2500rpm stumble?

[OldManSTI]

Okay folks, what is this "2500rpm stumble" I've seen mentioned in a few posts? I have noticed a hesitation (although stumble would be a good descriptor as well) in my STI around that RPM range. I merely assumed it was the "Intelligent Mode" I was in attempting to save me some gas or something.

If this is a common problem, what is the solution?

 

[Boogieman98]

I assume you have a 08-14 model. Good tune or you can change the fuel dampers to the ones that were on the older models

 

[Spamby]

Funny that this was brought up today. I was doing some more reading on the subject this morning.

supposedly this is more of annoyance than a detriment to the car. At a certain rpm and load, there is a resonance or reverberation in the fuel lines due to the configuration of the FPR, fuel dampers and fuel lines themselves. It has been described as a water hammer effect.
Im not so sure that the true problem is the tune alone but more so the hardware or fuel line/damper/FPR configuration in conjunction Tuning alone I don't think eliminates this as the underlying issue is the hardware. Tuning can be performed to lessen the effect but as I'm gathering, I don't think it truly rids it of the problem.
Converting to a GD style FPR and fuel line or creating one of your own, but eliminating the dampers in the process, is the only measure that seems to fix this 100%. Of course, tuning is going to be needed after the fuel line setup has been done

 

[Boogieman98]

I didn't know you could eliminate the dampers. What do they look like again? Maybe I can do that before Holycrapitsfast and I attack the 93 tune

 

[Spamby]

Motherpussbucket ... load compensation tables! :tard:

 

[Spamby]

So it seems your going to zero out your load compensation tables (cruise/accel) and go with a GD style FPR/fuel line setup. [MENTION=1868]Boogieman98[/MENTION]
You'll want to remove your entire setup FPR, dampers and fuel lines and replace them with the GD setup, which is basically the FPR and fuel line.
There are few places that sell kits. Cobb has one for 290 but that seems outrageous for a fuel line and factory GD FPR.

 

[OldManSTI]

So it's a design flaw. Fabulous! I've seen the kit on Cobb's site, but never looked into it to see what it was. Thank you for the info [MENTION=1507]Spamby[/MENTION]

 

[HolyCrapItsFast]

I'm coming into this conversation a little late and I only glossed over what was said but thus far it has been my experience that the stumble is affected more by MAF scaling in combination with Load Compensations. The fuel system in the GR and later are different enough to make the issue worse than the GD, but I believe it is not the underlying cause. That said, the GD is by no means immune to this condition. The stumble often comes when you do any kind of modification to the intake tract such as an intake, turbo inlet, turbo upgrade, FMIC or larger TMIC or TGV deletes.

In almost 100% of all cases I was able to eliminate the stumble with a tune and by adjusting the MAF and applying Load Compensation. I am not saying that the GD fuel mod won't help and I have seen it work in most cases but the load comp tables in the GR look like they are compensating for something, but I don't know what. I feel that is half the problem along with a poorly defined fuel map and the fuel dampers.

In other words... The root cause needs to be discovered because there is no "one clear answer" and if some one tells you there is, then they are trying to sell you something. :tup:

@OldManSTI You payed for a premium membership. This entitles you to a tune and if you have the stumble, Then you might want to consider taking advantage of that.

 

[OldManSTI]

Roger that [MENTION=9]HolyCrapItsFast[/MENTION]. I'm saving my tune for when I upgrade my TBE, but I will be hitting y'all up for that tune.

 

[IGOTASTi]

Roger that @HolyCrapItsFast. I'm saving my tune for when I upgrade my TBE, but I will be hitting y'all up for that tune.

He does awesome work [MENTION=4899]OldManSTI[/MENTION].

 

[Boogieman98]

How many tunes do platinum members get?

 

[Alin]

How many tunes do platinum members get?

Unlimited. :tup:

 

[OldManSTI]

Unlimited? [MENTION=1172]Alin[/MENTION], this platinum thing just gets better!

 

[Boogieman98]

Got to love the perks

 

[Boogieman98]

I had a thought the other night about this. So I do not get that stumble on my e-85 tune ( Thanks Holycrapitsfast ) but I do on my 93 tune. Now I know the injector duty cycle is more on the e-85 tune as it is pushing more fuel through the injector, so it got me thinking about fuel pressure. Has anyone ever tried to drop or raise the fuel pressure from stock and tune the car to see if that helps? I dont know anything about tuning but it would seem to me that we could lower fuel pressure, increase injector duty cycle and what ever else is needed and that might relieve the stumble issue. Again just a thought.

 

[HolyCrapItsFast]

Adjusting the fuel pressure may very well do the trick but that needs to be tested. Seems like a good experiment :tup:.

I would only do this for larger size injectors though. If you lower the pressure on stock injectors you will likely see IDC dangerously high during WOT.

 

[Boogieman98]

Well if we still get the stumble on 93 oct with your tune once we get done then maybe I can be the test dummy. Oh and no stumble yet on your base map by the way.

 

[HolyCrapItsFast]

Well if we still get the stumble on 93 oct with your tune once we get done then maybe I can be the test dummy. Oh and no stumble yet on your base map by the way.

If you are not seeing a stumble now then you will likely never see it.

 

[Alin]

If you are not seeing a stumble now then you will likely never see it.

:bow: :ty: :bigtup:

 

[Boogieman98]

And all it took was an e-tune. No more pro tunes for me