FSD/PMD Relocation Kits

The Diesel Page has always been involved in helping to provide solutions for the 6.5 stalling issues that far too many owners endured in the 1990's through to now. In the beginning of our effort, we reported how dealer mechanics had tried to reduce the occurrence of PMD/FSD failure by relocating the FSD/PMD module. Some people thought the biggest problem with the PMD/FSD was excessive heat. Relocation seemed like logical solution to this problem. In reality, heat was just one aspect that determined whether a PMD/FSD would fail, but relocation was a step in the right direction, and it certainly made it easier to R&R the failure-prone Stanadyne module if it were to fail at a later date.

A company by the name of BETA was the very first vendor/manufacturer to introduce a PMD/FSD relocation kit (in early 2000), and I felt it was a step in the right direction. To help people learn more about the PMD/FSD problem, we (The Diesel Page) produced the following product review that appeared online here in June 2000 that outlined the problem, analyzed failures and discussed what was needed to improve reliability.

Nowadays, many PMD/FSD relocation kits and related components are available, some having a much higher level product quality engineering than others, but it all began with individuals looking for a better solution to a big problem. The D-Tech module has been on the market for more than 3 years now, and over time has fallen by the wayside as being less than perfectly reliable. At the present time I recommend the newest gray colored Stanadyne module. Stanadyne should have designed a new module like this one 20 years ago.

Here's the 2000 product review, as published by The Diesel Page.

FSD Cooler
Improved 6.5 Reliability
June 2000

By Jim Bigley

The patented FSD Cooler (#D450,044) is a product whose time has come. The Stanadyne DS4 electronic fuel injection pump began as a marvelous concept in diesel fuel injection, but it has produced enough problems to warrant finding a way to improve reliability. The FSD Cooler featured here may offer a cure for many of these problems.

As referenced in GM Technical Service Bulletin #77-63-06A, stalling, hard starting, and hesitation are symptoms of a failing FSD (Fuel Solenoid Driver) module. These symptoms usually (but not always) set a code 35 (or sometimes 36) in the 1994-95 models, or a code 1216 in the 1996 and newer models. Once a pattern develops, the problem will only get worse over time. While a diesel tech (or the owner) shouldn't overlook the basics in diesel troubleshooting, these 6.5 electronic injection system failures can usually be traced to the FSD module. The FSD module is the black box, about the size of a deck of playing cards, screwed to the side of the DS4 fuel injection pump.

In the original configuration, the FSD module is mounted to the DS4 injection pump to allow heat dissipation. The injection pump, being a fairly large mass (about 22 pounds) and being cooled by fuel flow, acts like a large heat-sink for the FSD module. In theory and from an engineering perspective, the injection pump should provide ideal heat dissipation for the FSD. However, reality has a way of disputing theory.

The large finned surfaces of the new FSD Cooler provides better cooling, and offers a couple other benefits we'll discuss in a minute. But first, I should mention that I first heard of experimental remote mounted FSD modules in 1997. Some GM diesel technicians had begun experimenting with this concept in an effort to reduce the failures they were seeing. The problem with these early attempts was the engineering and implementation of the idea. A Swedish company called Beta Machine has done that engineering, and has developed a product that was designed to reduce the number of FSD failures.

To understand why the FSD fails, it helps to know what this device does and what factors contribute to these failures. The 1994 and newer 6.5 fuel injection systems are "drive by wire", meaning there is only an electronic connection between the driver's foot and the fuel solenoid in the injection pump. Pressing on the accelerator pedal causes an electronic signal to pass from the APP (Accelerator Pedal Position) module to the computer, then to the FSD module mounted to the injection pump. The computer signal is then amplified by the FSD module, which in-turn drives a mechanical fuel solenoid inside the injection pump.

The FSD module contains a pair of high-power driver transistors that generate heat during normal operation. Knowing the FSD module drives the fuel solenoid approximately 7,200 times a minute at just 1800 rpm brings the operational requirements into clearer focus. These driver modules are worked very hard and generate significant levels of heat. Use more throttle, and the fuel solenoid is driven harder and for a longer duration.

This means the FSD will generate even more heat under high load or high-speed conditions. Tests have shown that even a low fuel level in the tank or a non operating electric fuel-lift pump will cause the FSD to work harder and generate more heat (See chart below). Add a high ambient temperature (or a dry, thin fuel), such as that found in the Southwestern US during the summer, and you begin to see why these heat induced FSD failures occur more frequently in those areas of the country.

Like any engine, your 6.5 is subjected to countless heat/cool-down cycles. All this expansion and contraction of the FSD module can cause a reduction in clamping load applied by the four original Torx screws. The relatively small-headed Torx screws are used without washers (as originally installed), which allow the screws to sink deeper into the plastic of the FSD module over time. This reduces the clamping load, and reduces the ability of the FSD to transfer heat to the injection pump, eventually resulting in an overheated FSD module and the onset of drive-ability problems. Note: This may explain why some owners experience a repeat of the same drive-ability problems every 20-40,000 miles.

Mounting the FSD to the new FSD Cooler uses GM's recommended screw torque along with a new set of allen head screws and washers. The new washers reduce compression of the plastic, which helps maintain the clamping load over time.

Once mounted to the new cooler, moving air cools the FSD, where fuel circulating through the injection system provided the cooling before. Instrumented tests performed by the manufacturer have shown the FSD Cooler is more efficient at cooling the FSD than when it is mounted to the injection pump. Better cooling means better reliability. Even while idling after a long hard pull, the FSD Cooler continues to have the advantage in cooling the FSD module. Idling presents the least "load" on the FSD, and therefore doesn't require as much cooling capacity as when the vehicle is moving (more airflow). In my tests, I discovered the FSD module just gets slightly warm after an extended idling period when mounted to the new FSD Cooler.

In addition to improving FSD module cooling, removing the FSD from the injection pump removes a huge heat load the pump has to deal with. This may improve reliability of the Optical Encoder/Temperature Sensor in the pump, as well as reducing the temperature of the fuel passing through the injection pump. Cooler fuel improves fuel lubricity (enhancing pump life) and hot re-starts, as well as offering a slight power improvement (cooler fuel is denser, and has more BTU per unit volume).

The new FSD Cooler uses a new heat transfer pad manufactured by the very same company that produces the heat transfer pads for Stanadyne, being a silicone treated aluminum foil. Unlike the pad used by Stanadyne however, this pad has cutouts for the transistors. This allows more radiated heat to escape the module, further aiding in temperature reduction. Removing the plastic covers from the power transistors also helps dump the radiated heat. Every little bit helps.

To effectively transfer heat, both the FSD module and the original machined injection pump-mating surface must be of a certain "smoothness". This improves heat transfer efficiency. Beta Machine measured the relative smoothness of many DS4 pump-mounting surfaces, and discovered they fell within the range of 0.40-0.44 Ra.

The new FSD Cooler also uses a machined surface for the FSD, measuring in the same Ra range as the DS4 mounting surface. Don't accept a knock-off product that doesn't incorporate anodizing and a machined FSD mounting surface.

Mounting surface smoothness is just one criterion enabling good heat transfer. The relative flatness of each mating surface must also match, and must not warp out of contact (in even the slightest amount). Any portion of the mating surface not making contact will reduce the amount of heat transfer capability. The new FSD Cooler is as flat as a precision CNC milling machine can make it, and is at least as flat as the DS4 injection pump-mounting surface.



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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

Copyright 2000 by TheDieselPage.com