The new FSD location also takes into account the length of the existing wiring harness. The new remote location places no more strain on the primary portion of the wiring harness than that of the original pump mounted location. In fact, I found an additional couple inches of wiring length available after everything was in place. I did however, find the ground wire a little too tight in my installation. I solved this by splitting the shrink tubing, allowing the wire to ride farther up the harness (see circle in photo). A couple wraps of electrical tape over the slit completed the harness installation.

For those who wish to mount their FSD Cooler at a remote location, Kennedy Diesel (see source listing at the end of this article) offers hi-quality FSD extension harnesses that maintain the all-weather protection offered by the original GM electrical connectors.

Total installation time was about 30 minutes, but I think I could do it a second time in 10. These times do not include removing the original FSD from the injection pump. Removing the original FSD would require removal of the intake manifold, and rotating the injection pump (in some cases). The only tedious part of the installation was unplugging the FSD connector and re-routing it above the intake runner. As instructed, I used a screwdriver to upsnap the connector lock, then push the connector off the FSD. Once off the FSD, I used a piece of wire with a hook in it to pull the connector and harness up over the intake runner.

Prices for a new FSD module have ranged from $168 to about $240 USD, so you'll have to decide if the work involved in re-using the original FSD is worthwhile. In addition, you'll need a new calibration resistor pack if you don't re-use your original FSD. These run about $15. All of these products are available from the vendors listed below. Otherwise, a Stanadyne authorized service center could supply you with a new FSD (pn-34583) and calibration resistor pack.

FSD calibration resistor packs (example on the left shown larger than actual size) are used to calibrate the maximum fuel delivery of the Stanadyne DS4 electronic fuel injection pump, and are available in nine different resistance values. These calibration resistor packs are inserted into the connector shell of the FSD. Most DS4 pumps use a resistor with a calibration ID value in the range of 4 to 6. Stanadyne defines fuel delivery in mm3/1000 injection strokes. The DS4 supplies between 61 and 64 mm3/1000 strokes at full load. The fuel delivery change between each resistor step is 1.0 mm3/1000 strokes, which equals approximately 1.5% more fuel per resistor step. Unless you re-use the resistor pack from the original FSD, a #5 resistor would be a safe choice.

Note: Experts report that the 1994 and newer 6.5 computers only look at the FSD calibration resistor value whenever the TDC-Offset timing procedure is performed. Installing a different value calibration resistor pack (or installing a variable control) may not provide a change in fuel delivery, unless you have the timing re-set using a Tech II Scan Tool each time you change the resistor value.

-Manufacturer supplied chart-
Average FSD* temperature after 100 km driving distance at 100 Km/h and 25°C ambient temperature.

Conditions with high fuel level
Pump mounted 73° C, 163° F
FSD Cooler mounted 55° C, 131° F

Conditions with low fuel level
Pump mounted 89° C, 192° F
FSD Cooler mounted 55° C, 131° F

Conditions and hauling an enclosed trailer
Pump mounted 98° C, 208° F
FSD Cooler mounted 58° C, 136° F

Conditions with a non operating lift pump
Pump mounted 103° C, 217° F
FSD Cooler mounted 58° C, 136° F


* New FSD modules #34583 were used in these tests.

Test vehicle: 1997 K2500 – 4WD – automatic – 4.10 rear end – 245/75-16 tires – 3901 Kg GVWR – AC turned off.

“The difference in FSD temperature between the two mounting positions will be even greater with "dry" diesel and/or at higher ambient temperature.” Beta Machine

If there's a negative in having an FSD Cooler, it's that you will lose the ability to re-install the "Turbo Power" engine cover. As we've learned over the past couple years, we really ought to be running without it anyway.

The intake manifold and injection system will run a little cooler, and you'll be able to service the fuel filter assembly without as much fuss. Seems like a worthwhile trade-off for the potential improvement in DS4 reliability.

In closing, I would like to mention that Stanadyne has made many improvements to the DS4 fuel injection pump through the years. The newest pumps are a more mature product than they were in 1994. While the 1994-95 models were most problematic, those injection pumps newer than about mid model year 1996 (DS4-5288) are leaps and bounds ahead of the earlier models in reliability. Those who have followed The Diesel Page know that we see more of the problem trucks (as a percentage) because of our focus on problem solving. This skews 6.5 owner perception somewhat regarding DS4 reliability. I've owned a 1994 6.5TD now for two years and haven't had a single injection system problem. With so many 1994 and newer 6.5TD trucks now out of warranty, any product that could potentially reduce future maintenance costs and improve reliability should be considered. The FSD Cooler could very well be that product. The Diesel Page

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