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The famous stumble...fixed?


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I have been working on figuring out my fueling issue for a long time (pressure fluctuation). Also hoping to fix that little stumble everyone talks about, but it was not my goal of everything. I have replaced everything. As for mods, I have a built motor internally, FMIC, 18G turbo, Grimmspeed downpipe, up pipe and boost control solenoid.

 

More importantly since this is a fueling issue is the fueling mods:

DW 65C fuel pump

DW 740cc injectors

New OEM in tank fuel filter

Replaced fuel pump and filter O rings twice just to be sure they were good

Had injectors cleaned and tested by DW, passed perfectly

 

I replaced my fuel pressure regulator with a new LGT one from Subaru thinking that was my cause of the fuel pressure fluctuation. Dident help.

 

I came down to the 1 year old DW fuel pump being faulty and started talking to DW. I read and asked them about something I found online saying when you have fueling mods, especially with there DW pumps that they do not like the bypass style regulator that our LGT's and the 08+STI have. I figured I would try one last thing, and found most people with 08+STI replace there regulator with a standard style one, like Automotive, Tomei, or a older gen regulator off a 07 and older STI. Perrin just came out with a nice regulator but they want $300. I got some quick connects from Amazon, and a STI regulator from Subaru and fuel injection hose from Napa. Installed it all like the Cobb Tuning kit is set up, but they want $290 for their kit found here, and I made this for $140. Not only has it fixed my fuel pressure fluctuation, but the stumble that everyone talks about is completely gone. The car accelerates smoother under WOT, the car drives nicer just going with the flow of traffic and using light throttle, all over better.

 

Anyone else ever tried this?

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Edited by SBT
Fixed link to Cobb FPR upgrade kit
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So far still good. Its defiantly better and less noticeable. I tried zeroing the load tables as the STI people suggest, but it kinda seemed to mess with things so I put them back to the original tune. I will do a log and send it to Cryo since he did my tune and make sure everything still looks good. Edited by Brian3676
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what's your correction vs. rpm look like? just wondering if you've moved the stumble. I'd be willing to spend $100 on a Subaru regulator to fix my stumble.

 

I have a stumble at ~1.8k. haven't gotten far enough to try to tackle it yet, but I do hate it. gotta fix my tip-in stumble first...

 

thanks for the info. And the Cobb purchase page has a link to Nasioc (in the reviews) for more info. and that thread has links to other threads, namely one on Romraider, that gives even more specific info.

Edited by Flinkly
* Build Thread * 26.53 MPG - 12 month Average *
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Are you happy with the quality of the Dorman fittings?

 

They seem to work well so far. No leaks, seem well built. I did order a 5th one just as a spare because I dident know, but after getting them and installing, I am not worried at all.

 

Car is still doing well, AF learning does not swing more than +- 1.56%

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Brian3676, I'd still be interested in seeing a plot of your (fuel) Correction vs. RPM from idle to 3k+

 

mainly interested in seeing where your fueling harmonics moved to, since this doesn't appear to be a problem that can be eliminated, just shifted and/or reduced (depending on your "fix").

 

Also, if you have it, a plot of the same thing from before you implemented the STI regulator (to see where your problem RPM area was before).

* Build Thread * 26.53 MPG - 12 month Average *
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I can do a log. I don't have a old one showing with the stock regulator though. It dident move the stumble, it just reduced it greatly. Also somethin to consider, this was with my mods, and my tune. It could be different with stock injectors or other mods.
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very true (on the "random" effects of your fueling mods), hadn't thought of that. Are your per injector compensation tables zero'd out? and what type of headers are you running? OEM?

 

Thanks for the info on reduction vs. shift of the stumble.

 

now I just need to figure out how to justify the $150 expense with my "accountant". hard to justify "fixing" something if it isn't perceived as being broken. Same with getting a DW65C (and new pump housing) to replace my Whinebro...

* Build Thread * 26.53 MPG - 12 month Average *
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im just curious if this is the same "stumble" that i have. seems like somewhat of a misfire at around 2600-3000rpm? as that is a problem i have been having for the past year but never consistantly. i asked here and there but nobody acted like they had a clue what i was talking about. i replaced the pump, one bad coil, spark plugs, and tried using specific brand fuels all with no elimination of the problem. i was thinking maybe an injector problem and was going to send them out for refreshing, but if i can spend the same money and actually fix the problem then im in.
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what's your stumble look like? in logs, like what does your correction+learning look like plotted agains rpm when warm? or your wideband vs. rpm? my afr goes nuts, and correction+learning peaks there. i don't believe i've had a misfire though, and i notice mine most at 1.8k

 

Sent from my XT1028

* Build Thread * 26.53 MPG - 12 month Average *
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bumping this one more time.

 

I think I found the correct Dorman QD which is [ame=http://www.amazon.com/dp/B000CIT1C8]800-120[/ame] not 800-126?

 

and what did Cryo say about the log? He did my tune as well so interested to know if he thinks the mod warrants a retune.

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I posted pics in the orignal post with #'s, but this is the link

 

[ame=http://www.amazon.com/Dorman-800-120-Fuel-Connector/dp/B000CIT1C8]Amazon.com: Dorman 800-120 Fuel Connector: Automotive[/ame]

 

I honestly have been crazy busy, I have not had time to get my laptop and hook it up to do a log. I have my accessport in the car and have a few gauges open, as well as I keep an eye on my wideband. From what I can tell, everything is perfect thus far. My AF learning has never got +- more than a few %, my wideband reads perfect through my entire RPM and boost range.

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only had it on for about fifteen miles, but so far so good, car is as smooth and powerful as its ever been and the part throttle hesitation is gone.

 

made a little bracket that mounts to the shock tower to replicate how it was installed in the cobb install pics.

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