mrelia100

Specs: 2001 NB2, gt2560r, megasquirt MS3X with tune based off trubokitty - I have been running this setup for 2 years, flow force 640cc injectors, 3” exhaust.

Problem: Idle Issue: Idle rpm varies constantly with swings in AFR from 13 to 16. I recently switched from open loop to closed loop with no change in behaviour, which is frankly better than it being worse. At idle it hunts gets to 760rpm or so and shutters a bit, then swings to 1150 which can be seen in the log file below. If I turn the wheel, turn on the cabin heat, and roll the windows it dies. If it is already in the low RPM hunt, just turning the wheel could cause it to die. Occasionally it will be in equilibrium. My solution in the past was to run 1000rpm idle always, a very lazy approach.

Startup issue: - not immediately important. It often requires 2 crank cycles, or takes 3-5 seconds of cranking. I understand this takes many many tries to get right over a wide temperature range. At any temperature however, it dies if you don’t give it gas and hold the rpms a bit higher for a couple seconds. After start enrichment, taper and warmup needs work.

Solution: I believe I could learn most from someone else’s dialled in tune. Specifically my VE table idle needs work, and closed loop initial values I believe.

Not looking to be spoon-fed, lol I know this forum hates that, I really think I could learn the most from someone else’s tune, try some things out, and then ask some specific questions after that. I tried searching the forum for a good NB2 megasquirt tune someone has posted, but could not find anything. Of course many tunes posted with issues! Thanks for your consideration.

Supporting material:

Video at idle:
Log corresponding to the video, and current tune attached.

Silver NB

iTrader: (1)

I'm no expert, but I took a peek at your tune. It looks like you've modified the main spark table to be at 10 degrees in your idle area, but you also have idle advance turned on. This is by no means a "fix", but do things get better if you turn idle advance off?

I attached my tune from my car (NB1) before I sold it. It was by no means perfect, but I had finally gotten the idle close enough I wasn't going to mess with it any more.

RunninOnEmpty

iTrader: (5)

Your Idle Min Max seem way off, look like they were never set properly.

Because of this, it also impacts your ability to dial in a real Close Loop Initial Values table. You can't drop it lower even if you needed to.

When looking at your VE table in logviewer, notice how it's circling 4 cells. Try making them all the same just to see if it'll help stabilize your AFR a bit.
You can also try softening the Idle RPM Timing Correction curve (example, at -200 rpm, you have "3", try 2 or 1). If it's too aggressive and the RPMs drop below your target, it'll add too much timing and throw it into the cycle you see. I started with a TruboKitty map too, but I did alter this with a little better behavior.

fwman1

iTrader: (3)

Give this a look. Then check out this playlist by OGPedXing
https://www.youtube.com/playlist?lis...ViKBzz8iCJDRF_

curly

iTrader: (25)

First off, I'd switch to "include AFRtarget", so your fueling calculation includes your AFR target, so when you change it, fueling will change accordingly.

secondly, your idle advance isn't really doing much. I'd disable idle advance and turning RPM timing correction instead. I add 10 degrees 100rpm below target, subtract 10 degrees 100rpm above. This way ignition advance flies all over the place when active, but RPM remains stable. As others have said, I'd increase idle timing to closer to 14-18, and make sure if your RPM does dip below your idle column, timing increases there as well. Then target all your RPM columns to make sure fueling in them is correct, so if idle does hunt, it doesn't start to lean out. Once full warm, set idle valve test mode to 0%, and make sure you can still idle around 100-150rpm below your target. If it doesn't, you'll be trying to compensate for not enough bypass, and have a lot of stalling issues. Then slowly increase idle DC in test mode till RPM starts to rise, that's your minimum. Then keep going till it stops, that's your max. Then turn on CL idle, see what it duty cycle it settles at. Set your initial value in your target column to this figure plus a few points. Then blip the throttle, it should return to your target RPM or a little high. If it dips low, add a few points to the initial value table and try again.

I might have missed a few steps in this process, but it should get you started.

Ted75zcar

iTrader: (2)

Good rundown Curly, the only thing I would add is to do the initial values test with accessories (AC, cooling fans, heater blower, headlights) on.

curly

iTrader: (25)

Sure, although I’d remove AC from that list and make sure it works well with the idle up feature, which should target a higher idle, therefore
A different initial value column.

if you target a idle return of ~+100rpm above target, that plus the idle advance settings I suggested should compensate for any other loads.

HowPrayGame

Throwing in my tune, my Idle was near perfect for a naturally aspirated car. A very similar set of idle settings on a 91 NA Supercharged idled near perfect with similar timing control mechanisms and PID values. Closed loop idle initial value tables are per car so work on that.

Thank you Curly for your idle settings, that's where most of my idle control tables came from across various threads when I put it all together.

Make sure your VVT isn't activating during idle, it will **** everything up and make it impossible to tune. My VVT settings are made specifically to kick in at 1600 rpm so it never occurs.

TUNE IS FOR A NATURALLY ASPIRATED CAR DO NOT COPY THE FUEL AND SPARK TABLES IF YOUR CAR HAS A TURBO OR SUPERCHARGER