[nirola]

hi,
i found this forum very very helpful but i have some specific query regarding santo which i would like to clarify.

since the day one my santro has this unique problem of increasing its speed outomatically. i mean even if i not press the padel it can, sometimes, go to the speed upto 40 kmph .

then we even went to the showroom and that guys attached electronic pad to the socket of car and checked the speed they said its OK.


what we analayised that if we start our car and INSTANTLY move, its speed increasing tremondusly, but if we wait for 20-30 sec before moving (switching to 1st gear) its normal. however i have not seen this problem in any other santro.


i hope this first post will help to my problem

kindly analyise..........

thanks

[speedsatya]

this happens due to the auto choke in mpfi cars ...when u start the car in the mornings or after a long time the rpm will be more ....once the engine reaches operating temperature the rpm comes down ...


this is normal ..nothing to worry about ...

[ryder]

This is becaue of the ECU (engine control unit), its a pre-programed electronic device which manages the engine at optimum level based on the inputs it gathers from sensors placed at varous places in the engine in real time (while the engine is running).

One of its functions is to reduce stalling of the engine, this it does by increasing the RPM of the engine when under load. That is the reason one can drive and ECU controlled MPFI car on a level road with out using the gas pedal, the ECU in this case manages the engine. But again this function of the ECU is to protect the engine against stalling and not to drive around in the same way. You can do it for a experiment tough.

My Indica also touches 35-40 kmph on a level road with out the use of the acclerator.

This is nothing to worry about.

Also, on cold starts for MPFI vehicles the engine runs at a slightly high rpm for the first few seconds (typically 15 - 40 seconds) and then settles down on its natural rythm, its better to let the car idle at this stage. Its good to move the car once it settles into its natural idling rpm.


Hope it helps.

Ryder

[chetanhanda]

The oxygen sensor on some MPFI cars does not have a heating element, it takes some time to come upto operating temperature.The 02 sensor provides readings based on difference in voltage above a specifc temperature.The ECU adjusts the RPM to mantain correct Air fuel ratio according to various parameters which involves the oxygen sensor as a major input. Since , in the morning/cold engine condition the reading sent to ECU is sent by a cold O2 sensor, the ECU thinks the air-fuel is lean so it increases the fuel, thereby increasing the RPM.
When the sensor comes to operating temperature the correct reading is sent and the engine comes down to normal RPM.

[chetanhanda]

Originally Posted by ryder

One of its functions is to reduce stalling of the engine, this it does by increasing the RPM of the engine when under load. That is the reason one can drive and ECU controlled MPFI car on a level road with out using the gas pedal, the ECU in this case manages the engine. But again this function of the ECU is to protect the engine against stalling and not to drive around in the same way. You can do it for a experiment tough.
Hope it helps.
Ryder

can you explain this.. ?