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Old 01-15-2012, 04:52 PM   #1
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Default MAP under fuel decel

Whats your map value around when you go under fuel decal cut?
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Old 01-16-2012, 01:26 AM   #2
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Right around 13 kPa.
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Old 01-16-2012, 01:32 AM   #3
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Yeah, just checked some old logs and saw 12-14 kPa.

Sidebar: I just realized that it's been just about two years at this point since I've datalogged a car. Been driving on a stock ECU for that whole time. Something must be done to change this...
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Old 01-16-2012, 02:11 AM   #4
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How is your setup done for the Idle valve? Plumed into the intake piping? Also does it hold down at those areas though out the area when coming down until fuel cuts back in.
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Old 01-16-2012, 02:19 AM   #5
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Quote:
Originally Posted by Techsalvager View Post
How is your setup done for the Idle valve? Plumed into the intake piping?
No, my car uses DEI, so the idle valve is plumbed into the downpipe just after the turbine outlet, between the recombinant valve and the uptake diverter.


Quote:
Also does it hold down at those areas though out the area when coming down until fuel cuts back in.
Fuel cut has nothing to do with manifold vacuum. It's simply a function of an engine turning at high RPM trying to suck air against a closed throttle plate.


Here's a little snapshot of a log:



At the left, I've just taken my foot off the pedal after some full-throttle acceleration. TPS and MAP both fall to the bottom of the scale immediately, while RPM begins to decrease gradually. You can see that as RPM falls, MAP eventually begins to increase slightly. Then I push in the clutch and shift into neutral, allowing RPM to fall faster, and MAP to rise slightly faster. Then there's a sort of hump where you can see the idle valve starting to do its thing, (RPM fell a bit too much here, suggesting that this log was taken from before I sorted that all out) at which point RPM rises, followed by a slight drop in MAP as the idle valve closes a bit, and things then stabilize.
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MAP under fuel decel-kwmtq.gif  

Last edited by Joe Perez; 01-16-2012 at 02:29 AM.
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Old 01-16-2012, 03:10 AM   #6
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Ive got mine much higher, arround 24kpa. I dont see any ill effects but im very new to this. I recall reading somewhere that it should be set 4-5kpa below the lowest u see at idle ( could be from when i had a Miata link ecu). Feel free to enlighten me if 24 is stupid / could be causing issues.

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Old 01-16-2012, 03:23 AM   #7
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Boy, did I misinterpret the meaning of this thread the first time around. OP was asking what value we had specified under "Over Run Fuel Cut." I thought he was asking what actual MAP values we were observing under deceleration.

The exact number used is not critical; it just needs to be lower than the lowest value you expect to see under sustained light-load cruise, yet slightly higher than the actual MAP values observed during deceleration. I set mine to 20.
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Old 01-16-2012, 04:54 AM   #8
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Quote:
Originally Posted by Joe Perez View Post
Boy, did I misinterpret the meaning of this thread the first time around. OP was asking what value we had specified under "Over Run Fuel Cut." I thought he was asking what actual MAP values we were observing under deceleration.
I am asking for the actual values seen unde decal fuel cut.
Really be helpful to see peoples datalogs and know how their idle valve is plumped into the system.
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Old 01-16-2012, 04:56 AM   #9
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It varies with RPM and compression, but 12-15kpa. Fresh motors are 16-17kpa, and I consider them "broken in" when I see 13-14kpa. I typically set overrun at 20-22kpa - the slightest crack in the throttle will typically bring it up to around 25-28kpa.
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Old 01-16-2012, 06:19 AM   #10
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Quote:
Originally Posted by Techsalvager View Post
I am asking for the actual values seen unde decal fuel cut.
Really be helpful to see peoples datalogs and know how their idle valve is plumped into the system.
The idle valve plumbing will make no difference to MAP values, if it's bleeding air in, it's bleeding air in, both plumbed into the intake tract and not it's pre throttle body.
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Old 01-16-2012, 12:11 PM   #11
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I see a difference. Before with the IAC enabled and working usually it would hover around 20s coming though decel fuel cut.

With closed loop idle turned off and a cap over the IAC opening I pull all the way to 13s, probably lower then 13s considering that 13 is the limit of the map sensor iirc.

Just trying to check all the variables.
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Old 01-16-2012, 01:16 PM   #12
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I'm struggling to understand why you keep mentioning the decel fuel cut function. Are you positing that one is likely to observe different MAP values while decelerating in gear with the throttle closed based on the setting of that particular software variable?
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Old 01-16-2012, 01:25 PM   #13
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Quote:
Originally Posted by Joe Perez View Post
Are you positing that one is likely to observe different MAP values while decelerating in gear with the throttle closed based on the setting of that particular software variable?
Quite possibly yes on observing different map valus while decelerating in gear with the throttle closed.
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Old 01-16-2012, 05:32 PM   #14
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Quote:
Originally Posted by Techsalvager View Post
I see a difference. Before with the IAC enabled and working usually it would hover around 20s coming though decel fuel cut.

With closed loop idle turned off and a cap over the IAC opening I pull all the way to 13s, probably lower then 13s considering that 13 is the limit of the map sensor iirc.

Just trying to check all the variables.
Capping the valve is NOT the same as plumbing it into the intake tract!
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Old 01-16-2012, 05:50 PM   #15
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I capped the valve to make sure it wouldn't leak when I turned off idle control.
Normally I ran it without it plumed into the intact tract.
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Old 01-16-2012, 06:17 PM   #16
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Ok, but having it plumbed into the intake or not plumbed will produce identical results.
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Old 01-16-2012, 06:19 PM   #17
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so far yes it seems to be so, though with it disabled it seems on my car atleast I can pull map down further on decel.
That and I can idle better so far around 15.2+-2 at 900rpms and 27kpa. Just research. Thinking my megasquirt isn't doing a great job with the idle valve.
I did notice with it open to atmo compared to connected to the intract tract that the car rev up better from idle.
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Old 01-16-2012, 07:25 PM   #18
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MS1 or MSII? There's a whole raft of changes to the MSII code over the last moth or so which makes its idle valve control much much better, virtually OEM when tuned properly....
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