What is digi-lag?

[leew 0]

Can anybody tell what digi-lag actually is. I've looked on the SNS web-site and it states -

 

Whats new? Our stage 5 chip now has NO DIGIFANT LAG. Ever wonder why your air fuel stutters and so does your car for 0-3 seconds?

 

Why???

[GazzaG60 0]

digi lag is not physical lag as in turbo lag it is lag within the injection system and is effectively the time it takes for the system to go WOT and fuel accordingly. on a gauge it kinda flutters about when it should be holding. kinda cant make up its mind what is going on. ive seen a SNS no lag n it just goes n holds real time as it should

[leew 0]

I thought WOT was activated by a switch on the throttle. Why would there be a delay. Isn't it just on or off?

[Jon TDI 0]

The ECU takes time to read the signal from the WOT switch. The SNS chips over-ride this signal & immediately richens up the mixture.

[leew 0]

Don't chips just contain look-up tables for fueling under different conditions eg. idle, WOT, certain loads???

[Dubcharged 0]

At times like this i wish I had my site ready :(

 

OK, Digi-Lag is an inherent feature/fault in the Digi-1 and digi-2 ECU's, ie G60 and Polo G40. I'm currently testing to see if my digi 8v gti does it too.

 

Under normal driving, the ecu reads off the lambda and trims the fuel to keep the average at 14.7:1 (stoichiometric). In real time with an A/F gauge you can see this as the A/F cycles up and down where the ECU is working to trim the fuel. This is closed loop mode.

 

When you floor it (WOT) you do hit the full throttle switch BUT the ecu continues to cycle the mixture for a second or so (not always the same time) before it hits the map value. So enrichment is "lagged" and this happens again as soon as you take your foot off, change gear and floor it again! :?

 

So you can imagine the effect this has: You're coasting along, a Type R comes up beside you, you drop a gear and FLOOR IT, boost shoots to 1 bar (68 pulley) BUT your fuelling is cycling still :shock: SO under full boost your fuelling is going as lean as 16:1, sometimes worse :shock: So your initial throttle response is letting you down and the Type R edges away, a second or so later your enrichment kicks in and the car starts to gain on the Type R :twisted: Now you gotta change gear, you do so and the bullshit lag kicks in again :oops:

 

Its not just under WOT that we've eliminated Digi-Lag, you all know that under 70-80% throttle, you can build good boost. Here your ECU is cycling still BUT we've mapped it so under normal driving, if you get boost (8psi) then the ecu will stop cycling and giv your poor pistons the fuelling.

 

I can talk about it all day, but you have to really try it for yourself to see the difference in response, not to mention the safety factor of lean out under boost which has been eliminated. :D

 

Phew (By the way, this code has been copyrighted under international law)

[leew 0]

I have found some lit that might explain the delay. Its quite interesting a brings the carbon canister into play :?

 

At full load there is a pressure difference for the carbon canister between, ambient and the pressure in the hose before the supercharger.

 

With this the canister is also scavenging at full load. In the transition from normal scavanging range into full load there' is a difference in the scavenging rate. To compensate, for this, the lambda closed-loop control is not instantly deactivated in the transition to full load (WOT), but instead control continues for a brief period dependant on engine speed.

 

So would removing the carbon canister stop the pressure difference and thus allow the ECU to go into open loop instantly without the lag???

[Dubcharged 0]

You'll find that the Digi-Lag remains with the canister removed. Interesting theory though! :D

 

Neil (Volkspeed) is doing a 20v engine with the G60 ECu as control brain. He gets digi-lag! No carbon canister there! Its not the engine, its the ECU.

 

VW put this into the ECU on purpose to improve emission/mpg. My 8v GTi has it too. For stock boosted motors this lag isn't much of a problem since at low boost level, lean out doesn't do too much. However, when you go 68mm or smaller, it becomes much more substantial since boost build up is quicker. Digi Lag is based on a time domain, it doesnt see how quick you build boost, it just lags at a preset period regardless. :?

 

With our map you can actually remove the WOT switch and fuelling will still work fine! So people with old and perishing WOT switches need not worry. We actually advise this for turbo set ups since it'll make the turbo spool up 500rpm quicker. :D

[leew 0]

No WOT switch :shock:

 

Have you mapped the chip to run on the air flow sensor input alone?

[Dubcharged 0]

nope, its a lot more unique than that. Obviously I cant go into detail about it but what i can say is that our maps aren't your normal chips tweaked from stock!

 

:D 8) :D

[leew 0]

Ohhh go on...its just gett'in interesting :)

[GazzaG60 0]

WOT override to help prevent problems with reaching lots of boost, which you can happen with smaller pullies even not at full throttle?

[leew 0]

How???

[GazzaG60 0]

magic trickery.

 

tell the brain that when a certain boost level is reached to go WOT and use the maps that have been adjusted/rewritten for those settings.

[leew 0]

Ahhhh so thats how you have got over the delay, because you don't use the WOT switch.

 

As i said in the earlier post (a section from VW devopment documentation of the digifant system) when you hit the WOT switch there is a difference in pressures, to rectify the differences the digifant system keeps the close loop for a certain period. Because you don't use the WOT switch there is no need for the closed loop to be kept. Hense no delay.

 

Am i getting close :D

[Dubcharged 0]

LOL :lol: Leew, the ecu doesn't necessarily rely on the WOT switch to switch to map value, it will go to map value after a preset boost level anyway (hence the vac/boost line from throttle body to ecu) We've brought this value lower. As soon as you tell the ecu (WOT switch or boost level) to go to map value, it will have the lag regardless. Like I said this was programmed by VW.

 

We brought out the WOT feature AFTER the gen 1 No Lag code. :wink:

 

We still use closed loop mode, you have to otherwise driveability and economy would be terrible!

 

The No Lag feature isn't a simple piece of code or instruction, its integrated into the map as a whole.

 

All you need to know is that it works flawlessly and its great :D

 

C'mon, stop torturing yourself and just try it out! :)

[leew 0]

Maybe i like pain :D :D :D

 

Sh*t, i thought i had it then :D :D :D

[GazzaG60 0]

id have said that the code has been optimized and reshaped to remove the digilag. it must still cycle in order to attain optimum runnig for fuel and emmissions purposes. however if didglag is a bosch pre-deturmined process and not a inherent problem then it can be removed by code tweaking.

 

maybe the lag is there so that each data sender can finish cycle, i dont know this is speculation. the brain is obviously trying to deturmine what is required and this probly varies from country to country and year to year. with a preset config like the SNS ie 68, red tops, 268 cam, 3.5bar FPR then the setup is going to be v similar everytime. similar boost, timing fueling requirements. the programmers-danny, sam, bilal,???? know roughly what will happen and so can drop the WOT switch as they know WOT boost can be done prior to WOT if you get what i mean.

 

it obviosly aint as simple as this and lots n lots of development has gone in along with testing to get what we can have today.

 

im probly miles off whats going on really but it keeps the thought process running.

 

once this sack of turd is running proply ill have one as ive seen it n felt it n it was good nice power..

 

deep breath..........

[Dubcharged 0]

I love you guys!! :D

 

Gazza: Even if you tell the ecu to go to map before WOT switch engages, it will still lag!

 

I understand fully that you guys want to know how its been done. However i'm sure you can understand my position too. Since we're the ONLY people to have developed G60 maps to this stage and removed Lag, its something that many other tuners are itching to copy! :x

 

C'mon guys, give me a break and just enjoy the fruits of our labour! :D :D

[Chris VR6nos 0]

Mmnnn......Interesting.

Have you done anything with the VR Dubcharged?

[Dubcharged 0]

Chris: We're working on some maps for the supercharged VR6. Also on the standard Vr6 lump although not sure if that'll be worth doing yet since not much can be gained with a chip alone.

[GazzaG60 0]

ok fair game.

 

got to admire our persistance for knowledge :)

[leew 0]

I'm sure we can wear him down if we keep at it :wink:

[Chris VR6nos 0]

Watch this space then! interesting!

[G60 0]

i'm plannin a trip to kompressor kanada (sooner than i thought :cry: ).. can dave do a custom map for me right there?