Erm ?? Vishnu ?

[Mortster]

Found this while searching for a MAF..



Introduction

If you have just reset your ECU or reflashed it with a new map you may know that this also resets your ECU learning data. Below is a little trick I found on a Subaru forum that has been shown to accelerate the factory ECU’s ignition timing learning process. This procedure is commonly known as the Vishnu Reset after the company, Vishnu Performance, that wrote this on a Subaru forum.

Background

There is something called Ignition Advance Multiplier (IAM). It represents, by some complicated algorithm, the average learned positive knock correction applied to the ignition maps. It’s represented in 1/8th degrees increments. 1 being the lowest and 16 being the highest (1/8 to 2 degrees in absolute terms).
The “happier” (knock free) the car is, the higher the number will be. Conversely, the lower it is, the more knock prone it is. This number, after ECU reset or ECU swap defaults to 8 and usually creeps up to 16 (if well mapped) through normal driving. Depending on driving characteristics, this can happen within a few hours or a few weeks. Well, here’s a way to make it happen in about 5 seconds ….

Fast learning procedure (Newage WRX)

1. With the car fully warmed up, reset the ECU.
2. Drive to a nice open road without traffic. Don’t go on boost until you get there. Put the car into gear (3rd gear works the best) bring the revs up to 2600rpm.
3. Push the accelerator pedal down slightly so boost stays around 2–4psi (~0.2 bar). You will need to MAINTAIN 2500rpm and 2–5psi for approx 5 seconds. You can do this by left-foot braking gently as to prevent acceleration. During these few seconds, the advance multiplier (which you can’t see so you’ll have to trust me) will go from 8, to 12 and then to 16. Works like a charm. And on our reset or reflashed ECU, is worth an immediate 10–20 BHP.

Fast learning procedure (Newage STi)

The procedure is slightly different for STi’s.

1. First you have to reset the ECU.
2. Then let the car idle until it is fully warmed up in closed loop fuel control.
3. Then hold approx 4–5psi (0.3 bar) of boost at 3500rpm for 3–4 seconds. Again left-foot braking will help you maintain a constant speed. This usually results in a increase of 20 BHP. This is something that you would probably see eventually over the course of a few days of driving. But this takes a few seconds and is great for those who are dyno testing/tuning or are just really impatient

Warning: This little trick artificially speeds up the learning process. This is only a good thing if the re-mapped ECU is mapped properly. If there are trouble-spots where knock is present, this trick will make it even more present. So be careful!

Erm??? Bless You




Gonna try it then?

[Mortster]

Need to get some port software on the laptop first, then a usb-obd lead. Anyone else even heard of this? Or is it Bull?

[Scott.T]

When you first reset the ECU the IAM is set to 8 (unless it's been remapped and the Initial IAM is set higher).
This gives you half the advance timing map.

The ECU has a base timing map and an advance timing map.
The base timing map is the least amount of timing the car will run for example at full boost 4500rpm timing may be 20 Degrees.

On top of this is the advance timing map which will give ou for example an additional 8 degree's.

With an IAM of 8, you will only get 4 of the possible 8 degree's therefore giving you 24 Degree's of timing.

you still with me.........

With an IAM of 16, you will get 8 of the possible 8 degree's therefore giving you the maximum possible 28 Degree's of timing.

With an IAM of 2 you will get only 2 degree's so 22 in total. 'BUT' with the IAM this low the ECU will also limit the boost to about half and put it into a kinda limp/safe mode.

The learning procedure above is kinda OK but the 2001> ECU tend to learn fairly quickly and a couple of spirited full throttle 3rd gear pulls and a couple of 1/2 throttle pulls will increase the IAM from 8.

But if the IAM was higher then 8 before the reset all you will do is retard the timing then advance it back to where it was.

Also, if for whatever reason i.e poor fuel, a problem or anything that can cause a slight bit of det, the ECU will just pull the timing again.

Unless you have put the wrong fuel in, the ECU will sort itself out.

i.e it can pull timing, but can also put it back in again.

This is what makes the difference when you put V-power or Tesco 99 RON in the car.
If the IAM has reduced to say 12 on 97RON, you are not running the maximum available mapped timing.
If you then put V-power or 99RON in the timing may advance back to an IAM of 16, therefore giving you a tad more power.

However if the IAM is already 16, then adding V-power/99RON will not cause any timing adjustment and therefore you may not feel any difference.

[Jolly Green Monster]

there is even a fine learn on top of that..

no point doing it as Scott says the ecus monitor and play with timing continually.. so just resetting it and making it relearn will gain you nothing.

Simon