how to enable the overrun fuelcut......

[rossi46numberone]

Hi,
I have some difficulty to make the overrun fuelcut working properly.
I would like to make it work with the idle thorttle thershold and RPM and not with KPa.
When I try with Kpa the the car is undriveable at low speed/load and the engine drop brutaly to idle and sometimes dies.
In fact when I press slowly the thorttle I've got a bad on/off sensation :-(.
At this time I'm running without overrun and no issue;the engine slowdown very smoothly....
What would the best compromise to keep this running way and make fuel economy and full decelaration engine braking force.
Did I forget something in Vemstune????
Michele

[mattias]

It's not difficult to get it working with just pressure. First set the cut to 0 kPa, then drive around and watch the pressure as you engine break (release throttle), the pressure limit should be set just above that. Definately set it below the pressure you have with idle on a normally hot engine, which you seem to have tried to do.

It's also important to have a good VE tune and good ignition timing at idle, the engine should not have tendencies to fall through easily without any fancy features turned on (like overrun and idle control).  This can usually be fixed with proper VE and ignition tuning around idle are and there are some band aids, like "idle ignition advance control" and of course a real idle air control valve.

Just doing it with rpm cut/resume is probably an easier way out, and very easy to set up.

[rossi46numberone]

So....
How can I do if I want to work only with the RPM and throttle idle threshold :-\
Michele

[mattias]

Have you even read the "F1 for help" text ?

[rossi46numberone]

Yes for sure I read it, but don't find how to....
the F1 text :
"above this RPM,with TPS below idle threshold,all fuel is cut."
It seems to be simple ???
So if I follow this explaination I suppose that I don't need Kpa ?
Do I have to put zero on the "Fuelcut below(pressure based)" to enable the fuelcut RPM?
Is there another missed condition ?

[mattias]

It is that simple. Both overrun fuelcut methods can be used at the same time. They are not exclusive nor do they depend on each other.

Just set pressure to 0, and it will never cut fuel based on pressure as you'll never get that much vacuum in the engine.

What cut/resume RPM works on your engine with your driving style is for you to discover.

Using both methods at the same time requires you to think a bit further, which is not difficult once you grasp each method.