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How To Tune To Stop Flutter/bovs Causing Stalling.

Rolls

By Rolls,
in Engines & Forced Induction

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89CAL Grand Master

89CAL

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Let me understand then what exactly is happening on throttle off. When you come off boost and shut the throttle the air will revirb back and flow through the recirc pipe back into the turbo and stay in the system. Correct? Ok now lets say, just for simple example, the car measured 10 litres of air coming in and allowed 200ml of fuel to be added for this air. The engine does its cycle on boost, burns 8 litres of air and 100ml of fuel. You back off the throttle and the plate shuts with this 2 litres of air still in the intake before the throttle and 100ml of fuel for the counted air. To prevent the car from stalling is this where the AAC valve kicks in? Since the throttle is closed you are going to need to let this air come in to burn this fuel to keep the engine on and from stalling. My car for the last week has been stalling its nut when I come off boost and let the revs drop. I am running a full recirc system.

What is the cause of this stalling state? Ive cleaned the AAC but have not taken it for a drive yet. Am I right when I am saying the engine is using the AAC to let in this air to burn off this fuel? When the throttle is shut, obviously air isnt going to get in there but if there is fuel in the piston its going to need air to burn...

If you have an O2 sensor (wideband) in when this is happening you can see what the engine does. Desired AFR > Close throttle body> momentarily rich then full lean (deceleration, no problem). So as GTSBoy said, no part is played by your AAC valve. The engine doesnt need power during deceleration so it doesnt inject any fuel at all and doesnt really need any air. When the car returns to an idle state it will open the AAC valve and use the air feed from there.

As for Rolls question about "how did nissan tune out the stalling issue". Remember that the cars were designed like that (the ones without bov's) so it wasnt so much "tuning it out" as much as tuning the car to suit. As far as I know the introduction of BOV's was an emission thing as well as helping with spool times between gear changes, was supposed to be an improvement and hence the ECU was tuned to suit. running no BOV confuses the AFM from what I know, as it see's air flowing in the wrong direction.

I run an aftermarket BOV plumback, purely because I hate the sound of the standard BOV's, annoyed the hell out of me. So I will never argue that they dont work etc, but I dont see myself ever running one again

Edited by 89CAL
DVS JEZ Grand Master

DVS JEZ

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89CAL u are right about the decelleration. But his issue isnt on decel as such its when it returns to idle after decel, thats when it drops the rpm too low and stalls the engine

Rolls Grand Master

Rolls

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As for Rolls question about "how did nissan tune out the stalling issue". Remember that the cars were designed like that (the ones without bov's) so it wasnt so much "tuning it out" as much as tuning the car to suit.

How does one tune it to suit then?

89CAL Grand Master

89CAL

Posted
Posted

How does one tune it to suit then?

The ones running without BOV's at all were probably tuned similar to what your standard R33 is (I dont know which cars these are so cant say to much)

You can get away with NO BOV from what I remember, but its at least alot easier then running an atmo BOV

but as Paul said, just a matter of driving around, finding the cells were its pumping fuel in and adjusting to bring it back to a normal AFR.

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