feel, as in butter smooth then it acts like it misses and then gets smooth again? Or are we talking about the tachometer moving? I would not be surprised if some cars have "smoothed" tachs that don't show minor discrepancies. My Mustang tach also will hold an RPM, drop 100, hold, raise 100, hold, raise another 100, hold, etc. It isn't smooth if that's what we are talking about.
If it isn't just OCD tach watching, then there are a lot of things that happen like AC compressor going on/off/engage/disengage, evap system actuation, etc not to mention rising IATs (and maybe also ECT) while sitting at idle and of course there will be corrections for that. The torque based ECMs used today will move the throttle blade a degree or two at idle, move spark lead around, etc to maintain a desired idle torque level. Gone are the days of a set spark and a set TB blade. It's all dynamic now in pretty much all cars that I know of.