Bit of a run down on this table for all...
This table is a Lambda Equivalency Ratio table used by the ECM as one of the methods to limit the Air/Fuel Ratio of the engine. Of course Air/Fuel Ratio is the ratio air to fuel (by weight) entering the engine and the theoretical optimum ratio is called stochiometric. Stochiometric for a diesel is a ratio of 14.65:1, anything above this ratio is considered lean and anything below is considered rich. Even though the theoretical optimum air/fuel ratio is 14.65:1, in reality if you start going richer than 18:1-19:1 you start getting smoke.
The ECM calculates the engines air/fuel ratio (speed density method on the 04.5-09 and MAF method on 10+) and compares it against the Lambda Equivalency Ratio table and if the calculated air/fuel ratio is richer than what is in this table, the ECM will limit fuel output. So what is lambda and lambda equivalency ratio? First, lambda is just another way of expressing air/fuel ratio but is not specific to fuel type. In lambda the value of 1 equals stochiometric no matter the fuel type, so stoichiometric for diesel a 14.65:1 AFR=1 lambda, gasoline 14.7:1 AFR=1 lambda, methanol 6.5:1 AFR=1 lambda and so on.
To get from air/fuel ratio to lambda we divide an air/fuel ratio by the stoichiometric air/fuel ratio for the fuel type in use. For example, 18:1 AFR to lambda for diesel would be 18/14.65=1.23 lambda (rounded to 2 decimal places). But we still need to get to the lambda equivalency ratio to know what that smoke limit table is showing for the limits. To get to lambda equivalency ratio we simple divide stoichiometric lambda by our actual lambda, 1/1.23=0.813 lambda EQ ratio. Another way to express the lambda equivalency ratio is amount of fuel plus enrichment so, the 0.813 lambda EQ could be expressed as 18.7% lean of stoichiometric (1-0.813=0.187*100). If we go to the other side of stoichiometric, 12:1 AFR, and work through everything... 12/14.65=0.819 lambda, 1/0.819=1.22 lambda EQ ratio or 22% rich of stoichiometric.
For those that have played with this table and noticed that when you put larger numbers in this table you get more smoke under load coming out of the tail pipe, this is why. You are raising the limits for how rich the ECM is allowing the air/fuel mixture to get.
Couple things to note here:
- On the 04.5-07 engines, the fuel quantity limits that this table will come into play is between 50mm3 and 200mm3. These limits are adjustable in UDC Pro, HPT didn't include those boundary limits.
- If you play with your pulsewidth table and it is not accurate to the flow of your injectors, you've messed up the ECM's air/fuel ratio calculations, it will no longer accurately calculate (within its limits) the right air/fuel ratio it is running at.
- The 03-04 ECM's do have this table, it is much smaller and is in actual air/fuel ratio, not lambda EQ ratio.
Reply With Quote