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Idle throttle blipping causing random misfires

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Hi All,

Got a really weird problem at the moment. Have tuned a turbo charged BRZ. Currently running on 98.

When blipping the throttle really quickly about 10 times or so (taking off or idling), the car is misfiring on random cylinders. I have ruled out the fact this is hardware related as I have another base map that does not do this. Misfires are random and I cannot figure out why. It never happens under load or when driving hard. Initially thought it was the ignition timing being too retarded. And then I moved to thinking that the car is running rich down low. Sometimes I see a fuel trim correction of around -10%, or more when blipping.

Any help would be much appreciated. I've attached 2 logs and you can see from the roughness monitors that there are misfires when I'm quickly blipping the throttle. I've tried making the fuel trims (via maf scaling leaner) but it doesn't seem to help much.

Cheers.

Attached Files
  • ZA1JD00G-racerom-v1.88-05-07-2020-15-09-12.csv
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

  • ZA1JD00G-racerom-v1.89-05-07-2020-15-38-37.csv
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

When an engine accelerates rapidly (like when you free-rev by blipping the throttle), it can be challenging for the ECU to initiate the necessary charge time for the coil early enough to fire, as the engine is still accelerating (in other words, it thinks it has 3 ms, but the engine is accelerating, so there is only 1.5 ms that goes by before the crank angle needs to fire the spark. Insufficient coil energy = misfire.

Can you compare your two maps and see if the dwell is different?

One other thought -- do you have have DFCO (decel fuel cut off) active on both maps?

The other base map is locked. I cannot see the dwell times unfortunately. Doesn't look like this is something that can be logged either.

I have not adjusted the dwell time. Using the stock map. What you say makes sense and this may be the issue. But I am a bit concerned with adjusting the dwell time. I would have thought factory settings would be okay. Even with a turbo.

The DFCO also seems to be enabled. Overrun fueling should also kick in below below 1300 rpm. I tried disabling all overrun fueling below 1300rpm to test... but still got random misfires.

What air metering method are you using? It is most likely down to the interaction between the throttle opening, the volume of the charge cooler, the plenum, the injector response to the demenad, and the actual air-fuel ratio all those variables actually give you.

Using MAF scaling. I do see the wideband dip into the 11's when blipping quickly. This is what made me initially think it is a rich misfire.