Help with 3rd Gear Low RPM, Low Acceleration Stuttering/Rocking
09-30-2010, 09:43 PM
#1
1st Gear Member
Thread Starter
Join Date: Sep 2010
Location: MI
Posts: 69
Help with 3rd Gear Low RPM, Low Acceleration Stuttering/Rocking
Hey,
I just got an 04 Mustang GT. It's got a K&N Cold Air Intake and some Magnaflow cat-backs. I've noticed some stuttering when I'm accelerating in 3rd gear. It's almost as if the car is rocking back and forth. I'm only at around 2000 RPM when it happens. I'm not really giving it too much throttle, just enough to get up to 45 or 50 mph (just normal acceleration). It doesn't happen when I give it more gas (around half-way down on the pedal). I notice it a little bit in 4th gear too, when I give it the same amount of gas. I guess maybe I just notice it more in 3rd because I accelerate a certain way in 3rd to get up to speed. Any ideas of what it might be or simple things I can check for? Maybe something with the intake or the fuel system? Thanks for any help!
I just got an 04 Mustang GT. It's got a K&N Cold Air Intake and some Magnaflow cat-backs. I've noticed some stuttering when I'm accelerating in 3rd gear. It's almost as if the car is rocking back and forth. I'm only at around 2000 RPM when it happens. I'm not really giving it too much throttle, just enough to get up to 45 or 50 mph (just normal acceleration). It doesn't happen when I give it more gas (around half-way down on the pedal). I notice it a little bit in 4th gear too, when I give it the same amount of gas. I guess maybe I just notice it more in 3rd because I accelerate a certain way in 3rd to get up to speed. Any ideas of what it might be or simple things I can check for? Maybe something with the intake or the fuel system? Thanks for any help!
09-30-2010, 09:53 PM
#2
5th Gear Member
Join Date: Aug 2007
Location:
Posts: 3,189
sounds like your missing, got a CEL on?
you should probably go ahead and replace the spark plugs anyways since you don't know when they were done last, and check the plug wells for antifreeze/water. if its still doing it after that, probably a bad cop.
you should probably go ahead and replace the spark plugs anyways since you don't know when they were done last, and check the plug wells for antifreeze/water. if its still doing it after that, probably a bad cop.
10-01-2010, 08:58 AM
#4
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Was the MAF screen removed when the K&N intake was installed? If it's not there then it was removed...
On the OEM intake there is, sandwiched between the airbox and the MAF housing flange, a stainless steel mesh screen that straightens out the air flow through the MAF so the the small sample of flow actually measured by the MAF sensor is a solid representation of the total flow.
With this screen removed (as is often done by those that believe it to be a restriction¹), and at lower flows, the sample measured by the sensor may not be representative of the total flow--the PCM doesn't know this of course and therefore calculates an inappropriate injector pulse width, the a/f mix is then too rich or too lean, and the engine stumbles.
One other possibility for the issue you describe is a stuck or sticking EGR valve--but I'd check for the presence of the MAF screen first...
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¹ - The MAF screen does not present any restriction--click here for more about that--nor is it there to "prevent debris" from getting into the MAF as I have seen put forth. I often wonder what those that make that claim think the air filter is there for?
On the OEM intake there is, sandwiched between the airbox and the MAF housing flange, a stainless steel mesh screen that straightens out the air flow through the MAF so the the small sample of flow actually measured by the MAF sensor is a solid representation of the total flow.
With this screen removed (as is often done by those that believe it to be a restriction¹), and at lower flows, the sample measured by the sensor may not be representative of the total flow--the PCM doesn't know this of course and therefore calculates an inappropriate injector pulse width, the a/f mix is then too rich or too lean, and the engine stumbles.
One other possibility for the issue you describe is a stuck or sticking EGR valve--but I'd check for the presence of the MAF screen first...
--------------------------------------------
¹ - The MAF screen does not present any restriction--click here for more about that--nor is it there to "prevent debris" from getting into the MAF as I have seen put forth. I often wonder what those that make that claim think the air filter is there for?
10-01-2010, 04:21 PM
#6
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Likely increased intake noise, it's more or less in synchronisation with the exhaust making it difficult to localise.
It would also slightly, and variably as the intake flow changes, alter the MAF transfer function which would cause AFR and load calculations (and therefore timing) to change a bit.
It would also slightly, and variably as the intake flow changes, alter the MAF transfer function which would cause AFR and load calculations (and therefore timing) to change a bit.
10-02-2010, 07:01 PM
#8
Join Date: Sep 2008
Location: CO
Posts: 48
Likely increased intake noise, it's more or less in synchronisation with the exhaust making it difficult to localise.
It would also slightly, and variably as the intake flow changes, alter the MAF transfer function which would cause AFR and load calculations (and therefore timing) to change a bit.
It would also slightly, and variably as the intake flow changes, alter the MAF transfer function which would cause AFR and load calculations (and therefore timing) to change a bit.
10-03-2010, 11:28 AM
#9
3rd Gear Member
Join Date: Mar 2009
Location: NOLA
Posts: 665
i'm gonna hafta agree with the spark plug guys. i had the same exact thing happen two weeks ago and new plugs fixed the problem. same thing happened with my f150 a while back as well. and he's not in too high of a gear if you're nearing 2k rpms when you notice the problem. another good way to make sure is to get on it a little bit, and make sure when you shift into 3rd, you're doing over 3k rpms. if the syptoms are unnoticeable at this point, you're most likely experiencing a miss at high load/low rpm.
10-03-2010, 02:35 PM
#10
1st Gear Member
Thread Starter
Join Date: Sep 2010
Location: MI
Posts: 69
The CEL is not on. Also, the guy that owned it before me replaced the spark plugs less than a year ago. He took pretty good care of the car. I don't notice it when I shift into 3rd at a higher RPM and when I'm giving it more throttle. It's just when I'm driving around casually that it happens.