Fuel cut?

[manselainen]

Maybe I somehow managed to get my first overboost protection fuel cut today, see attached log (30122011 17) at 60 secs.

4822 rpm
MAP 231 kPa
baro maybe 99 kPa

EU 98 hiload tune (not modified that part, tune is also attached).

What's a little strange to me is that I didn't see any overboost protection throttle reduction, due at MAP 229. That should have kicked in.

I interpolated boost cut limit to that operating point from existing table and it's pretty close to 231 kPa so that's probably what happened. Or is it yet something else?

I think I'll increase overboost protection fuel cut limits on row baro 93,51 by 5%.

Steve & co. any comments?


By the way, why can't you attach .vtune files as such? They are small anyway...

[Steve @ VersaTune]

The actual AFR does not indicate any fuel cut. It does not look like an overboost fuel cut event.

There is a timer involved. The ECU has to see excessive boost for a period of time before it starts to act.

What gear were you in, and is there a possibility that you lost traction?

[manselainen]

I've never had a fuel cut so don't know how it should look in logs...

Anyway I know for sure that it was on 4th gear, no traction loss, sudden loss of all power, almost banging my head to windshield so to say, not like when hitting rev limiter.

MAP was 231 and interpolated from overboost protection fuel cut table (rows baro 93,51 and 101,4, RPM's 4500 and 5000) I get interlocking limit of 231,26...

These values in said table:
________4500_______5000
93,51___217,2507____216,1336
101,4___239,4471____236,7574

Operating point: baro 99, rpm 4822
calc, calc, calc -> 231,26

But there was not much time for any timer... what the hell happened?

[Steve @ VersaTune]

Sounds like a fuel cut. It scares the hell out of ya doesn't it? Did you lift the accelerator pedal immediately and coast for a bit? I don't see a dip in the logs. I just see what looks like a lift of the accelerator pedal.

Usually when there is a fuel cut, you see the actual AFR jump to 29.99 or 2 lambda or so.

[manselainen]

I lifted the pedal immediately and was happy to notice engine still working
Kind of scary event though.

Thanks again Steve.


Maybe there's a timer in throttle reduction part as it did not react at all?

[Steve @ VersaTune]

Based on my experience, there is a timer for both. It's possible that it happened so fast that the timer expired for both at the same time.

Try putting a little more kPa between them since your engine spools pretty quick.

[manselainen]

Diplomatically said...

I think I'll up the fuel cut limit and don't drop the throttle limit. No limits FTW (or not)