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I am also experiencing the stumble on my 08 with Stage 2 Cobb OTS 91 map.

I have all sorts of questions, but the weirdest one is:

Has anyone seen a connection with the stumble and throwing CEL P0172 (system too rich bank 1)????

I noticed the stumble was particularly bad on morning then my car started sputtering around 3800rpm and eventually died. I turned it back on, reset the code, and not seen it again in a month, BUT, now I feel the stumble more than ever.

Any help or advice would be appreciated!
 

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I chased the dreaded stumble for over a year with two different tuners. I tried the fuel line extension, changing to the GD regulator set-up, an aftermarket regulator, and at least half a dozen tuning tweaks along the way to try to get rid of it. Replacing the fuel rails was what solved it 100%.

Essentially, changing the rails treated the disease, everything else was treating the symptoms. Other people may have had better luck with the cheaper changes, but for my car none of them worked out.
My tuner said fuel rails wernt needed. I am having radium engineering use my car to test using special pulse dampning bits on their fuel rails to help cure the stumble. I have tried everything else so far.
 

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I was having the same issue with my 11 with stage 2 and threw that code. It was hesitating bad at about the same RPM as you. Turned out to be my plugs. Changed them out and all was better. Could also be a bad coil pack too. I would start with your plugs first. But you can also check your MAF sensor, front 02 sensor, fuel delivery, intercooler hose that connects to the turbo, or check for boost leaks. That's normally what will cause the P0172 code.

I am also experiencing the stumble on my 08 with Stage 2 Cobb OTS 91 map.

I have all sorts of questions, but the weirdest one is:

Has anyone seen a connection with the stumble and throwing CEL P0172 (system too rich bank 1)????

I noticed the stumble was particularly bad on morning then my car started sputtering around 3800rpm and eventually died. I turned it back on, reset the code, and not seen it again in a month, BUT, now I feel the stumble more than ever.

Any help or advice would be appreciated!
 

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No prob! Make sure you check the gap on the plugs. Sometimes they aren't pre gapped correctly like they claim to be. These cars are very finicky when it comes to spark plug gap.
 

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I've noticed the stumble more with stage 2+. Only at slow acceleration. I bought a GD style fuel line kit from funks here off the forum. I'm waiting for a pro-tune to see if it goes away.
 

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Same thing as mac_sti (S2) - after I did the GD fix and got a TorquedPerformance.com eTune (used to be on a Cobb S2 OTS tune ACN91), problem fixed for me. The stumble was annoying and it also happened on slight acceleration for me (because I knew what it was when it happens - lol).
 

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I've noticed the stumble more with stage 2+. Only at slow acceleration. I bought a GD style fuel line kit from funks here off the forum. I'm waiting for a pro-tune to see if it goes away.
Did this work for you? I am one in the larger injector group...wondering if rails are the only fix.
 

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Jack - my tuner feels pretty confident he can do the same. First map was rough, second revision smoothed it out considerably. Hoping the 3rd will do the trick. Just in case, I'm starting the research...
 

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Thought I would chime in. I do have the 3 foot mod. I had a etune from tp stage 2 for a long time, and car ran very well. Just got tuned for e85 w id1000, dw65c, ebcs. I think I still have the stumble in first gear only. 2-6 is fine. At partial throttle I can feel the stumble in first gear. At full throttle I do not have stumble. Kinda weird. Maybe ecu is still in learning mode, as I heard it takes several start cycles for it to learn.
 

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Thought I would chime in. I do have the 3 foot mod. I had a etune from tp stage 2 for a long time, and car ran very well. Just got tuned for e85 w id1000, dw65c, ebcs. I think I still have the stumble in first gear only. 2-6 is fine. At partial throttle I can feel the stumble in first gear. At full throttle I do not have stumble. Kinda weird. Maybe ecu is still in learning mode, as I heard it takes several start cycles for it to learn.
It should take a day or two to learn. If it continues take it back to the tuner.
 

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Thought I would chime in. I do have the 3 foot mod. I had a etune from tp stage 2 for a long time, and car ran very well. Just got tuned for e85 w id1000, dw65c, ebcs. I think I still have the stumble in first gear only. 2-6 is fine. At partial throttle I can feel the stumble in first gear. At full throttle I do not have stumble. Kinda weird. Maybe ecu is still in learning mode, as I heard it takes several start cycles for it to learn.
Did you go with Eric to tune for these mods? Pretty sure he requires a fuel pressure regulator when upgrading injectors and pump for this very reason. He may just require it because he is tuning remotely and needs consistency while doing so and if you protuned locally they may not require it (my local tuners don't). I'm currently on his Stage 2 tune (LOVE IT) and have id1000s and walbro 255 taking up shelf space at the moment. Gotta get the FPR and I'll be ready for some of that corn juice goodness!
 

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Great thread. I had the stumble to a noticeable level on stage two but it was when I went to ELH that the stumble became annoying. I am currently running the fuel hose extension mod and this was a night and day transformation. Engine running was so much smoother straight away. Graham at boosted performance did some fine tuning on slight throttle and boost transitions and it is now it is smooth. The extra tuning may have been needed due to header design though or perhaps early symptoms of a ringland failure.

So now I am about to swap to a built engine and want to clean up the fuel hose. I have bought a Sard FPR but can't find clear instructions about how to install. To make matters worse I have seen where some people leave the stock setup in place in addition or swap and install a GD dampener along with the aftermarket FPR.

I would like to just install the Sard without any other dampeners if it will work but above all else I just want a smooth system.

Any ideas and suggestions?
 
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