The IDH/IDM combination is what calculates and controls how long and when the injectors open, should be under the passenger side wheel arch cover. Reminds me of the 50¢ mod where you place a quarter in the connector for the injector to block connector to keep the connections tight and prevent misfires. Hpop pressure is what forces the fuel into the cylinders, more pressure leads to more fuel being injected given a constant duration firing signal assuming everybody but 8 has enough fuel to fully reload.
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