B
Bernie
Guest
(Note: This is a repost of a thread I did about this on another forum back in January)
Well, my new PMD (pump mounted driver) and relocation kit arrived today, but too late to install now. (I hate working by flashlight)
I'll install it tomorrow and take some pictures of the process because I've noticed that there are very few places on the net that actually show how to do it. And mine will be "fun" to do because, unlike every other 6.5l I've found pictures of on the net, the position of my a/c compressor is reversed with the alternator. I'm not sure why this is, but every other photo set I was able to find of how to change the PMD shows the alternator on the driver's side, which leaves just enough room to get to the PMD. With the a/c compressor there though you can't even see the PMD, or the injector pump it's mounted to, which means the intake has to come off to get at it.
(question was asked, "What is a PMD?")
On the 6.5L GM diesel with the DS4 injector pump (after 1994) there are two pumps, the lift pump, which brings fuel up to the fuel filter at about 5-7PSI, and the injector pump, which pressurizes it for the injectors. The injector pump is electronic, and the module that operates it is called the PMD, or pump mounted driver, because it's actually bolted to the side of the pump. It's also sometimes called an FSD, for fuel solenoid driver. The module has two heavy transistors in it that control how the pump works, and those transistors get pretty hot. Some genius at GM figured that if they mounted this to the side of the injector pump the fuel flowing through would keep it cool. Nope, it doesn't. In fact, because the injector pump is mounted in the intake valley, between the two heads, and because GM added a fancy plastic cover to the intake, it's one of the hottest spots in the engine compartment, and these modules have been failing every since. Typically, an OEM PMD will last about 75k (mine went at 77k). There have been some improved PMDs made, that are supposed to handle the higher temps, but I've heard of those failing from the heat as well. In addition, while the intent was to keep the PMD running cooler with the fuel flowing through the pump, no one seems to have thought that the opposite was also true, the PMD heats the fuel. In the winter that's not bad, and actually helps at low temps when diesel can gel, but in the summer, that extra heat can really thin out the diesel, making the pump itself work harder, and with less lubrication, leading to early failure of your $1,400 injector pump.
What most 6.5L owners do then is relocate the PMD to a better spot, and use a proper heatsink to cool it. Many of these bolt to a couple of studs on the intake, raising the PMD up into cooler air (and airflow from the fan), while still being able to reach it with the factory plug. Others have even gone so far as using harness extensions and mounting the unit inside the front bumper, getting out of the engine heat zone altogether.
My new PMD will be mounted to the intake and use the existing plug. While it would run cooler and last longer if I put it outside the engine compartment I dislike the idea of having it where an otherwise mild front collision, that you'd normally be able to drive home from, can crush the PMD and kill the engine. Also, that's less wiring to have to bother with, and less things that could go wrong.
Normally, installing a new PMD this way is a 15 minute job. Just bolt the new one to the intake (it's pre-mounted to the heatsink), pull the plug from the old PMD and plug it in the new one, shift the ground wire over to the new one and you're done. No need to even remove the old PMD from the pump. It's a tight fit reaching the plug though, and you have to fish it out with a coat hanger, but because my compressor is mounted on that side you can't even see where the plug is, so I have to either unbolt the compressor and shift it to the side, or unbolt the upper intake manifold and move it aside to reach the old PMD.
Just to give you a better idea of what I'm talking about I have some photos.
Here's what the injector pump looks like. The PMD is the black box on the side, marked FSD in this picture.
Here's where the pump mounts on a typical 6.5L (this is in a Hummer) The shut-off solenoid is to the left (front of engine) and the fuel solenoid is to the right (rear of engine) which places the PMD at the bottom, down under the radiator hose in the photo.
Now, here's my engine. Note how the condenser line and compressor pretty much block all access to the injector pump and PMD.
(a few hours pass by)
Well that didn't quite work out the way I planned...
I really wish this part had shown up earlier yesterday. Today it's almost 60, sunny, but with 23 MPH winds and gusts of over 40. Yesterday was pretty much the same, but without the wind. You'll see why that's important a little further down...
Okay, so it's 2 PM and I have about an hour and a half to work on the truck before I have to take the cat to her vet appointment. The truck runs well enough to get her there, but this is the only time I have to work on it so...
First, as you might know, the truck does not fit in my garage, which means I have to work on it outside, on a 30 degree slope. So it takes a stepladder to actually get up and into the engine bay to where I can see the old PMD.
It actually looks like I can get the connector off without having to move anything, but the ground wire (on the top between the optical sensor and the shut-off solenoid may be a problem. It's a T-25 screw, and I don't have a straight shot to it because the intake is in the way. I can get a torx bit in it with my screwdriver, but it's not straight, and that thing is in there tight.
Okay, I go in the garage and dig out my 1/4" drive with a bit holder and wobble extension, hoping there will be enough room. While I'm doing this the wind is howling outside, and I heard a loud "crash", like a garbage can being blown over. Our can is chained to the house so I don't pay it any mind.
Get the ratchet and everything I need and walk outside. Hmm... looks like the wind blew the hood closed... Hmmm... why is the hood crooked? Holy bleep! The wind tore the hood off!
Not the whole hood it turned out, but it sheared off the hinge bolt on the driver's side, tore up the plastic vent there, and bent the hinge on the passenger side like a pretzel.
Dug out a new bolt from the bucket on the workbench, bent the hinge back sorta straight, bolted it down and it seems okay.
But I can't get that damn ground wire off the old unit. I'm going to have to pull the intake and I'm outta time. The vet is ten minutes away, appointment is 3:40 PM and it's 3:20 now. Just enough time to find the cat, get her in the carrier and head over there.
All I can say is, the truck better start...
(a few more hours pass by)
Okay, I'm back from the vet (cat needs a different antibiotic for her eye infection) and I have time now to upload and edit the one photo I was able to take today. Not easy balancing on a stepladder, half in an engine bay, with the wind trying to blow the hood off again, and take a picture of something you can barely see, so I'm pleased as heck about how well it actually turned out.
As you can see, there's not much room to work on this. The plug should come off easy enough, there's just enough room to get a thin screwdriver down there and pop the lock loose. I'll have to fish it up with a coathanger, and hope it doesn't get "lost", but it's "do-able". That ground screw, on the other hand, is going to be a real PITA. You can't see it in the photo but it looks like someone put paint or epoxy on it, and I'm concerned that when the screw does break free the epoxy will hold the ring terminal on the wire right to the screw, and it'll try to wrap around the screwdriver, possibly breaking the wire. There's not a heckuvalot of slack in it... I've seriously thought about snipping it with a wire cutter, then crimping on a new terminal, but with my luck that 1/2" will be the 1/2" I need to make it reach the new location. Might do it anyway, and just solder a short extension on it...
(next day)
I may not get to this today, as I planned. To do the job I have to pull the upper intake. I couldn't get a new gasket for it so I was planning on using some black RTV, but the temp outside is currently 28, and I don't know if the RTV will cure at that low a temp.
Supposed to get a few inches of snow tomorrow, so I won't be delivering the load of tile, so the truck can sit a day or two.
(three hours later)
Okay, I put on my woolies and went out to see if I could get this done today. After pulling the plenum, and fighting with that torx head screw for 30 minutes I finally gave up and took it to my buddy at the local truck shop. In the end it finally took a 3/8 drive impact gun to pop that screw free, and we got the whole thing installed and running in just about a half hour. Gave my buddy a few bucks and paid his boss $55 for an hour's labor.
Harvey runs nice now, no more sputter or hesitation.
Since I was changing the PMD I also changed the calibration resistor that controls how big a stroke the solenoid makes at WOT. Went from a #5 resistor to a #9, which will increase the stroke by 4mm. It's not much, but that extra bit of power when getting on the highway will come in handy. It'll take up to 50 start cycles before the ECM actually "sees" the new resistor, and sets the solenoid correctly, so we'll see if I notice any sudden improvement over the next couple of weeks.
Here's the pics of the final installation:
It's a PITA, particularly on cab & chassis trucks because on those the compressor and alternator are reversed, usually it's alt on the driver's side - which gives more working room, and when you throw in a screw that was epoxied down, well, it's not fun.
Well, my new PMD (pump mounted driver) and relocation kit arrived today, but too late to install now. (I hate working by flashlight)
I'll install it tomorrow and take some pictures of the process because I've noticed that there are very few places on the net that actually show how to do it. And mine will be "fun" to do because, unlike every other 6.5l I've found pictures of on the net, the position of my a/c compressor is reversed with the alternator. I'm not sure why this is, but every other photo set I was able to find of how to change the PMD shows the alternator on the driver's side, which leaves just enough room to get to the PMD. With the a/c compressor there though you can't even see the PMD, or the injector pump it's mounted to, which means the intake has to come off to get at it.
(question was asked, "What is a PMD?")
On the 6.5L GM diesel with the DS4 injector pump (after 1994) there are two pumps, the lift pump, which brings fuel up to the fuel filter at about 5-7PSI, and the injector pump, which pressurizes it for the injectors. The injector pump is electronic, and the module that operates it is called the PMD, or pump mounted driver, because it's actually bolted to the side of the pump. It's also sometimes called an FSD, for fuel solenoid driver. The module has two heavy transistors in it that control how the pump works, and those transistors get pretty hot. Some genius at GM figured that if they mounted this to the side of the injector pump the fuel flowing through would keep it cool. Nope, it doesn't. In fact, because the injector pump is mounted in the intake valley, between the two heads, and because GM added a fancy plastic cover to the intake, it's one of the hottest spots in the engine compartment, and these modules have been failing every since. Typically, an OEM PMD will last about 75k (mine went at 77k). There have been some improved PMDs made, that are supposed to handle the higher temps, but I've heard of those failing from the heat as well. In addition, while the intent was to keep the PMD running cooler with the fuel flowing through the pump, no one seems to have thought that the opposite was also true, the PMD heats the fuel. In the winter that's not bad, and actually helps at low temps when diesel can gel, but in the summer, that extra heat can really thin out the diesel, making the pump itself work harder, and with less lubrication, leading to early failure of your $1,400 injector pump.
What most 6.5L owners do then is relocate the PMD to a better spot, and use a proper heatsink to cool it. Many of these bolt to a couple of studs on the intake, raising the PMD up into cooler air (and airflow from the fan), while still being able to reach it with the factory plug. Others have even gone so far as using harness extensions and mounting the unit inside the front bumper, getting out of the engine heat zone altogether.
My new PMD will be mounted to the intake and use the existing plug. While it would run cooler and last longer if I put it outside the engine compartment I dislike the idea of having it where an otherwise mild front collision, that you'd normally be able to drive home from, can crush the PMD and kill the engine. Also, that's less wiring to have to bother with, and less things that could go wrong.
Normally, installing a new PMD this way is a 15 minute job. Just bolt the new one to the intake (it's pre-mounted to the heatsink), pull the plug from the old PMD and plug it in the new one, shift the ground wire over to the new one and you're done. No need to even remove the old PMD from the pump. It's a tight fit reaching the plug though, and you have to fish it out with a coat hanger, but because my compressor is mounted on that side you can't even see where the plug is, so I have to either unbolt the compressor and shift it to the side, or unbolt the upper intake manifold and move it aside to reach the old PMD.
Just to give you a better idea of what I'm talking about I have some photos.
Here's what the injector pump looks like. The PMD is the black box on the side, marked FSD in this picture.
Here's where the pump mounts on a typical 6.5L (this is in a Hummer) The shut-off solenoid is to the left (front of engine) and the fuel solenoid is to the right (rear of engine) which places the PMD at the bottom, down under the radiator hose in the photo.
Now, here's my engine. Note how the condenser line and compressor pretty much block all access to the injector pump and PMD.
(a few hours pass by)
Well that didn't quite work out the way I planned...
I really wish this part had shown up earlier yesterday. Today it's almost 60, sunny, but with 23 MPH winds and gusts of over 40. Yesterday was pretty much the same, but without the wind. You'll see why that's important a little further down...
Okay, so it's 2 PM and I have about an hour and a half to work on the truck before I have to take the cat to her vet appointment. The truck runs well enough to get her there, but this is the only time I have to work on it so...
First, as you might know, the truck does not fit in my garage, which means I have to work on it outside, on a 30 degree slope. So it takes a stepladder to actually get up and into the engine bay to where I can see the old PMD.
It actually looks like I can get the connector off without having to move anything, but the ground wire (on the top between the optical sensor and the shut-off solenoid may be a problem. It's a T-25 screw, and I don't have a straight shot to it because the intake is in the way. I can get a torx bit in it with my screwdriver, but it's not straight, and that thing is in there tight.
Okay, I go in the garage and dig out my 1/4" drive with a bit holder and wobble extension, hoping there will be enough room. While I'm doing this the wind is howling outside, and I heard a loud "crash", like a garbage can being blown over. Our can is chained to the house so I don't pay it any mind.
Get the ratchet and everything I need and walk outside. Hmm... looks like the wind blew the hood closed... Hmmm... why is the hood crooked? Holy bleep! The wind tore the hood off!
Not the whole hood it turned out, but it sheared off the hinge bolt on the driver's side, tore up the plastic vent there, and bent the hinge on the passenger side like a pretzel.
Dug out a new bolt from the bucket on the workbench, bent the hinge back sorta straight, bolted it down and it seems okay.
But I can't get that damn ground wire off the old unit. I'm going to have to pull the intake and I'm outta time. The vet is ten minutes away, appointment is 3:40 PM and it's 3:20 now. Just enough time to find the cat, get her in the carrier and head over there.
All I can say is, the truck better start...
(a few more hours pass by)
Okay, I'm back from the vet (cat needs a different antibiotic for her eye infection) and I have time now to upload and edit the one photo I was able to take today. Not easy balancing on a stepladder, half in an engine bay, with the wind trying to blow the hood off again, and take a picture of something you can barely see, so I'm pleased as heck about how well it actually turned out.
As you can see, there's not much room to work on this. The plug should come off easy enough, there's just enough room to get a thin screwdriver down there and pop the lock loose. I'll have to fish it up with a coathanger, and hope it doesn't get "lost", but it's "do-able". That ground screw, on the other hand, is going to be a real PITA. You can't see it in the photo but it looks like someone put paint or epoxy on it, and I'm concerned that when the screw does break free the epoxy will hold the ring terminal on the wire right to the screw, and it'll try to wrap around the screwdriver, possibly breaking the wire. There's not a heckuvalot of slack in it... I've seriously thought about snipping it with a wire cutter, then crimping on a new terminal, but with my luck that 1/2" will be the 1/2" I need to make it reach the new location. Might do it anyway, and just solder a short extension on it...
(next day)
I may not get to this today, as I planned. To do the job I have to pull the upper intake. I couldn't get a new gasket for it so I was planning on using some black RTV, but the temp outside is currently 28, and I don't know if the RTV will cure at that low a temp.
Supposed to get a few inches of snow tomorrow, so I won't be delivering the load of tile, so the truck can sit a day or two.
(three hours later)
Okay, I put on my woolies and went out to see if I could get this done today. After pulling the plenum, and fighting with that torx head screw for 30 minutes I finally gave up and took it to my buddy at the local truck shop. In the end it finally took a 3/8 drive impact gun to pop that screw free, and we got the whole thing installed and running in just about a half hour. Gave my buddy a few bucks and paid his boss $55 for an hour's labor.
Harvey runs nice now, no more sputter or hesitation.
Since I was changing the PMD I also changed the calibration resistor that controls how big a stroke the solenoid makes at WOT. Went from a #5 resistor to a #9, which will increase the stroke by 4mm. It's not much, but that extra bit of power when getting on the highway will come in handy. It'll take up to 50 start cycles before the ECM actually "sees" the new resistor, and sets the solenoid correctly, so we'll see if I notice any sudden improvement over the next couple of weeks.
Here's the pics of the final installation:
It's a PITA, particularly on cab & chassis trucks because on those the compressor and alternator are reversed, usually it's alt on the driver's side - which gives more working room, and when you throw in a screw that was epoxied down, well, it's not fun.
