Forum » General Tuning Discussion » Ej257 Stumble issue (Not the common one)

Ej257 Stumble issue (Not the common one)

General Tuning Discussion

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EJ257... Cobb Intake - Parrin Inlet hose - TGV Deletes - IAG Rails - Parallel lines with an Aeromotive AFPR - ID 1050X injectors. Bigger turbo, forged block and so on.

Having a bit of a hard time nailing down an stumble issue. It occurs with light tip-in between 2000 and 3000RPM. Additionally while lightly accelerating between the aforementioned range. Also, when cursing if there is a light downward grade its quite sluggish when the load drops due to the grade change.

I wanted to make sure my injectors were scaled correctly so I install the factory air box and ran on the factory MAF calibration. The scaling and latency did need a bit of work, but everything is really nice as far as that goes now. Tip-In also seems to be quite happy. The GR STi's had a stumble issue from fuel reversion, but this really isn't the same, there is no notable STFT that accompanies the stumble. Thoughts?


Hi Jordie. You mentioned GR STI, but it was t clear if that’s what you have. if it is, the length, construction of your fuel lines are critical factors as are a few other things.

For now regarding tip in, people often forget to adjust the minimum ipw limit and that can prevent any tip in enrichment from occurring at low deltas if you’ve compensated for increased injector flow vs. stock.

if you’d like to post a log and cal I can take a peak.

Hi Mike,

Thanks so much for the reply. The vehicle in an 09 STi. The lines are (IAG Kit) -6 and are as equal as I could get them on both the supply and return. I'm running 45PSI of base pressure with the manifold reference "T"ed off the Recirc valve . My Tip-In Activation (Min P/W) is currently set to .108.

I literally just reinstalled my Cobb SF intake after having the factory air box in for checking the injector scaling and latency. Still need to flash the MAF calibration and touch it up if necessary. I'll get a log ASAP.

Thanks again!

Sorry for the late reply, I was recovering from a blown back... again. I've attached a log of the AVCS system. One thing I noticed is that the left hand exhaust cam AVCS seems to be having trouble controlling itself. As you can see, its all over the place, reacting slow, then over phasing. Perhaps malfunctioning OCV? I had an issues with the left intake cam a few months ago, it was stuck at 50 degrees, I pulled the OCV, tested and cleaned it which resolved the issues. I guess I'll do the same with the left exhaust OCV. Any other thought would be appreciated.

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