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Weird puttering on idle coming from pulse width randomly doubling

Practical Standalone Tuning

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Hey all,

Like the title states, Idle is holding around 900 RPM but PW1 is randomly spiking from 1.7ms to 3.4+ causing a sudden rich mixture. This doesn't make the idle terrible but a little rough. The AFRs are also struggling to stay stable when this happens too. Just curious if anyone knows a cause to this symptom or what I should check? Injectors are ID650s in a Miata with a VVT swap. I can post the tune and logs as well but here is a video of what I am talking about.

https://www.youtube.com/watch?v=X1h2Z6dv-Ts

Let me know if there are any other questions that could lead to me solving this.

Thanks a ton!

Collin,

Lots of things can cause erratic IPW, but here's a handful of items I'd start with.

I'd review all sensors to see if any of them are unstable, especially MAP, baro, TPS, fuel pressure (if fitted) but also temp sensors and anything else that impacts fueling.

I'd check battery voltage in case it varies where this occurs.

I'd check for triggering errors, odd RPM trace behavior.

I'd verify whether idle mode is enabling/disabling when this occurs.

Hey Mike,

Thanks a ton for this input. I did see on a Miata forum that disabling Acceleration Enrichment would be a good place to start. I will look at everything you have sent as well. The thing I have been focusing on is why only one set of injectors are doing this and not the other. I'll come back with news once I have tested!

Again, thanks a ton for the response!

You're welcome. If one set of injectors is doing this and another is not, are they different injector models?

Perhaps check settings related to minimum injector pulsewidth, dead time, and low pulsewidth compensation for non linearity.

Hey all, update!

I am about to go out and do more testing but I had some thoughts and info to add.

The 4 injectors in the engine right now are all ID650s. I do have other injectors I could try.

All the injector settings look good for linearity as well.

Here is a log of the idle as well.

Attached Files

For the PW doubling on idle, your log shows that the Accel PW is active during that time. That is because your TPSdot (Tps rate of change, in %/sec) is exceeding the threshold to were to start adding ms to your base pulse width. If you look at the bottom graph in the picture attached, you'll see some small red spikes which represent the added pulse caused by the accel enrichment. The white line represent the TPSdot and you can see some small ripple.

Another thing to note is that depending on your Megasquirt model, the inverse of the TPSdot threshold (the rate you close the throttle) will be used for the decel cut.

You'll need to raise the threshold of the accel TPSdot in order to prevent this happening!

Hope it helps,

Frank

Attached Files

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I turned enrichment to time-based instead of accel-pump and it solved the issue! Now to dial in the heatsoak and cold start idle issues!

I know tuning the accel-pump is what I will do in the future but I am happy to have a dead steady idle at 850. I have never had that before on my own tuning.

Thanks a ton everyone!

Attached Files
  • 2023-08-10-08_26_07-TunerStudio-MS-Ultra-v3.1.08-AutoX-Hunter-MS3-1.5.1-release-20171006-16_.png
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

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