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#11 | |
![]() Join Date: Jun 2006
Location: Sparks, NV
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90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold. |
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#12 |
![]() Join Date: Jan 2006
Location: Decatur, AL
Posts: 1,112
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Hi, to clarify, the IAC is at 150 on start then comes down. When the first start happens and it dies, the IAC count is still around 80-100. I just finished replacing both fuel pumps again...they were new Airtex, I went with Delco pumps this time, no significant change, I have maybe three more psi at all ranges with the new pumps...no change in leakdown. What I wonder about is the requested RPM before start that shows 3000K plus requested but first revolution in crank sequence brings requested RPM immediately down to 875. Car runs rough in back up fuel and I wonder if the back up fuel controls the initial start up air and spark until the ECM sees 400+ RPM? I have asked Haibeck about this and he says he has never encountered this issue before . He initially wondered about the spark retard on start up, but pulled the knock sensor clip off so that wasnt the issue/. He also asked if I had another ECM to swap..I don't, he also asked if my Tech1 was giving accurate readings..well pulled out the old Tech1 with a different Mass Storage Cartridge and I got the same readings ( I found an old Vetronix rep that was selling out and I bought all his extra Tech1 stuff).
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Corvette95 Registry and Forum (*************) 1989 C4 Conv Wht/Gry Auto Hardtop Top Flight SOLD 1995 C4 Coupe Purple/Blk 6 Speed 1989 C4 Conv Wht/Red Auto SOLD 1996 C4 Conv Black/Tan Auto SOLD 1994 C4 Coupe Wht/Blk SOLD 1995 C4 ZR-1 White/Gry #278 Dual Dunn Head SOLD 1986 C4 Coupe Black/Red 4+3 SOLD 1990 C4 ZR-1 Red/Red #0454 Last edited by Corvette95; 08-14-2020 at 01:01 PM. |
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#13 |
![]() Join Date: Feb 2013
Location: New Concord Kentucky
Posts: 179
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Ok so the iac is at 80 - 100 at the stall? So as stated adjust the throttle blades further open, I normally shoot for 20- 30 iac counts on a hot idle, some may disagree but thats that. With kr on start up, common lt5 is mechanically noisey, that normally goes away fast. Since you said it is the first start only the car light off reduction is probably active, between 20 and 32 c coolant temp from memory, so it is certainly reducing engine efficiency, a simple change to that will help out with no more sustained negative spark. Outside of those temp ranges there is no spark reduction from the light of feature. After having the engine ported, why no tune, just as a matter of interest.
Graham |
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#14 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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Graham,
I believe you meant he should CLOSE throttle blades so more bypass is needed to run motor. At 0 IAC counts, the IAC is fully closed. By closing blades the ECM would have better control over idle speed. I shoot for 12- 20 steps, again on a hot idle.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX |
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#15 |
![]() Join Date: Feb 2013
Location: New Concord Kentucky
Posts: 179
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Well 1 says it goes to zero and one says it is at 80 so both maybe true. Thats why I said a warm idle iac value
Graham |
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#16 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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Usually, for me, if the IAC at operating idle is at 0, either the blades are open too wide or there?s a vacuum leak. With a ported top end and rebuilt TB, I suspect Chris? motor is moving more air thru the TB, so closing the blades would bring up the IAC counts.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX |
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#17 |
![]() Join Date: Jan 2006
Location: Decatur, AL
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Thank you SO much for the feedback. I will data record from the IAC tomorrow and post results. I will record the live IAC data from cold start in the morning and post! Thanks again .
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Corvette95 Registry and Forum (*************) 1989 C4 Conv Wht/Gry Auto Hardtop Top Flight SOLD 1995 C4 Coupe Purple/Blk 6 Speed 1989 C4 Conv Wht/Red Auto SOLD 1996 C4 Conv Black/Tan Auto SOLD 1994 C4 Coupe Wht/Blk SOLD 1995 C4 ZR-1 White/Gry #278 Dual Dunn Head SOLD 1986 C4 Coupe Black/Red 4+3 SOLD 1990 C4 ZR-1 Red/Red #0454 Last edited by Corvette95; 08-15-2020 at 05:40 AM. |
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#18 |
![]() Join Date: Jan 2006
Location: Decatur, AL
Posts: 1,112
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FYI IAC drops from 150 to under 100 after first start then close to near zero after successful start after first. I think this a pre program open loop issue. Can this be tuned out. Will update Saturday morning. Thanks to all!
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Corvette95 Registry and Forum (*************) 1989 C4 Conv Wht/Gry Auto Hardtop Top Flight SOLD 1995 C4 Coupe Purple/Blk 6 Speed 1989 C4 Conv Wht/Red Auto SOLD 1996 C4 Conv Black/Tan Auto SOLD 1994 C4 Coupe Wht/Blk SOLD 1995 C4 ZR-1 White/Gry #278 Dual Dunn Head SOLD 1986 C4 Coupe Black/Red 4+3 SOLD 1990 C4 ZR-1 Red/Red #0454 Last edited by Corvette95; 08-15-2020 at 05:38 AM. |
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#19 |
Join Date: May 2007
Location: Chicagoland, IL
Posts: 9,697
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I think you should do the Min Air adjustment before doing anything else IMO.
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[SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX |
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#20 | |
![]() Join Date: Jan 2006
Location: Decatur, AL
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Corvette95 Registry and Forum (*************) 1989 C4 Conv Wht/Gry Auto Hardtop Top Flight SOLD 1995 C4 Coupe Purple/Blk 6 Speed 1989 C4 Conv Wht/Red Auto SOLD 1996 C4 Conv Black/Tan Auto SOLD 1994 C4 Coupe Wht/Blk SOLD 1995 C4 ZR-1 White/Gry #278 Dual Dunn Head SOLD 1986 C4 Coupe Black/Red 4+3 SOLD 1990 C4 ZR-1 Red/Red #0454 Last edited by Corvette95; 08-16-2020 at 09:58 AM. |
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