rich11010

Hi all,

First post on here - have been trying to learn this tuning lark by doing. But it turns out its pretty tricky, and I could really do with some pointers!

Setup is a 1999 MX-5 NB 1.8 - with S/C and MS2v3. Base tune was provided with MS and was more or less fine. I have sorted out some minor things, but there are a couple of issues which I have been round in circles several times, without being able to truly fix. I thought I'd start with the most problematic...idle oscillation.

Following a 'blip' of the throttle at idle, or during gear change) the RPM undershoots the target - down to ~500rpm, almost stalling before recovering. Usually the oscillations decay after 4 or 5 cycles - but sometimes it carries on for a while.

My understanding is that the rpm should fall and become steady at or above the target before CL idle engages - which is what is not happening. It is the CL idle which is catching the falling rpm and pulling it back up - so I don't believe it is a problem with any of the idle settings - though I do need to (re-) tweak them from where I am today.

I have played with fuel and ignition in the regions before and during the undershoot, and after it (at idle). No luck.
I previously had the issue masked with an high dashpot adder - but that led to other problems.

Attached is the tune and a couple of logs showing typical examples
In "log01" there are many "blips" at idle. I was changing the fuelling slightly during this log, but the behaviour is pretty constant.
At the end of "log02" there is much oscillation following low-speed maneuvering.


Could some of you tuning gurus mind having a look over these and let me know the schoolboy errors you see? Any help much appreciated.


Rich

Braineack

iTrader: (62)

upgrade to gslender code with a/c input.

rich11010

Thanks - I will check that out.
As I don't have a/c though, and in all the cases I've seen this oscillation the load has been constant, is this behaviour expected without the improved code?

Braineack

iTrader: (62)

Still has awesome idle improvements to merit the switch in firmware.

andrew

Do you run a intercooler with long pipe route from the charger to the inlet? I understand it as follows, The long route leaves a lot of air inbetween the charger and the inlet plenum this is what causes the osilation. Installing dual throttle bodies one before the charger and linked by a cable the the OEM so that they operate in parallel is a way of solving it.

To prove, install the following setup temporarilly to test. air filer to short inlet pipe to inlet temp sensr to OEM throttle body. If this setup stops the osilation it not a MS setting. Its a mechanical issue.

Note: take belt off charger, if its not connected to the engine is VERY loud

JasonC SBB

There was a huge thread started by "ggermar" who had the same idle issues on his s/c setup, which ended up with gslender coding in huge improvements .

rich11010

Thanks for the replies so far!

Have updated to the latest gslender code. I'd say that it is slightly more stable. However, I have not managed much tweaking as I have had confusion due to "Table Switching" becoming active following the firmware update, and it using the alternate tables for both fuel and advance. (Took me longer to work out than it should have!)
I don't understand enough about how it picks which table to be certain, but this could explain a lot about my previous issues finding that changing the advance table had no effect...

Andrew - no intercooler, so between the charger and the inlet there is the "stock" length of pipe. But I have the idle control valve right at the inlet on a dummy throttle body, so I don't think it can be the situation you describe. It does remind me that if/when I upgrade next and add intercooler, this issue may rear its head...did you have this at some point?

Jason - This is what I was hoping for...in fact I did find that thread in a search the other day. As you say, it was quite long...[guilty face]. Will go back and read in full.

Will post again once I sort out my table issues - hopefully the gslender magic will work!


Rich

andrew

I installed the intercooler with the charger. I still have it sometimes. I must try adjust the idle speed on the throttle body. I havn't trued the Gslender code yet either. Mine only happens if I get off the throotle quickly and put he car in nuetral. I drops to 500 and then creeps back up to target where it stays.

rich11010

No, no, no. Wrong. What I missed here is that the IAC valve lets air in downstream of the throttle. It doesn't matter whether it is located right at the inlet, or over by the charger outlet - it's still having to alter the pressure of the throttles volume to make a difference in the idle speed - and therefore introduces lag, as Andrew rightly says. And as Jason says in Greg's thread which I am now properly reading...

BUT the problem I'm seeing is with undershoot in idle speed before CL kicks in. Therefore I think just to do with spark tune. And maybe AFR as rpm falls?


Rich