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Pump Calibration Resistors

The Stanadyne DS4 pump is fine tuned by a small resistor “chip” that installs inside the wiring cavity of the PMD (pump mounted driver) and slips over the pins. Resistors are available in steps ranging from 1 through 9. Each step in resistor value will alter the fuel delivery by .5mm3. When a pump is built or rebuilt and the calibration is spot-on, it is equipped with a #5 resistor. This is the target value when building a pump. This leaves 4 steps upward to #9 or a 2.0mm3 potential increase in fuel delivery. Based on a 62mm3 program, this is a very slight increase especially when compared to an aftermarket chip or program that runs at 68mm3, 72mm3 or even up to 80mm3!

I have run #5, #9, and #13 resistors, and can assure you that simply swapping them OR using a variable (fuel control) will NOT alter fuel delivery. It WILL do so on the Stanadyne test stand, and it WILL do so upon the resetting or loss of the value stored in the PCM, but will have NO immediate affect.

Case in point: We frequently hear of 6.5 owners having their PMD replaced only to get a DTC 56 (Injection Pump Calibration Resistor Error) several months down the road. This condition will not reset until a proper value resistor is installed.

So what triggers the re-learn of this value? From my observations, initiating TDC learn (scan tool clears PCM memory) will do so. I also surmize that a given number of startups (key cycles) will cause the PCM to “recheck” this resistor.

During development of our laptop scan tool package (94-5 diesel specific) we encountered a table titled “Pump calibration.” The vehicle in question had a 115 value logged and was equipped with a #5 resistor. Upon plugging into another driver with a #9 and restarting the engine, the value remained the same. Upon initiating TDC learn, the value changed to 145. Removing the resistor had no effect. TDC learn with no resistor caused the value to change to 95 9and set DTC 56) which is the lowest setting. The aftermarket #13 will also set DTC #56 therfore I will no longer be offering them for sale.

To summarize: I generally recommend the use of a #5 resistor when swapping out drivers. This, being the middle of the road setting, provides a nice safe setting. If one has the ability or desire to have a slight increase in fuel delivery, as evidenced by EGT readings, one could put in the #9 resistor, but remember, it will not change until TDC learn is initiated or the PCM loses its memory.