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Old 06-18-2007, 02:12 PM   #1
KSTech
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Member#: 143570
Join Date: Mar 2007
Location: Reno / Sparks, NV
Default Surging on decelleration.. especially downhill...

After installing bigger injectors - Helix 860cc (no other mods at the same time), my car tends to surge (or lightly buck) at about 18-20inHg of vacuum when decellerating and/or going downhill. It is not going in and out of overrun fuel cut like I thought it might be. Injectors are working great at idle, part throttle, and on boost. Fuel trims are pretty much within 5%, except during this decel surging- where they shoot up to +25% and then back down and into the negative and then back up/down again - this is causing the surging. Engine hunts a little bit at idle too, but not too bad.

Any ideas what to do to fix this?

Details: '04 STI with SB GT13 turbo, APS FMIC, Helix 860cc injectors, 1-step cold plugs, Cobb intake, APS BOV, TB exhaust, etc. ECU tuned with Enginuity for the injectors, and a UTEC only for open loop. Approx. 5000 feet elevation (about 12psi atmospheric pressure).
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Old 06-22-2007, 08:36 PM   #2
KSTech
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Location: Reno / Sparks, NV
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bump...

Any help? I think I need to change where the ECU shuts off the injectors when decelerating. Anybody know how to do this?
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Old 06-22-2007, 11:04 PM   #3
Master2192
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Location: Roy, Washington
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98 2.5 RS
04 WRX

Default

Only map I know if is Decel Fuel Resume and that map is only accessible on ECUTek at the moment. What RPMs is this surging happening at? And have you logged throttle percentage during the surging to see if you've got a possible electrical problem?
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Old 06-23-2007, 01:30 PM   #4
KSTech
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Location: Reno / Sparks, NV
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It happens mostly around 3k rpm, but I have felt it from 2500 - 4000.

I logged it versus throttle parameters yesterday. The throttle voltage stays rock steady at around 14V, but the duty cycle is constantly varying from 15% to 25%, and the throttle opening is varying along with the surge by almost 0.5 degrees - 9.02 to 9.41 on one log, and 9.80 to 10.20 on another. Could this small change in angle be felt that much? Could this also be related to my idle hunting too?
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Old 10-11-2007, 08:40 PM   #5
blah0r
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can i buy an 06 hood scoop delete off u?
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