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Idle problems

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I'm from brazil and I work in EESC USP Formula SAE Team, our engine is a KTM 375cc, from duke/RC390, it runs on E97 fuel with 19mm restrictor in intake and 3.8L plenum (the throttle body/restrictor is placed before plenum), fuel is supplied by a bosch EV14 injector (0280158123) and controlled by a fueltech ft600 ECU (sequential injection and ignition). This year I had many problems to configure a stabilized idle and I would to know if the plenum is the main reason to this. I'm attaching a .CSV log file.

Attached Files

I checked your log and basically everything is surging up and down.

How is idle air controlled on the engine? Does it have a cable throttle with an idle air control valve, a cable throttle with no idle air control valve, or electronic throttle? Have you checked for vacuum leaks by spraying carburetor cleaner around the engine?

What feedback systems are you running in the ECU? The oscillation looks like a control loop is overshooting but it could also be you jumping back and forth between cells in your fuel map (getting too lean, too rich, too lean, too rich). Either the idle air control loop, the closed loop lambda control loop, maybe an idle spark control loop could also be running and the gains are set too high or the target can't be achieved.

You need to temporarily run everything in a fixed state and see if you can stabilize it. Set the whole spark table to a fixed setting (say 15 degrees). Set the injection time to a fixed value (say 2.9). Set the idle air control duty to a fixed setting if that has a map or a feedback loop (set it to like 40%).

G'day Victor.

I'm going to assume you're running a cable throttle, and no form of electronic idle control, as I don't believe the FSAE rules allow for such... They didn't when I was involved anyhow.

Ray has a really good point about your ignition table, as I can see your ignition advance bouncing around a whole lot. I'd flatten out the table where the engine idles and see how it responds.

The year I was involved with FSAE, our car was a 450cc single cylinder turbocharged engine. We experimented with plenum volumes, and found that anything over about 1.5L would cause an unacceptable lag between throttle position and engine response. Your plenum volume of 3.8L on a 375cc engine is probably great for the maximum power you're seeing, but I think your drivers will complain about the car pushing into corners after they have released the throttle, and being sluggish to respond on the way out.

Prove me wrong though, that's what FSAE is all about! :-).

Having a look at your logs graphically, are you using ignition advance to try and control the idle?

Have you tried running the engine without the plenum?

For sure you've got a massive oscillation the ecu is constantly chasing its tail trying to stabilise.

Always stay on the left hand side of the plane! ;-).

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Thank you for help Raymond and Zac. I'll try to use a fixed ignition timing on idle areas and see what happens. The engine hasn't any kind of idle control. The car pushes a little into the corners but throttle response is very good. What kind of engine did you use, Zac?

A Husqvarna 450CC dirt bike single. One thing that helped a lot was having a much more conservative custom cam machined. We couldn't use the engine effectively in the high RPM zones due to the restrictor, so we shifted peak torque down to a lower rpm point, to give us more overall power and a wider usable powerband.

Just had a quick look at your log again, what are you using for your load axis input on your fueling table?

Very nice Zac. We are considering using a turbo in the near future.I'm attaching a pic of our actual ignition map.

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Can you post up a picture of your fuel map too?

For sure, there it is

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