View Full Version : 6.5 chevy

12-07-2011, 08:12 PM
i own a 97 chevy dump 3500 6.5 D with 49k, 4x4., etc. it recently was in the shop with a check engine light. the truck seemed to hold back when accelerating then it seemed like a valve opened up? then it ran fine. the code read turbo boost selenoid which was replaced. it has done it since once but still doesnt feel the same.

12-07-2011, 08:20 PM
i own a 97 chevy dump 3500 6.5 D with 49k, 4x4., etc. it recently was in the shop with a check engine light. the truck seemed to hold back when accelerating then it seemed like a valve opened up? then it ran fine. the code read turbo boost selenoid which was replaced. it has done it since once but still doesnt feel the same.

PMD? Have you replaced and relocated your PMD? www.dieselplace.com has a huge 6.5L section over there.

12-08-2011, 06:37 PM
would that affect the power i thought it controlled the injector pump

12-08-2011, 08:45 PM
pmd? whats that. i ahve the same issue with mine

12-09-2011, 12:27 AM
would that affect the power i thought it controlled the injector pump
It's the brains of the Injection Pump, telling it when to fire fuel into the cyclinders.

This is from dieselplace.com there write up is the best I can find and I don't have that amount of time.
- What’s the PMD/FSD I keep reading about? What’s it do, and why should I “relocate” it?

There are countless FSD related threads right here in the 6.5 forum so it’s very worthwhile searching for the term “PMD” in the 6.5 forum to read up on the potential issues, even if you aren’t (yet) experiencing any yourself, but here’s the basics.

If you have a 6.5 with an electronic DS4 Injection pump (1994 and newer), you have a FSD. They commonly fail due to their location (and heat) resulting in stalling, hesitation, and eventual stranding.

The DS4 injection pump, like the 6.5 itself earned a much maligned reputation for being “Junk”. Although in it’s early years it did have some problems (which are covered under an 11 year extended warranty by GM) in many cases the Injection Pump’s bad reputation came as a result of failed FSD units, not the pump itself. Unfortunately, for those who took their vehicles back to GM and found themselves out of warranty coverage, it was likely a very expensive experience.

Worse yet, many mechanics with little to no diesel (or 6.5) experience automatically fingered the entire injection pump (at a replacement cost of >$1000) when in reality the pump itself was fine, but only the (much less costly) FSD unit had failed!

The FSD (Fuel supply driver) is more commonly referred to here at the Diesel Place forum as the “PMD”, or “Pump mounted driver”. It’s a small black box, about the size of a deck of cards mounted on the front of the injection pump. The injection pump itself is located under the intake manifold, which in turn is located under the “Turbo Power” plastic trim piece on top of the engine.

Assuming the PMD is in it’s stock location it’s a bit out of the way, but You CAN see the it if you look closely between the arms of the intake manifold - once you the plastic “Turbo Power” cover off (which you may want to throw away, all it does is block heat from escaping!) you will be able to see it if you look closely with a flashlight - you may see the words “Stanadyne” printed on the front of the module and there will be a single wiring harness plugged into it.

Don’t be surprised to see that the previous owner has already moved the PMD - you may find it (on an extension cord) mounted on the intake manifold, or (ideally) out of the engine compartment completely. If you see the PMD module in it’s stock location but nothing appears to be plugged into it, it’s been relocated already - follow the nearby cord and you should find it, if it’s not already completely obvious.

The PMD module is the brain that tells the injection pump when to fire fuel into the cylinders. Without it, your truck won’t run, and when it begins to fail the problems can range from hesitation, to random stalls (usually when hot), to complete no-start situations.

This module, when mounted in it’s stock location, fails all too frequently. Far too many 6.5 owners have suffered the fate of a failed PMD, and if you take it to a repair facility you can end up paying $500 or more to get it fixed. It need not be that expensive, and putting a new module back in it’s stock location (which is what many shops will do!) is only asking to experience the same failure again within a year or two, often less.

Why does it fail? HEAT. Although GM’s plan was for the injection pump itself to act as a heat-sink (and the fuel flowing through it to cool it further) the simple reality is that it didn’t work - this area was too hot and simply cooks the module, especially when you shut your engine off after driving and it gets heat soaked. Heat is a killer of the PMD!

So, if you just bought a 6.5 equipped vehicle and discover the PMD is still in it’s stock location .....you really should relocate it. Look at the supporting vendors here and you will find lots of “Remote mount PMD kits” available. You will need an extension harness, a PMD cooler (ESSENTIAL!) and if you are experiencing the symptoms of a failed PMD, a new PMD itself. You can get ALL of this (Cooler, wiring, and replacement PMD) for somewhere in the $500 rane, so don’t get sucked into paying $500+ at a dealer or diesel shop for a stock replacement PM alone which won’t include a cooler or extension cable.

We appreciate it if you make your purchase from one of our supporting vendors, as mentioned - remember, our vendors are what keeps Diesel Place free for you and I!

Simply visit this forum (click) to find a vendor that stocks the PMD kit. It's easy!

So... Ideally, you want to get the whole PMD assembly out of the engine compartment - some kits are designed to be mounted on the intake manifold or elsewhere under the hood, and although this is *better* then the stock location, it is still not perfect - I myself had a cooler mounted on the intake manifold and it cooked after 3 years, almost stranding me in the process.

Many people mount them behind the front bumper (in one of the “nostrils), or beside the oil cooler in front of the grille itself. The module is weatherproof (as is the connector) so you can mount it almost anywhere that it will get good airflow and be protected from impact damage.

A cooler attached directly to the PMD is ESSENTIAL! The PMD itself generates a lot of heat and testing has shown that a PMD operated without a heat sink will cook itself in less then 5 minutes, so simply danging it by it’s wire or zip-tying it in a good airflow area will not work. A good heat sink will take the heat generated and dissipate it to air - obviously this means the PMD and cooler need to be located in an area with adequate airflow to begin with, hence the bumper or grille locations.

When mounting the PMD to a cooler it’s also essential that a good heat-transfer paste be used - this is easily available at any computer store (and is typically included with many PMD cooler kits) - it’s function is to aid the transfer of heat from the module to the cooler. Without it, heat transfer will not be ideal and you may shorten the lifespan of the PMD.

The key is that ANYWHERE else is better then the stock location. Buy the longest extension cord you can (or solder your own!) and mount it somewhere else...ANYWHERE else than the stock location. Your PMD (and wallet) will thank you, and you probably will never have to worry about PMD failure (and being stranded) ever again.

And lastly, a spare PMD in your glove box is always a wise idea for a 6.5 owner, especially if you tow or travel long distances. A $50 “used but tested good” one from eBay is a worthwhile investment as a spare - it could rescue you in a pinch!

So, the moral of the story? If you just got a new 6.5 and the PMD is in the stock location, relocate it. Most people opt to just buy a second PMD and leave the factory one in it’s current location - removing it requires removal of the intake manifold and is often more hassle then it’s worth, especially when all you’re going to do is throw it in the garbage anyways. Yes, it’s a few hundred dollars of investment, but ask yourself if being stranded in the middle of the night (or on a deserted road) plus the cost of the tow-truck is worth the savings. If your PMD is in it’s stock location it WILL eventually cause you grief - head it off at the pass!

Without doubt the PMD (and it’s related issues) generate the most posts in the Diesel Place 6.5 forum, so before making a new post on the subject be SURE to do a search for “PMD” and read about the issue. Of course, if you need help, make a new post - we’re a friendly bunch and will be glad to help diagnose your issue.