Accel enrichment

[Sleepr]

Hi. 

 

I`m having some problems getting accel fuel correct on one engine i`m doing right now. 

All other engines I have done with Link ecu, have all been working fine. But for some reason I can not get this engine to be smooth during the initial 0-whatever tps. 

It will always cough during the first movement. it`s actually so bad that looking at logs after reving out one gear and shifting to the next fast. the rpm will bounce a little indicating a engine missfire.

With the setting I found to be the closest, it will go momentary a little lean, but quite rich a short time after.   

The best settings I have found seems to be a extremely high sens ( 100 ) , with about 100-150% accel fuel ( in total from 0% tps ) and a really fast decay.

Think some of the reason for this is the nature of the engine ( higly tuned 4 cyl 2.0L turbo with quite a lot of cam overlap( mostly from a retarded exhaust cam ) , large 3.5" TB 

So 2 questions: 

Can someone ( link rep? ) give a better explanation on how the accel sens works? like how the math behind it works. 

Anyone have had this problem before, and have some settings that will work with a engine that had a lot of turbulence? 

[dx4picco]

a friend of mine had issues on a highly tuned NA 4 cyl too, and he got better results using a 3D injection timing table instead of plain single zone. Not sure what you using yet and if it would be the total answer but may be worth to take a look

[Adamw]

With accel enrichment I wouldnt put too weight on what the lambda is doing as it is not always a good indicator of combustion during an extreme transient, still use it as an indicator, but the tuning needs to be done more by "feel". But something doesnt sound right with your description to me, I dont remember needing anything like that much even with large ITB's or slide throttle engines.  The sens of 100 isnt too unusual for a large throttle or ITB's (I think I have even been higher than that) but 100-150% clamp is way more fuel than I ever remember needing..  I dont remember seeing much more than a max of around 70% from a quick stab off idle.  Typically larger overlap will mean you need less accel enrichment as there will be less vacuum at idle therefore less change in MAP during a blip.  What is the MAP at idle and what does it spike to during a blip?

Has it got some decapped injectors or long inj extensions or a completely wrong spray pattern or something?  Is it a stock kind of injector location?  Whats the manifold design like - any chance of something weird like charge robbing etc?  Whats injector timing like?  Is it direct spark or wasted spark?

 

1 hour ago, Sleepr said:

Can someone ( link rep? ) give a better explanation on how the accel sens works? like how the math behind it works. 

I dont know confidently myself but from my experience it appears to just work like a multiplier.  TPS Delta (or MAP) x Sens

 

[Sleepr]

Hi. 

Idle map is at about -20kpa, and driving can be as low as -50kpa at light loads. Initial jump is to 100kpa. ( large turbo that needs some spool time ) 

injectors is ID2000 in "stock" location. Intake manifold is a medium runner large plenum and really cant see charge robbing beeing a issue, since fuel would then have about 20cm reverse flow just to get to the plenum 

Injector timing is the normal 320-380 degrees end inj. 

Cop in full seq inj\ign 

 

Do you have a example setup for a large TB, large cam small displacement where you found it to be working good Adam? 

[Brad Burnett]

I have a lot of experience with aggressive ITB engines, and i typically find that the fuel map will have a hump just off idle to aid it smoothness and drive ability.  

[Sleepr]

I have thought about doing a alpha-n map with map comp if I can`T get this right. Should at least fix some of the issues i`m having. 
But thats last resort.... 

[Brad Burnett]

doesnt even need to be alpha n.  The same principle will apply to get more fuel in for a given load and rpm.

Shape of the fuel table will still match as pictured here for tip in area.

[Sleepr]

Adam: Do you have a setup you have found to work good on a similar setup? 

 

 

[Adamw]

Not really anything I can remember that would be hugely relevant to yours (i mostly do ITB race engines).  

If it where mine I would probably change to alpha N to see if that gives more acceptable control. Sometimes MAP (especially single throttle, big overlap) just isnt a great indicator of air flow.

Do fine breakpoints at small throttle openings like my example in this post: