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Old 02-23-2013, 12:51 PM   #26
Airboy
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Quote:
Originally Posted by lancelucas View Post
According to theory, yes, the damper serves a well-intended purpose (absorbing fuel line pulsation). This isn't from the pump being run at partial speed, but rather, from injectors opening and closing and such.

http://www.injector.com/cart/pc/Puls...Dampers-c4.htm
http://injector-rehab.com/shop/fpd.html

Here in the real world, our 4 cylinders do perfectly fine with no ill effects without a damper. The OEM dampers don't do a whole lot and are prone to getting noisy anyways, unfortunately.
I would think the pump being pulsed on/off at 33/66% duty cycle will create pulses in the fuel line as well, at whatever frequency that it is toggling at.
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Old 02-23-2013, 01:05 PM   #27
cummins990
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yes i could see that being an issue also which is why i might try to bypass that. But if the stumbling is due to pulsation or noise and in my case see more noise with dampers. There are others that have seen success with no dampers so I cant see it being an issue.
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Old 02-23-2013, 02:04 PM   #28
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Quote:
Originally Posted by cummins990 View Post
yes i could see that being an issue also which is why i might try to bypass that. But if the stumbling is due to pulsation or noise and in my case see more noise with dampers. There are others that have seen success with no dampers so I cant see it being an issue.
I am sure it works, as far as the issue at 25-3000RPM goes. I am just not sure what potential side effects it would have.
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Old 02-23-2013, 02:17 PM   #29
cummins990
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Yes but wouldn't you see any side affects in the learning view
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Old 02-23-2013, 02:43 PM   #30
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Oops.
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Old 02-23-2013, 02:45 PM   #31
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Quote:
Originally Posted by Airboy View Post
I would think the pump being pulsed on/off at 33/66% duty cycle will create pulses in the fuel line as well, at whatever frequency that it is toggling at.
The PWM output from the fuel pump controller is ~18000 hz. Not a concern.
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Old 02-23-2013, 02:47 PM   #32
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Quote:
Originally Posted by lancelucas View Post

The PWM output from the fuel pump controller is ~18000 hz. Not a concern.
So you don't think the duty cycle fluctuation will make any difference with or without dampers? So no need to bypass?

Last edited by cummins990; 02-23-2013 at 02:55 PM.
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Old 02-23-2013, 02:49 PM   #33
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Originally Posted by cummins990 View Post
So you don't think the duty cycle fluctuation will make any difference with or without dampers? Do no need to bypass?
Correct.
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Old 02-23-2013, 03:16 PM   #34
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Quote:
Originally Posted by lancelucas View Post
The PWM output from the fuel pump controller is ~18000 hz. Not a concern.
That fast eh? Good to know.
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Old 02-23-2013, 10:41 PM   #35
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Originally Posted by Airboy View Post
That fast eh? Good to know.
Fast lil bugger. My rudimentary understanding of the situation thinks that any lower would cause issues with the "audible" range (at least from an OEM designer's perspective).
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Old 03-08-2013, 07:09 PM   #36
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I ended up totally fixing the problem. My comps are all zeroed out and no stumble.

No dampers with an after market FPR. Runs better than ever.
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Old 03-08-2013, 08:12 PM   #37
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The rails with larger injectors + tuning gave me ZERO stumble. Its phenomenal to drive a car that feels normal again
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Old 03-08-2013, 08:14 PM   #38
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Originally Posted by kapp_badbloodz View Post
The rails with larger injectors + tuning gave me ZERO stumble. Its phenomenal to drive a car that feels normal again
Did your tuner zero out your comp tables? If not then it is likely to come back.
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Old 03-08-2013, 08:24 PM   #39
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Quote:
Originally Posted by cummins990 View Post

Did your tuner zero out your comp tables? If not then it is likely to come back.
Hmmm... I didn't. But that's a question I'll ask when I go back. I believe it was but not 100% sure
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Old 03-16-2013, 04:30 PM   #40
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Guys, when you zero the comp tables? Does your ecu still able to make fuel correction? I'm on Cobb race tuner and both my correction and learning wont budge from zero after zeroing out the load comp tables. Any ideas?
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Old 03-16-2013, 04:41 PM   #41
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Zeroing out that table does not effect fuel correction. Sometimes randomly after a reflash the o2 sensor takes a while to warm up. Restart the car and it should come back.
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Old 03-16-2013, 04:56 PM   #42
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Thanks for the quick response. I might have zeroed out the wrong tables since I'm using race tuner. Its under the close loop target load compensation a&b tables. Is it the right one?
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Old 03-16-2013, 05:02 PM   #43
eminehart
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Wrong table.
No its in the sensor calibrations tab.
Load Compensation (Manifold Pressure)(Accel)
Load Compensation (Manifold Pressure)(Cruise)
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Old 03-16-2013, 05:12 PM   #44
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Thank you!
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Old 08-02-2013, 03:54 AM   #45
eagland
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Default 2800 RPM stumble FIXED

Cobb 3.30 map has fix for this issue. I just reflashed ECU with 3.30, it's gone.
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Old 08-02-2013, 10:27 PM   #46
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wait for it........
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Old 08-14-2013, 10:58 AM   #47
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wow thats funny. I spent ~ 4 hours last night datalogging/tuning and fixed the issue (for the most part, i get some stumble below 2k rpms).. I'm going to put on the v3.3 stage 2 map tonight and see if its gone with those maps. I've been reading about this issue for a while and was surprised cobb hadn't came up with a fix yet. I'll post back in a few days and confirm if the studder is gone on my car for the v3.3.
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Old 08-16-2013, 12:20 PM   #48
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yup its fixed. zero stumble and the car seems to run 10x better with v3.3. Read the release notes to try and see what they did but they didn't go into too much detail. Either way my car feels brand new! I did notice they dropped off the peak HP/TQ a decent amount (~10%) according to the release notes, i have yet to do a virtual dyno and see if its true.
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Old 08-16-2013, 03:13 PM   #49
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Cobb 3.31v fixed the stumble and better yet the random "cruise" knock that I have been fighting over a year. I enjoyed driving my car for the first time in a year today. Thanks Cobb for fixing it!
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Old 08-16-2013, 03:41 PM   #50
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Is the stumble going away with custom maps as well as off the shelf maps? I'm curious because I've been pro tuned and my tuner can't get the stumble resolved, So im going the AP route and going to see if the local cobb tuning shop can get my problem fixes. I've got built motor with upgraded Turbo, fuel, Evey thing. I ordered my V3 at the start of the month and am still waiting for them to get more built and shipped out. From what I have read I am hoping that there is something in the software that will help out even with custom tunes.
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