MAF change in Nistune

[MrStabby]

MAF change in Nistune

Warning: Noob hackery

I have swapped out stock MAFs for Nismo MAFs, then used the Nistune Change MAF function to update from BNR32 RB26DETT (290 HP) to Z32 VG30DETT (500 HP). This causes a slight change in profile of the VQ map and changes K from 233 to 401, which is same ratio as 290 to 500. If I now try to start the car its too lean (leaner than my WB can read). As an ugly hack to get it to idle, i changed K from 401 to 880, and it idled at 17:1 and if i take it to 1100 it idles at 14:1. If I then drive its really rich off idle eg 10:1 as would be expected. Now i want to see if normal driving is ok at K=401, so i need to richen up the idle. I've changed the bottom left cells of the fuel map (all originally around 0). I tried 3, 6, 12, 24, 48, uploading the maps to ECU after each change, but the idle stays way too rich.

No idea where to go from here...

[GTSBoy]

It doesn't idle on the main fuel map.  If TPS is closed then it's running off the idle fuelling stuff.  That's why it doesn't respond much to fiddling with the lower left cells at idle.

The change AFM function has always been a bit horrible.  To make things worse, newer versions of Nistune (software and firmware both required I think) now use a concept of a total injection multiplier instead of changing K so you don't have to rescale the axes on the maps.  So it has all become a bit more confusing.  It might be worthwhile working out where your board and software is with regard to these changes and make sure that you're using the tuning guide/instructions appropriate for the era.

cheers

[MrStabby]

My board is a very early one and has not been sent back for the newer firmware. No feature pack, and I'm using the latest software v1.2.62. What's the idle fuelling stuff called in Nistune?

EDIT: Also, if I use the accelerator, only pumping adds enough fuel to keep the engine running, if i just hold the pedal down a bit it still goes too lean and stops

EDIT2: Found this in the workshop guide "Adjust latency to trim idle/low load mixtures (there is no separate idle mixture table in Nissan ECUs)"

[GTSBoy]

Actually, I probably cocked up about the idle fuelling.  I was thinking of the crank enrich table which is used at cranking and for a very short time after cranking.  Not idle.

The fact that you have had to more or less double the K value after the change suggests that perhaps you needed to check one of the halve/double check boxes in the resize AFM dialogue box.  I haven't ever done it on a twin AFM engine, so have no direct experience.  Worth a try?  The documentation (the workshop tuning notes) kinda makes it sound only like this is needed when using singles onto a 26 or a GTR AFM onto some other car.  But maybe I'm misreading that too.

[MrStabby]

Yeah i had a thread on the Nistune forums about those settings because i thought the same thing;

http://forum.nistune.com/viewtopic.php?f=8&t=3402

I'm still not sure what to do based on that thread, and perhaps the original tune was done with incorrect settings, which will further confuse the issue. I guess i'll just stuff around with the halve/double stuff to see what gets it somewhere close, then play with K and injector latency to get it it the right ballpark before it goes in for more boost and dyno tune.

[VFRegal]

Read the manual/guide. If you are just changing maf then there is no need to touch the maps. Plus as idle (if like the sr20) they are in closed loop, so you have to disable that first.

Normally idle afr's are adjusted with the injector latency. As GTSBoy said, I think your issue is more to do with not choosing the half / double box.

 

[MagicMikeZ32]

Silly question, how sure are you that a 'nismo' maf = Z32 maf?

[GTSBoy]

The intention of the Nismo AFMs for RB26 was that they had the same airflow-voltage characteristic as Z32, just in the original sized smaller housing.

People wrongly interpret that to mean that they have Z32 internals in RB26 housing, which is not the case, because that would give stupid results.  But it helps people to think of it that way.

Anyway, unless there's something wrong with the AFMs they should have a VQ curve almost identical to Z32.  It's what they were supposed to do.

[MrStabby]

21 hours ago, GTSBoy said:

The intention of the Nismo AFMs for RB26 was that they had the same airflow-voltage characteristic as Z32, just in the original sized smaller housing.

People wrongly interpret that to mean that they have Z32 internals in RB26 housing, which is not the case, because that would give stupid results.  But it helps people to think of it that way.

Ah - of course that makes sense, but i'd completely missed it. The flow characteristic matching is very close (the 22680-RR580 is the Nismo). Anyway, i've fiddled the K and injector latency so its fine to drive, and booked it in for a dyno tune.