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Old 12-05-2002, 08:27 AM
Posts: n/a
Lightbulb explanation of milliseconds in defining load

Quote #1- from DEPETRY
"...Now, I have to say this graph is useless to me because the engine load units is in milliseconds and I dont understand how engine load can be expressed in those units. But I am sure the Mercedes engineers do...."

Quote #2
"... inspector 1 must not know what the fudge he is looking at..."

The graph is called the "DRIVE MAP"

Load expressed in milliseconds is in reference to the INJECTION PULSE WIDTH ie. time injector is open.

As we all know,INJECTION PULSE WIDTH is controlled by the ECU which at idle/low load seeks to maintain a lamda =1, it does this by monitoring the O2 sensor and adds/subtracts approx. .001 millisecond to the INJECTION PULSE TIME (ti).The amount of increase or decrease in INJECTION PULSE WIDTH is called the ADAPTIVE VALUE and is the value output by the ECU when reading live data stream from the O2 sensor in closed loop and the other various sensors at load.

At higher load- high RPM- larger volumes of fuel and air are needed (duh :^)). In order to maintain a lamda =1 the ECU monitors the upstream O2 and calculated load and compares it to the optimal values for the FUEL INJECTION PULSE WIDTH stored in the DRIVE MAP, If this INJECTION PULSE WIDTH does not equal 1 at the O2 sensor for the amount of air that the MAF sensor is sending to the ECU, it increases or decreases the PULSE WIDTH by a percent that is defined by the difference in lamda from optimal (1). This is defined as the SHORT TERM FUEL TRIM MULTIPLICATIVE If this value exceeds about 25% for more than apprx. 10 seconds a DTC is set for lean or rich state.

But in my enthusiasm, I digress.

Short answer, the Z axis of the graph- DRIVE MAP- is the programmed INJECTOR PULSE WIDTH

I really enjoy this tech forum, I have collected an entire library from the intelligent input from so many folks, I also find it challenging to try to understand the subtle factors that effect engine performance, and you guys are a great help.

Peace to all in the upcoming Holidays.
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