LotusTalk - The Lotus Cars Community - View Single Post

Kris from DRS · 06-02-2009, 07:12 PM

More on vaccum leaks and using software tools to help diagnose and protect the engine from over revs as a result of vacuum leaks:

In Accel / Decel:

Accel Constants:

RPM fuel cutoff limit should be from 2,200 to 2,800 range.

The lower the RPM the lower engine revs need to be before fuel injection turns back on.

TPS fuel cutoff limit should be around 11 to 12 for non-DBW cars (8 to 9 for DBW cars not using the controller, and 9-10 for DBW cars using our DBW controller).

If this value is below the closed-throttle position (TPS at idle) the fuel cutoff will not function. This means that when in decel (coasting off throttle the injectors will run at whatever the value is in the fuel map).

This is not a big deal, but is a waste of fuel and could cause some flames to shoot out of the exhaust in a high RPM throttle lift.

In some cases (in a race condition) sometimes the fuel cutoff is intentionally disabled (i.e. enter unobtainable values, such as 12,000 rpm and 125 deg throttle). Some engines can benefit from the cooling effect from the fuel running on into the cylinders. And in turbo engines this (combined with other things outside of the scope of this post) can be used to accelerate the turbine and create an "anti-lag" effect.

Back to the Accel/Decel TPS and RPM limits. If used properly this will not allow the engine to rev without intention. For example, if your throttle is closed, but you open another place in the intake (fuel injector o-ring seal, intake manifold gasket, etc...) the increase in air will have the same effect as if the throttle was opening. It hardly takes any fuel to rev an engine to the rev limiter without load. So, if the ECU knows to cut fuel if TPS is below X degrees while engine is above X RPM this will limit the engine from revving up.

How to monitor this function or test it: 2 easy ways.

In Data Controls you can monitor Injection time in units of Ms. When in decel fuel cut mode the injection time will go to zero.

On the top tool bar in the Editor, Under Syscon, Select System Flags, the Flag Monitor will open, the bottom right most column has the FLGCUT "buttons". When a FLAG is active it will turn on bright green color. The Overrun button indicates the Decel Fuel Cutoff function.

Kris

06-02-2009, 07:12 PM	#222 (permalink)
Kris from DRS Dynamic Racing Solutions Join Date: Oct 2006 Location: La Habra CA Posts: 343	More on vaccum leaks and using software tools to help diagnose and protect the engine from over revs as a result of vacuum leaks: In Accel / Decel: Accel Constants: RPM fuel cutoff limit should be from 2,200 to 2,800 range. The lower the RPM the lower engine revs need to be before fuel injection turns back on. TPS fuel cutoff limit should be around 11 to 12 for non-DBW cars (8 to 9 for DBW cars not using the controller, and 9-10 for DBW cars using our DBW controller). If this value is below the closed-throttle position (TPS at idle) the fuel cutoff will not function. This means that when in decel (coasting off throttle the injectors will run at whatever the value is in the fuel map). This is not a big deal, but is a waste of fuel and could cause some flames to shoot out of the exhaust in a high RPM throttle lift. In some cases (in a race condition) sometimes the fuel cutoff is intentionally disabled (i.e. enter unobtainable values, such as 12,000 rpm and 125 deg throttle). Some engines can benefit from the cooling effect from the fuel running on into the cylinders. And in turbo engines this (combined with other things outside of the scope of this post) can be used to accelerate the turbine and create an "anti-lag" effect. Back to the Accel/Decel TPS and RPM limits. If used properly this will not allow the engine to rev without intention. For example, if your throttle is closed, but you open another place in the intake (fuel injector o-ring seal, intake manifold gasket, etc...) the increase in air will have the same effect as if the throttle was opening. It hardly takes any fuel to rev an engine to the rev limiter without load. So, if the ECU knows to cut fuel if TPS is below X degrees while engine is above X RPM this will limit the engine from revving up. How to monitor this function or test it: 2 easy ways. In Data Controls you can monitor Injection time in units of Ms. When in decel fuel cut mode the injection time will go to zero. On the top tool bar in the Editor, Under Syscon, Select System Flags, the Flag Monitor will open, the bottom right most column has the FLGCUT "buttons". When a FLAG is active it will turn on bright green color. The Overrun button indicates the Decel Fuel Cutoff function. Kris __________________ Motorsport Components and Expert Service. Complete Lotus maintenance, installations, track preparation and specialty services.