Author Topic: Deceleration enrichment query  (Read 5463 times)

Offline BenFenner

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Deceleration enrichment query
« on: February 08, 2008, 10:56:55 pm »
Does VEMS have deceleration enrichment?
Can negative values be used in the AE section to accomplish something similar?

I ask because I'm getting to the point where I drive for a while and I forget I'm running stand-alone (which is a very good thing). One of the few things that remind me, is the jerk experienced when letting off the throttle. I run quite lean during cruising ~1.05 and this obviously makes things worse, but I'd like to have decel enrich. Maybe working with an AEM unit is spoiling me...
« Last Edit: February 08, 2008, 11:14:33 pm by BenFenner »
1994 Black SE-R (VEMS, going turbo)
1994 Black SE-R (with sunroof)

Offline dnb

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Re: Deceleration enrichment query
« Reply #1 on: February 09, 2008, 03:55:49 am »
There is a decel fuel cut that works reasonably well.  There is no decel enlean feature as such at the moment.

I tend to find where the car gets to in the lambda table under decel and set them to give a lambda target of 1.1 or so.  Then use the fuel cut once things have leaned out nicely.  It takes a bit of analysis to find the right bits of table, and you have to be careful that they aren't used by other areas of operation.

I too run a lambda of 1.05 during cruise.

Offline MWfire

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Re: Deceleration enrichment query
« Reply #2 on: February 09, 2008, 04:39:43 pm »
Why not lambda 1.07?
On lambda 1.07 consumption will be lowest(according to book Bosch Fuel Injection System.pdf)

Offline dnb

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Re: Deceleration enrichment query
« Reply #3 on: February 09, 2008, 10:40:24 pm »
The EGT gets a little too high for my liking on the TVR.

Offline GintsK

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Re: Deceleration enrichment query
« Reply #4 on: February 10, 2008, 01:51:44 am »
I do not like fuel cut. If right after fuel cut comes hard tip-in, there is lean condition guaranteed because of lack of fuel film.

Offline BenFenner

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Re: Deceleration enrichment query
« Reply #5 on: February 11, 2008, 09:51:33 am »
dnb, I think we're talking about two different things here. I want to give more fuel (not less) during deceleration. This is for fractions of a second of course, but this is what's typically used to smooth out lift throttle transition if I have my facts straight. From what I can tell, you're describing a smoother leaning of the mixture which might accomplish similar results (and I'm interested in your method). As of right now, I have over run fuel cut kicking in at anything above 2,000 rpms and holding until 1,400. So when I let off the throttle, I'm always cutting fuel completely and immediately.
1994 Black SE-R (VEMS, going turbo)
1994 Black SE-R (with sunroof)

Offline dnb

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Re: Deceleration enrichment query
« Reply #6 on: February 11, 2008, 05:49:17 pm »
There does need to be a delay before fuel is cut, else there is a chance of lean conditions on gear changes, which isn't good.

Correct - I was talking about leaning out on overrun.  You should be able to use my method to give an increase in fuelling too, just set the lambda target to somewhere rich instead of lean in the appropriate area so that as the load drops on over-run it passes through a rich area.

Offline Denmark

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Re: Deceleration enrichment query
« Reply #7 on: February 11, 2008, 06:59:53 pm »
Yep, that is also the thing to do on a Impreza LInkECu,

THe map area need to be rich in the low load high rpm, then you will get rid if the liftoff jerk,
I worked alot on the with the NA Toyota 4age20 blacktop , when running Open ITB´s on speed density,it was really jerke, but found that the low load rpm need to be rich, that will make the difference, you look for.


/Skassa
working on the boxer

Offline BenFenner

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Re: Deceleration enrichment query
« Reply #8 on: February 15, 2008, 10:57:04 pm »
I lowered the target lambda at the bottom of my map, and upped the VE values, and it worked like a charm. I get this nice dip in lambda when I let off, then it cuts fuel. I'm very happy with it. Thanks dnd.
« Last Edit: February 15, 2008, 11:07:59 pm by BenFenner »
1994 Black SE-R (VEMS, going turbo)
1994 Black SE-R (with sunroof)

Offline Tcal

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Re: Deceleration enrichment query
« Reply #9 on: February 16, 2008, 05:41:07 pm »
I lowered the target lambda at the bottom of my map, and upped the VE values, and it worked like a charm. I get this nice dip in lambda when I let off, then it cuts fuel. I'm very happy with it. Thanks dnd.

What´s your lambda target value in that area? I thought that i might try it too..

Offline BenFenner

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Re: Deceleration enrichment query
« Reply #10 on: February 17, 2008, 12:54:23 am »
From memory, I started in the lower left at 0.99 and subtracted 0.01 as I went right, so it looked like:

0.99  0.98  0.97  0.96  0.95  0.94  0.93  0.92  0.91  0.90  0.89  0.88 

That's about it...

The bottom row of my VE table ended up looking like this I think:

50  52  54  56  58  60  62  64  66  68  70  72

I didn't tune it or anything... Didn't feel the need to match the VE to the target lambda... I just put numbers in. =D
1994 Black SE-R (VEMS, going turbo)
1994 Black SE-R (with sunroof)