Fuel cut
talskinyguy
11-23-2003, 11:20 PM
Fuel Cut
The ECM cuts the fuel supply, that is, it does not send the injector activation signals, in the following three situations.
The engine speed exceeds 7300 RPM (overrun protection).
The A/N reaches or exceeds the prescribed value (overboost protection).
The throttle plate is closed during engine deceleration above a certain speed.
Overrun protection.
Fuel is cut at 7300 RPM to prevent internal damage to the engine. The fuel activation signals are restored when engine speed falls below the threshold value. Adding a daughter board to the ECM can raise this threshold value. Our valvetrain is reported to be capable of 8000 to 8300 RPM without significant valve float or damage.
Overboost protection.
There is no sensor in the 3S cars to measure boost pressure. In 1996 and newer models there is a manifold absolute pressure (MAP) sensor, but it is used only for emissions purposes. The boost meter in the dash is a current-type meter that is controlled by the ECM. The ECM receives the air flow signal and engine speed signals and calculates the engine load. The boost meter is displaying the calculated A/N value rather than actual manifold absolute pressure. When the A/N exceeds a certain value at a particular RPM the ECM believes that excessive supercharging pressure exists and it stops sending the injector activation signals. Fuel flow resumes when the A/N falls below the threshold value. Note that overboost protection can occur at any RPM if the airflow is high enough (the threshold A/N changes over the RPM range). This overboost protection can be avoided by either reprogramming the ECM with a daughter board or by the use of an airflow signal conditioner (ASC) and larger fuel injectors. When larger fuel injectors are installed, the ASC reduces the airflow signal and the threshold value is rarely if ever exceeded.
Deceleration fuel cut.
Both emissions and fuel economy are adversely affected if fuel is delivered during closed-throttle deceleration at higher engine speeds. Therefore, the ECM does not send the injector activation signal during this situation. Once the engine slows, fuel delivery is resumed. The fuel cutoff speed and fuel resume speed depend on the coolant temperature, with both decreasing as coolant temperature increases.
The ECM cuts the fuel supply, that is, it does not send the injector activation signals, in the following three situations.
The engine speed exceeds 7300 RPM (overrun protection).
The A/N reaches or exceeds the prescribed value (overboost protection).
The throttle plate is closed during engine deceleration above a certain speed.
Overrun protection.
Fuel is cut at 7300 RPM to prevent internal damage to the engine. The fuel activation signals are restored when engine speed falls below the threshold value. Adding a daughter board to the ECM can raise this threshold value. Our valvetrain is reported to be capable of 8000 to 8300 RPM without significant valve float or damage.
Overboost protection.
There is no sensor in the 3S cars to measure boost pressure. In 1996 and newer models there is a manifold absolute pressure (MAP) sensor, but it is used only for emissions purposes. The boost meter in the dash is a current-type meter that is controlled by the ECM. The ECM receives the air flow signal and engine speed signals and calculates the engine load. The boost meter is displaying the calculated A/N value rather than actual manifold absolute pressure. When the A/N exceeds a certain value at a particular RPM the ECM believes that excessive supercharging pressure exists and it stops sending the injector activation signals. Fuel flow resumes when the A/N falls below the threshold value. Note that overboost protection can occur at any RPM if the airflow is high enough (the threshold A/N changes over the RPM range). This overboost protection can be avoided by either reprogramming the ECM with a daughter board or by the use of an airflow signal conditioner (ASC) and larger fuel injectors. When larger fuel injectors are installed, the ASC reduces the airflow signal and the threshold value is rarely if ever exceeded.
Deceleration fuel cut.
Both emissions and fuel economy are adversely affected if fuel is delivered during closed-throttle deceleration at higher engine speeds. Therefore, the ECM does not send the injector activation signal during this situation. Once the engine slows, fuel delivery is resumed. The fuel cutoff speed and fuel resume speed depend on the coolant temperature, with both decreasing as coolant temperature increases.
talskinyguy
11-23-2003, 11:48 PM
http://www.3si.org/forum/showthread.php?t=180749&highlight=top+speed+limited
http://www.3si.org/forum/showthread.php?t=156453&highlight=top+speed+limited
How many more of these will I have to post before you guys believe me that our cars are not speed limited, only rpm limited?
http://www.3si.org/forum/showthread.php?t=156453&highlight=top+speed+limited
How many more of these will I have to post before you guys believe me that our cars are not speed limited, only rpm limited?
powershifty
09-19-2005, 11:06 PM
So I have a 1991 dodge stealth. This spring, when I got her out of the garage. My car decided that it wanted to get what I believe is fuel cut at 11 PSI rather then then normal 16 PSI I usually get fuel cut at. I have a Greddy Profec -B and a stock fuel system, but for two years I ran at 15 PSI no problem. Now, all of a sudden, its 11. I already replaced my plugs and wires for fear of spark plug blow out, and that didnt work. Any suggestions?
Igovert500
09-23-2005, 01:07 PM
Pressure test.
talskinyguy, nice writeup. I completely agree, our cars are not speed limited in the least. Drag is the obstacle.
talskinyguy, nice writeup. I completely agree, our cars are not speed limited in the least. Drag is the obstacle.
93_R/T_TT_Stealth
09-23-2005, 11:46 PM
is it a bad thing if we were to say um... pin out our speedo :eek7:
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