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Old 05-17-2001, 08:12 AM   #1
Keith
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Post Whats the deal with the power surge when you let off the gas?

I know this was talked about before, but I'm lookin for some new info.
Since I have my egt now, I notice that when that power surge happens, the egts spike up about 50 degrees! needless to say, thats not good
So whats the deal? would a better (faster reacting) bov fix that?
Thanks
Keith
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Old 05-17-2001, 10:35 AM   #2
Keith
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Dont make me find you guys in your sleep
Keith
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Old 05-17-2001, 10:44 AM   #3
WRacerX
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Post

Here's my undeducated guess..

The BOV just releases the pressure behind the throttle plate, right? I would guess the surge is caused when the throttle plate snaps shut and the leftover pressure in the intake manifold (other side of the throttle plate) is consumed by the engine as a lean-boosted mixture. So, I don't know how a faster BOV would solve the surge problem. Seems more like an ECU tuning issue.


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Old 05-17-2001, 10:48 AM   #4
blkwag
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I've noticed on my car that the power surge has increased when I switched over to an aftermarket BOV and venting to full atmosphere. I don't know if this has any relevence or not.
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Old 05-17-2001, 11:11 AM   #5
UCI_Scott
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This is not the final answer, but I believe that the RPM increase at clutch-in / lift-throttle is programmed into the ECU to keep emissions low. In general, lift-throttle generates a run rich condition. By taking control over the lift-throttle, the ECU closes the throttle body s l o w l y allowing the fuel/air mixture to remain lean. The RPMs do not rise because the throttle is electronically increased; they rise because the load on the engine decreases while the throttle stays temporarily constant/closes slowly. It may not even be the ECU; it's possible that there is some simple mechanical damper preventing a snap-close of the throttle body.

As for the spike in EGT, I believe it is of little consequence off-power. It's just the system normalizing for a different operating mode. If it spikes when you are on-power it is more of a worry; a glitch in the fuel map or boost map.

--scott
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