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The main flow calculation comes from BMWinjmon_vol_HppCmpn_C which is the base volumetric capacity of the pump stock this 500uL on B58g1 and 526uL on B58g2. This is multiplied by the pump volumetric efficiency from BMWinjmon_fac_HppEff_M and corrected for fuel temperature with BMWinjmon_fac_HppRt_T and then engine speed and some constants to give a final figure for a maximum volume flow rate.
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If this system is calibrated corrected, it will mean that at times of higher fuel system load, the load limit may reduced lower than “normal” levels. Rather than just prevent any of these safety subsystems from doing their job, we would recommend that they are actually used in a way that if everything operates as you intend they don’t cause a problem. Instead of trying to carefully craft your load limits to avoid the pump being maxed out, let this do it for you, not only that if the fuel load increases because, for example the lambda target is lowered for temperature control, the airflow will be reduced to keep the pump in a sensible operating range.
Disabling Injection Monitoring Load limitation
This is bad, but prior to now it’s been what most tuners have been doing, and we can see the effect of setting Load Limit Minimum - Injection monitoring to a flat 200% thereby preventing the load limit from this system dropping below 200%. You can see in the log below from a test to deliberately overload the HPFP, the fuel pressure drops to just 5Mpa which is “less than ideal” as the ECU tries to maintain high fuel demand (lambda target made rich for this test) at relatively high load. We now would recommend not to do this.
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HPFP Volume and Efficiency
The log and map values below show the effect of lowering the pump volume, causing the load limit to be abnormally low, limiting the MSV active angle to less than 100° with a further drop when the pump efficiency drops to 0.6 from 4000 to 4100rpm.
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Increasing the pump volume gives the following change, allowing the MSV angle to hover around 100º-105º instead of 90
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Load limit adjustment rates
The load limit adjustment rates cap the rate at which the cylinder fill limit is reduced and increased, increasing the magnitude of these gives the following result, a slow oscillation of the cylinder fill load limit, as there is a delay in the change of the cylinder fill limit or desired cylinder fill, to the actual fuel load reduction and reduction in fuel pump control angle.
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Upgraded HPFP
In the case where a higher flowing high pressure fuel pump has been fitted, it would appear that the main thing to do is update BMWinjmon_vol_HppCmpn_C to reflect the higher capacity, otherwise the ECU will trigger the injection monitoring load limit even though the pump has plenty of spare capacity, as seen below. The point at the cursor shows where the cylinder fill limit starts to actually limit the desired cylinder fill, after the injection monitoring limit kicking in at the peak of the fuel pump angle. However the limit is still in place with the pump comfortably within it’s operating range. In this case the solution will be to correct the pump capacity, and possibly fine tune the efficiency.
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Cylinder Fill limit reduction gain
BMWinjmon_fac_HppMax_M appears on B58g1 to be the cylinder fill limit reduction gain table, but the control seems best set with the overall pump capacity and efficiency table.