Fixing Your PMD/Performance Tweaks
 

Note: The FSD/ PMD (same thing) is a small black box on the side of your injection pump. It is a signal amplifier that powers the fuel solenoid on your injection pump. It has 2 transistors mounted on it's backside that generate heat that has to be dissipated. In it's stock location it can over-heat and fail.

The story usually begins like this. You’re driving along and the engine just quits. You lose your power steering and the truck is very hard to steer. You pull over to the side of the road and you are able to restart. After a few days the stalls become more frequent and the truck will be hard to start. You realize that you can’t trust the truck and something has to be done. This is the classic symptom of a failing Fuel Solenoid Driver (FSD) also known as a Pump Mounted Driver (PMD). This is an electronic switch that controls the fuel flow on a Stanadyne DS-4 electronic injection pump. Electronic injection pumps are used on all Hummers with the GM 6.5 turbo diesel between 1996 and 2004. A failed FSD will not display an engine light. Pictured above the FSD is a small black box about the size of a deck of cards bolted to the side of your injection pump. It is an amplifier that receives signals from the engine computer to pulse the fuel solenoid which tells the injection pump to send fuel to the engine. It has 2 power transistors mounted on the back that generate heat that has to be dissipated. The injector pump is mounted deep in the center valley of the engine in a very hot environment. The FSD is exposed to heat that can cause it to fail over time.

The Stanadyne DS-4 pump has been used on GM trucks since 1994. Owners of older Chevy and GMC trucks and G-Vans have experienced these problems years before Hummer owners have. GM had so much trouble with early generation electronic injector pumps that they had to warranty the units for 100,000 miles. When AM General purchased these motors from GM they did not get a 100,000 mile warranty. In 1999 AM General bought the plant and took over production of the 6.5 engines later that year.

Heat generated by the FSD is supposed to be carried off by the diesel fuel flowing through the pump. While this is true, the damage is being caused right after the engine is shut down. After you stop the engine the fuel of course stops flowing and the water pump stops circulating coolant which in turn causes the engine temperature to actually spike for a short time. This is called heat soak. This rise in temperature heats the FSD which is bolted to the injection pump sitting on top of the engine. The continual heating and cooling cycles cause the FSD to fail over time.

There have been 3 variants of FSD's. FSD's with a 30214 on the case are the worst. This is the first generation and the most prone to fail. FSD's with a 34264 are second generation, and are preferred by some Stanadyne repairmen because they will either work, or won't work, like "a light bulb". The third generation number 34583 was designed to allow you to "limp home" by operating for a short while and then fail.

Because the injection pump is deep in the valley of the engine the FSD mounting screws are almost impossible to get at unless you remove the manifold (which is a major job. I've spoken to a couple of mechanics that were able to get the FSD out by using a very short torx bit wrench but I can't see how it was done. If your FSD needs replacing it seems unwise to put it back where it was, down in the heat. Why not save all the trouble and labor and simply mount the FSD on a heatsink somewhere away from the engine where it can stay cool. There are a number of aftermarket products that have specially designed heat sinks and extension cables that let you remote mount your FSD in a cooler spot. The kit used in this article is from Flash Off-Road. This solves the problem once and for all. FSD’s have a calibration resistor pack that describes the pump to the electronic control system. Because there is variability in the manufacturing of injector pumps the resistor is used to calibrate the engine computer to the pump. The resistor pack is a small circuit board with a resistor that is inserted deep into the FSD’s socket. New FSD’s don’t come with resistors. The #5 calibration resistor is considered the "average", and almost any pump will work with a #5 resistor. The resistor is only used when the control computer forgets what the value is, which occurs after the batteries are disconnected or a hard reset is performed with a tech tool. If you don't use a resistor you will get a p1218 error code when the computer tries to read the value. Your truck will still run. Whenever I run into a failed FSD I always replace it with a remote mounted unit on a heatsink and just abandon the defective FSD on the injection pump.


INSTALLING A REMOTE MOUNTED FSD

Remote mount FSD kits come with a heatsink, heatsink compound, terminal grease, mounting hardware and an extension cable. If you get a brand new FSD it will come with a heatsink pad / gasket. Use this instead of heatsink compound.

The terminal grease is a thick plumbers silicon grease you can pick up at a hardware store. It's used to coat the seal on the water tight silicon rubber connectors so the elements don't corrode your connections which will stop your truck from running.

First Decided Where You Are Going to Mount the Heatsink

While I’ve seen the FSD’s mounted in many places a good place to mount the new heatsink on a Hummer that isn't used off road is near the battery compartment on the right side of the truck. It’s away from the engine, fairly clean and gets good air circulation. If you go off road and kick a lot of mud up into the wheel well you can clog the fins. This heatsink is mounted on the Battery hold down bracket. Just make sure the hood will close. This installation has plenty of room. On 2000's and newer trucks the plastic electrical cover is a very good out of the way place that stays clean and has very good air circulation. If you have a 98 or older a real nice place is on the horn bracket. You wanted to get rid of those lame stock horns anyway. You have to get to the injection pump so depending on the year of the truck you will have to move the big black rubber air intake hose that sits on the top of the engine out of the way. This usually involves loosening a few hose clamps and pulling the hose free. Reach down to the wiring harness going to the FSD and lift up on the tab and pull the plug out of the FSD. If you’re going to remove the old FSD or resistor now is the time. Some mechanics say that they can remove the resistor from the old FSD while it is still mounted on the pump by using a small snap ring pliers with a dental mirror and flashlight to grab the two small holes in the resistor pack and pull it out. I say "no way". I've looked at this and tried it a few times and never was able to do it. I can't even get the resistor out of the FSD with the FSD out of the truck. I usually just get a new resistor which will cost between 20.00 and 30.00 dollars.

How to Remove the FSD

If your FSD isn't defective and or you want to salvage the resistor try this method to remove the FSD without having to take the the truck apart. I'm cheap and wanted to save the 30 bucks for the resistor or better yet the 300 bucks for a new FSD. If you're careful it isn't hard to break the old FSD off the side of the injection pump. You don't want to somehow break your injection pump or cut a bundle of wires in a harness. First cover up the air intake with a rag to prevent the possibility of loose bits of old FSD from getting in the engine. What you do is very carefully place a hack saw blade diagonally across the top corner of the FSD facing the firewall . Position it so it's on the plastic right next to the metal base. Move any wiring harnesses away so they don't get cut. Saw about 1/4" deep into the corner so you go through the mounting bolt. Take a screwdriver and tap it in between the FSD and the pump. Work the screwdriver around while gently prying. The mounting screws all just snapped and the FSD fell off the pump. In fact as you can see in the picture the metal in the corner of the FSD cracked off probably because I first put the screwdriver in the sawcut and not between the FSD and the injection pump. If your old FSD is defective you want to get the resistor out of the socket in one piece. If you're reusing the FSD leave the resistor in place. Put the FSD in a vise so the socket is facing up. Take a hacksaw and carefully cut the plastic socket in two places. Break back the tab of plastic and the resistor and pins will be exposed. Take a small screwdriver and push the resistor off the pins. Insert the calibration resistor into the new FSD with the resister number facing up, Notice that there is a tab on the resistor pack that meshes with a cutout in the socket. If you put this in the wrong way you won't be able to remove it without destroying it so make darn well sure you get it right the first time. One of my readers sent me some information on how he gets the resistor out of the fsd. He fashions a spring clip out of a large safety pin. He cuts off the head and bends the ends out so they will engage the holes in the resistor.

Assembling the PMD to the Heatsink

Next you want to mount the FSD to the heatsink. You will need 4 - 1" 6-32 screws. If you are using new screws get some stainless steel hex head cap screws. The heads on these screws are small enough to drop down in the FSD counter sunk holes. If the screw heads are too large to drop down you will not be able to correctly tighten the FSD to the heatsink. When I couldn't find hex head cap screws I've bought Phillips head screws and had to grind off some of the diameter so they drop down. Coat the bottom of the FSD with heat sink compound or use the heatsink pad and mount it tighting to 25 inch pounds. This is fairly tight. An invoice for a FSD that I recently bought (11/2007) said that if the FSD wasn't tightened to 25 inch pounds it wouldn't be warrantied. I like to use locktite blue on the heatsink mounting screws. Smear terminal grease on the silicone plug gasket and insert it into the socket on the extension cable. Make sure the cable locks together. If it doesn't I've had to file down the flat surface of the extension cable so it engages the locking tab. Leave the ground wire attached to the injector pump. Route the cable over to the new location keeping it off hot surfaces. I like to clamp and wire tie it so it doesn't move. In this case we are going to mount the cooler on the plastic face in the battery compartment. The Hummer's batteries are far enough away and are sealed units so there will not be a problem with battery acid or corrosion. If you are going to be doing lots of muddy off roading you do run the risk of getting the cooling fins full of mud in this location. The 6' cable will allow you to mount the cooler almost anywhere you want. Others have mounted it near the center of the firewall, near the air inlet in the radiator stack or near the radiator overflow. Trace the outline of the FSD on the black plastic shield next to the battery and use a saw or rotary tool to cut out a hole for the FSD to fit into. Put the FSD into the hole and mark the 4 heatsink mounting holes and drill them out. Mount the heatsink to the plastic shield and plug in the extension cable using terminal grease. If you go playing in the mud make sure that you wash off anything plugging up the fins of the heatsink. When I mounted the heatsink on the horn bracket of my 98 I ground off the 2 horn mounting tabs and smoothed the surface. I located and drilled 2 holes in the heatsink and bracket. I primed and painted the bare metal bracket to prevent rust. We finally had a little rain here. The windshield wipers were going and as they moved across a spot on the windshield they seemed to be scraping over some frozen spots except it wasn't freezing out. I didn't think anything of it. A couple of days later the sun came out. I was at the gas station fueling up and cleaned the windows off. When I got back in the truck I saw a bunch of very small black spots on the windshield. I first though I had driven by someone who was spray painting so I figured I'd just take a razor blade to the windshield when I got home. Then it hit me. When I ground off the horn brackets I had sparks flying everywhere. The little black specs were from the grinder. Luckily the razor blade cleaned off the specs. The moral of the story is to cover up the area you are grinding in especially the windshield.

A Technical Discussion About the FSD/ PMD.
by Peter Hipson 11/15/2005

This all started when I made the comment that the PMD (pump mounted driver) has 2 - 500 watt transistors and would seemingly have to dissipate 1000 watts of heat. Actually it cannot dissipate more heat than the power it draws from its power source, the PCM. The PCM is powered by two circuits, one battery circuit that feeds the PCM, and the truck's brake lights. This power is used solely to keep the PCM's memory alive, and a few key-off tasks and represents a minimal amount of power consumed, none of which is sent to the PMD. The second power source keyed to the ignition feeds the PCM. This source has a 20 amp fuse. Fuses are expected to blow at the amperage they are rated at, so if you wanted 20 amps, you'd need a fuse larger than a 20 amp fuse. In the electrical engineering game we use a figure that is about 70 to 80% of the fuse ratings, so a 20 amp fuse would be expected to pass about 16 amps steady state. So we have the potential that the PCM (which includes the PMD driver module) drawing 16 amps. But...The same power fuse also feeds the fuel pump! Now, though many don't realize it, the fuel pump is rather inefficient electrically! It typically draws 5 to 7 amps when running! That leaves us with 10 amps for the PCM and the PMD. That's perhaps 130 watts of power. However we must take into consideration other parts of the PCM that draw and utilize power. The actual computer module draws and uses power, perhaps an amp or so. (Say 10 to 15 watts). The Injector pump's solenoids and timing stepper motor also draw power (which is eventually converted to heat...) and these actually do draw a significant amount of electricity, maybe (let's be generous, and say 5 amps, you'll see why in a few minutes). The PMD/FSD driver is in series with the solenoids. Something like a big electrical switch. The current through the PMD cannot exceed the power drawn by the solenoid, in fact, if the signal was a constantly varying saw tooth, or a sine waveform (the worst to control) the average power dissipated by the PMD would be equal to half the power drawn by the solenoid. So, say 2.5 to 3.0 amps. OK, at 3 amps, we're talking about 36 watts of power that the PMD dissipates. That's a long ways from the power dissipation that we see quoted so frequently. However, this amount is still significant at 36 watts in a package the size of a deck of cards would make the unit too hot to handle after a short while (say 10 to 15 minutes.) However, that is not the problem with the PMD! Silicon devices are designed to work in one of three environments. The consumer grade devices are designed to be used in an ideal environment, not too hot, not too cold. Commercial devices are specified as 0 to 70 degrees C for their working temp. The other end of the scale is military specifications. These are typically -55 to +125 degrees C. That's really, really cold, and quite hot. In the middle are devices designed for rugged commercial applications, such as automotive, where the range is between these two extremes (usually -25 to +100 degrees C) which is what the PMD's devices should be rated at. I doubt they use military grade devices in this device! The problem is that the injector pump is eventually going to get about as hot as the engine. The engine temperature at operation can be estimated to be 85 to 90 degrees C. That is 10 to 15 degrees less than the temperature of the devices! The PMD will create its heat increase (delta t) without regard for ambient temperature. That is if the PMD temperature is 20 degrees C, and as it operates it increases by 40 degrees C (to 60 degrees C) then if it starts at 85 degrees C and increases that 40 degrees, it will get to a temperature of 125 degrees C! Well above the design limits of the device. The stock PMD/ FSD was designed to get cooled by fuel running through the injection pump. This arrangement works well until outside temperatures heat up. In locations like Arizona and Southern CA where the temps run over 100 degrees in the summer you see more FSD failures. When we design heat sinks, we specify their efficiency as being a certain number of degrees of temperature rise per watt of power applied. Typical designs range from about 0.75 degrees per watt (very efficient, and probably very large too) to as much as 6 or 7 degrees per watt (less efficient.) Above we said that the PMD may dissipate in a worse case about 40 watts. Mounted to a heat sink this would translate into a temperature rise of about 30 degrees for that really efficient heat sink, to 260 degrees for that really poor one. The heat sink size would have to be between these two values, and if we use an ambient temperature of 48 degrees C, and a maximum temperature of 100 degrees C, we have about 52 degrees C to play with. We see we need a heat sink that will give us a rise in temperature of not more than 1.2 degrees per watt. The above is worse case design. Maybe smart design, too. But in the real world this calculation is very conservative. The PMD only dissipates a small fraction of the heat that the above calculation implies because it is basically digital (A pulse width modulated signal) and it only dissipates heat when it is changing state from on to off, and off to on. When fully on, the dissipation of heat becomes a factor of the voltage drop in the transistor .With a standard silicon transistor, that would be 0.7 volts, or with 5 amps about 3.5 watts. A FET is much more efficient, and would probably only dissipate maybe 0.5 watts when fully on. The fact (if it is a fact) that the transistors are rated at 500 watts, indicates they are FET's. But since they are in a TO-5 case (that diamond shaped package) tells me that someone simply multiplied the maximum voltage and the maximum current for the transistor and came up with a number. A TO5 case limits power dissipation to considerably less than 500 watts, as there is insufficient surface area contacting the heat sink to move that amount of power. In summary, the PMD can only create about 40 watts of heat which is all the power it receives, and it can't create heat from nothing. However, 40 watts of heat can be significant, and does require a heat sink to get rid of the heat.

FSD Part Number Characteristics

Starting off - the Stanadyne DS4 injector pump (as an overall unit, including the PMD) has gone through over 20 revisions since it's introduction. Many of the improvements are internal, but 2 of the
improvements are involving the PMD itself.

Introduced in 1994, the (pretty accurate) rumor mill out of Detroit has Stanadyne losing the argument with GM about the placement of the DS-4 injector pump, which we all know is in the middle of the "V" between the valve covers. This unfortunately places the injector pump electronics in the middle of a ton of heat. The heat is balanced (in theory) by the fact that the PMD is being cooled by the diesel fuel itself running through the pump. In theory, this is true, in actuality - the damage is being caused while the engine is OFF, not while it's running. Reports have shown that the pump itself will peak in temps around 140-150 degrees F. When the truck is off, the heat soak will push the temps to anywhere from 180 to 200 degrees, depending on ambient temps of the season and location. The reason why the unit fails (from reports via Stanadyne dealers and Diesel Forums) is basically the transistors themselves will lose connection due to the epoxy compound (used to seal the unit together) weakening, eventually allowing the transistors to literally work their way loose. It's a bad design overall, compounded by continual heat/cool/heat/cool cycles. Add to the issue that you need a good and clean ground (the case itself provides some of the grounding!), and you really have a major issue if the mounting screws start to oxidize. Getting technical, it seems (from what I can tell by looking at a destroyed PMD) that the unit is basically a huge set of transistors (one of them I believe is a Darlington) in which one triggers the other to fire an electrical pulse, and will vary the pulse based on the input from the PCM. I'm not crazy about the design myself. The dual layer PCB has a tendency to delaminate, and the board design (when looking at the reverse engineered designed diagram) should have been far more robust for a diesel workhorse engine. Getting to the specific PMD question you're posing - what we are seeing here is classic failure of first and second generation PMD's. This is something that owners of 1994-1996 Chevy and GMC trucks and G-Vans have experienced years before Hummer owners have. Because AM General didn't put in the 6.5L TD until later on in the engine's life span, non-Hummer owners have experienced these failures way before Hummer owners will. Add the fact that many Hummer's aren't daily drivers (mine is!), and you extend the lack of issue visibility even further. GM had such a problem with PMD's and early generation injector pumps that they had to warranty the units for 100,000 miles. According to Stanadyne rebuilders there have been 3 variants of PMD's, with the latest one being either an improvement or a problem, depending on who you talk to. PMD's with a 30214 on it's case are the worst. This is the first generation and the most prone to fail. PMD's with a 34264 are second generation, and are (ironically) preferred by some Stanadyne tech's because they will either work, or won't work, like "a light bulb" according to one tech. A Stanadyne tech in Ontario, Canada (note the location - definitely a low risk of heat soak in that area!) has gone over 100k with a second generation PMD. The third generation (34583) actually has gone through some mini-revisions of it's own. This unit was designed to allow you to "limp home" (yeah, right) by operating for a short while, then fail. The latest variants of the third generation are the most sought after versions. Other problems include a bad injector pump and the Fuel Solenoid Driver module (FSD) that sits on the injector pump on a turbo diesel only. Stalling, hard starting, and hesitation are symptoms of a failing FSD module. This is a common problem. This part is composed of two 500 watt power transistors mounted to the drivers side of your injection pump. It seems that this electronic module overheats and goes bad. The engine will probably start when it's cold and have a hard time as it gets hot. If the engine doesn't start It was suggested that you pour some water on the left side of the injection pump to cool off the driver. You have to remove the injection pump to remove and replace the FSD although I've heard from some mechanics that they have removed them by using a very short torx bit wrench (below). They may have ground one down to fit in the narrow space. One owner was able to remove the FSD with a heavy duty "putty knife" (the kind where the blade goes through the entire handle and you can hit it with a hammer) I sheared off the thin torx screws attaching it to the pump and remounted the new one to a cooler and reused the resistor that was embedded in the socket. Owners have told me that the best way to go is to get a unit that has a remote mounted heat sink off and away from the hot engine. There are a number of after market products that have a specially designed heat sink that lets you mount a new driver in a cooler spot which should solve the problem once and for all. If you get a new FSD you will need a new calibration resistor pack for $20. The resistor describes the pump to the electronic control system. The resistor must match the pump, not the FSD/PMD. When I purchased the FSD, there was no resistor with it - I had to buy one separately. I believe that if you get a complete pump & FSD, a new resistor (matching the pump) will be included. The #5 is considered the "average", and almost any pump will work with a #5 resistor. The resistor is only used when the control computer forgets what the value is, like after the batteries are disconnected. If you don't use a resistor you will get a p1218 error code when the computer tries to read the value. You can get the computer to see the new resistor by initiating a TDC Learn with a tech 2 scan tool. The computer will check the resistor value on it's own every 50 startups. Don't even know the value of the one that's in there, but the p1218 code is gone now since I stuck in a resistor from an old FSD. The resistors are keyed for correct installation. Notice the curved top and the alignment tab in the socket. The resistor number faces up. You can see the number printed on them by looking at them. Use a dental mirror and a flashlight. To remove them, use small snap ring pliers. There are two small holes in it that you can hook the pins into to pull it out. I was able to do this without removing the FSD from the 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 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. Depending on the problem the truck may go into 'limp home' mode. When the timing signal is 'missing' the system will advance the timing to the max, hence the engine will get very noisy. The trans doesn't up shift and you can drive about 30 MPH. Your engine will be running at higher RPM's due to this. My 97 turbo diesel wagon would stop running for no reason at very unexpected times. After checking the fuel lines, lift pump and changing the fuel filter, I took it to a GMC dealer to have them run a computer scan on it. The scan from the tech 2 came back with the codes P0251 and P1216 both indicating a bad injector pump. The codes being generated are generic OBDII codes that correspond to problems (on the 6.5L TD engine) that eventually will lead to the Injector Pump or the Pump Mounted Driver being replaced. You may not find them in the AMG Service Manual. p0251 (Injection Pump Fuel Metering Control) is the generic OBDII code that gets reported when the Stanadyne Injector pump can't read the optical sensor properly. p0370 (timing reference) is generally referring to the PMD or the electronics behind the optical sensor. p0251 will throw a "Check Engine" light. p0370 will not. Getting a p0251 will generally give you something else paired with it. Definitely have the injector pump/PMD diagnosed. Best case - you dump a bunch of Stanadyne Fuel System additive in for a few weeks, clear the code out with the OBDII tool, and you'll never get it again. Worst case - you replace the Injector Pump and/or the PMD. My Hummer has only 51,000 miles on which I do not think is a lot for this kind of diesel engine, so I called Stanadyne the manufacturer of the injector pump . After I read them the codes they explained that the optical sensor in the pump had failed. They gave me the model number of the pump used in all diesel hummers DS5521.

FSD Calibration Resistor Values Resistor No. Ohms Fuel Change MM3/Stroke
1 4300-4500 -4
2 7200-7400 -3
3 9800-10100 -2
4 13100-13500 -1
5 17500-18000 0
6 27700-28300 +1
7 43700-44700 +2
8 58400-59600 +3
9 79800-81400 +4

THIS IS THE WEBSITE THE ARTICLE WAS TAKEN FROM, REMEMBER, THIS WAS FROM A HUMMER SITE.......
http://flashoffroad.com/Diesel/injectionpump/fsd.htm

Good reading...

need help fixing my pmd!
 

im having real trouble getting my pmd fixed. i have an rv/campervan with a 1996 6.5 chevy motor. i am experiencing the same problem as every else with the pmd but unlike most people me and my truck are stuck in bulgaria, eastern europe!!!. there is no one and no where in eastern europe who has the know how or the tools to fix it. i have read the excellent description of the problems and how to fix it but dont trust my self with the job. there is written "mercenry mechanic, have tools, will travel". who ever you are i need your help!. if any one can help me in any way i would be so greatfull, my poor truck has been stuck here for 5months!!!!!!. thanks

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:argh::argh::argh::argh:

Okay, I'm lost I've got one with the p0251 p1216. Same symptoms as a PMD BUT with alot louder injector rattle (more so than a normal 6.5) thats eliminated when I come back to Base timing with the actual timing running around 3.9deg.

I'm concerned to drop a PMD in this thing and it be a pump issue. Low power all the time and p0251 shows with 0 RPM 0 Load in freeze frame, P1216 shows with 1,200 + RPM

a bad injector can sometimes result in a loud ticking which what that injector seems like its on its way too when the timing is advanced a little bit. its not a pmd symptom. p0251 is fuel metering a malfunction cam/rotor/injector and p1216 isnt listed but if you mistyped there is 1226 and that is injector output circuit.

im with you i really doubt its a pmd. the engine harness can sometimes rub against manufacturing mistakes that are sharp and break wires and also dirt and heat can kill wires too so maybe you need some new wires. its a lot cheaper than a new injection pump

Excelent Mechanic Help
 

:U:Excelent explanation for all question about mechanic, Im very happy
with you web-page
Lou:U:

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Question: I Have PMD # 34583. I want repair and keep for spare.
Can you tell me about repair or internal parts
Thank you
Lou:humm: