VQ map histogram or auto tune

[hexdmy]

I've been using Nistune recently on several different cars, and a few things have come to my attention. Most importantly, the Maf transfer function or VQ map relationship to air flow . Tuning Nissans is fairly new to me, but efi tuning is not, and I've had experience with tuning Maf based Ford vehicles and some Subarus . In those circles, you always tune to match your commanded AFR target table, specifically, you tune your Maf voltage to flow table. On the cars that have come into the shop so far, I've only had trouble with getting commanded air fuel to match actual air fuel in situations where the car did not have the original Maf sensor, and/or the intake piping going to and from the Maf was not original, or the Maf itself was faulty or dirty. I know that any change to the routing of the Maf sensor can have a dramatic effect on the sensors calibration, especially at lower air flow. I'm interested to hear from others who have more experience with these cars, especially Matt and Pete Considering that most of the factory Nissan calibrations I've looked at have fairly smooth and linear fuel tables, I'm assuming that Nissan intended to use the fuel table as a commanded air fuel look-up , similar to Ford and Subaru, yet I see that it is generally accepted, and I myself have made changes to the fuel table to get a desired air fuel ratio .

What I propose, is to add a separate "Autoadjust" function that worked specifically with the VQ Maf table, so that the wideband value would be compared to the current commanded air fuel value in the air fuel table, and the error would be applied to the correlating VQ Maf break point. Another possibility is to add a histogram table, with the same referenced values as mentioned in the last sentence, but you would have to manually cut and paste the error, as a multiplicative into excel, or add the ability in Nistune to cut and paste by percentage from the plotted histogram directly into the VQ Maf table.

- Chris

[klattr1]

not sure if i fully understand what you're asking...but isn't the VQ map supposed to be a constant on all cars using the same mass air meter?

There was an "AFR Autotune" function in the last working Nistune version that seemed to trim the fuel table (and VE table too I believe) to sync "theoretical targeted afr's" and "real-life wideband afr's" if I remember correctly. Not sure how many people used it or if it was buggy. Are you talking about something like that or an automated feedback function that trims on the fly.

[hexdmy]

not sure if i fully understand what you're asking...but isn't the VQ map supposed to be a constant on all cars using the same mass air meter?

There was an "AFR Autotune" function in the last working Nistune version that seemed to trim the fuel table (and VE table too I believe) to sync "theoretical targeted afr's" and "real-life wideband afr's" if I remember correctly. Not sure how many people used it or if it was buggy. Are you talking about something like that or an automated feedback function that trims on the fly.

Yes, that's what I'm getting at, the MAF is not a know quantity depending on how it is installed. That is why on other MAF based cars, it is often recommended to tune the replacement MAF before any modifications are done to the car. It seems that it is assumed in the Nistune community that the MAF is a known quantity, but in my experience it is not, unless it is installed exactly as it came from the factory, i.e. original intake piping, and as the original part from the factory. On a Ford vehicle, as an example, once I calibrate the MAF curve to match the commanded air fuel table, I can put the commanded air fuel values to what ever I want, and the actual air fuel ratio will match to a reasonable degree. The same goes for Subaru and GM.

[PL]

Hey Chris,

Interesting subject. I've had PFC tuners mention this before, as it appears that this method is quite popular in PFC world. When I first heard of this I saw it as a "cheap and dirty" shortcut way of tuning, but I'm starting to come around!

My problem has always been that I see the MAF response as a standard that shouldn't be messed with. But I tend to agree with what you're saying - they do vary. Particularly at low load.

The other problem is that NIStune recognises the std VQ maps and uses this to do its calculations when changing to a different MAF. Once the VQ map is changed all bets are off. No big deal - it's easy to change K Constant and adjust load scales manually but it seems many people still rely on the automated MAF changing feature in NIStune.

One thing that I have been noticing lately is that (while tuning via fuel maps), if the map needs to be hacked around (big peaks and troughs) then there's a problem with your MAF (dirty or faulty). A good MAF almost always results in a smooth fuel map.

As for auto tuning - I'll leave that to Matt. His life is up in the air at present with moving house and all. It's looking like things will be settling down by the end of this week.

PL

[Matt]

added to enhancement list

[hexdmy]

Bump on this post, just curious if you have had a chance to make any progress with this.

[Matt]

sorry not yet. i'll escalate it

[Mads B (dk)]

anything new ?

[Matt]

Has it been four months? Sorry still on higher priority items atm

[Mads B (dk)]

News ??

[Matt]

What I've done so far is added acceleration to the VQ map (increases in 10's then 100's) to assist adjustment

I've also added some experimental code for VQ map tuning. Use the normal AFR auto tuning window and tick VQ map. It will then adjust the VQ map to reach the AFRs in this window instead of fuel map. It still requires testing and I havent had time yet (been repairing the R31 after bending the drivers door back ... when I should have been testing and tuning )