Nistune Forums

I am tuning an sr20det (82f03) in a UK s14a.
The car was already fitted with z32 and yellow 555cc injectors. I have done the usual changes for injectors and MAF and adjusted K constant. I have also adjusted the latency (have this same problem with latency values of 580, 610 or 710).

The issue I have is that after revving the engine it will return to idle mostly as normal. If it is revved higher it will more often than not return to idle then stutter a little and die out completely. I have attached a log of this happening. The idle AFRs in the log are very slightly on the lean side but this happens regardless of the idle AFRs as I have tried richening the mixture.

What I notice is that when the engine stumbles, the load in the fuel map jumps to higher load columns and flickers a little as the engine stumbles and dies. The jump in TP can be seen in the log at 58.5seconds. I have adjusted every parameter I can see that relates to AFM and idle stabilization and none have made a difference.
You will see in the log the engine is revved a few times and it stalls after the last attempt. You can also see the rpm pick up slightly towards its 900rpm target just before dropping off. Also notice that on the first very light rev the idle returns as it should to around 1200rpm initially before gently returning to its target. When the engine is revved higher this doesn't happen at all. It simply drops straight to target and overshoots it a little. Again, I have tried adjusting for this but nothing seems to make a difference.

Unfortunately consult won't show me what the Idle valve is doing so I have no idea if that is the cause. The only thing I can see is the TP value jumps from around 1600 to almost 5000 just as the engine dies. This can be seen live when monitoring the fuel map trace and this happens every time the engine dies.

Could possibly be a bad MAF but the behaviour of the raw MAF value in the log doesn't match the strange jump in TP.

Does anyone have any idea as the why the TP value would jump up like that?

Just to add.... I have also witnessed the engine simply stall on it's own while idling for a minute or two without me changing or touching anything at all. It simply idles perfectly one second then dies instantly. Although I haven't been able to capture this in a log yet, I have noticed the fuel map trace jumping to higher load in the same manor.

Searching unfortunately didn't show anything just quite the same as this issue.

Many thanks,
Gav.

TP = MAF / RPM * K constant effectively

Where you see a spike in TP is when RPM drops, but MAF voltage is still high

I've covered this in our MAF tuning document here now:
http://nistune.com/docs/Nistune%20MAF%2 ... 0Notes.pdf

Increase your TTPmin and reduce TTPmax to reduce where you get a spike in TP

Thanks Matt.
I had maxed out my TTPmax temporarily for tuning purposes. I had assumed this table was only referenced during acceleration.

That's great I'll give that a try.

yes, its also works for acceleration. I want to say, that if you lower to much, you will get lean on accel.
The same thing is to log in which cells it floods (injector duty raises on decel) (it will be something around 800-1600rpm with 20-40 TP), so you can lean high TP cells, but make sure you wont get in these cells on accel, because you WILL get in these cells, for example in 20-25TP, but maybe not 30-40 (so this is the place you can lean and sometimes this will help).

Yeah the engine fuel cuts on deceleration as normal and then goes very rich as it drops to and just below idle target. Usually this alone isn't enough to stall the engine ad the rpm picks up again to idle. It is at this point the TP jumps to the higher load areas. Should be simple enough to reduce the TTPmax around these areas to reasonable values to help the problem.
The main issue is the very bottom rpm row (800rpm) .

Thanks again for the help.

gsportcars wrote:Usually this alone isn't enough to stall the engine ad the rpm picks up again to idle. It is at this point the TP jumps to the higher load areas. Should be simple enough to reduce the TTPmax around these areas to reasonable values to help the problem.
The main issue is the very bottom rpm row (800rpm)

only TPmax setting wont help. I will try to explain:
TPmax limits TP at given RPM, but not at given TP load, while leaning cells gives you lean spot at given rpm AND at given TP load. So, this means, that if you will limit TPmax for all 800rpm row, you cant make it zero because on accel you are still in 800rpm row and hitting for example 20-25 TP load, right? Hard to explain, so maybe my photoshop skills will help here:

How far did your AFM away from your turbo compressor inlet ? And what BOV does it have ?