My boss has two 6.5 i believe. 94-96 i think. just work trucks but the one constantly shuts off while driving. a number of mechanics have replaced some module. ( is this the pmd? what is it?) im fairly ignorant when i go away from cummins so i want to learn. and the other isnt as bad but wont start sometimes and shuts off once in a blue moon. Love to help him fix it so give me all the info you got.

 

Could the PMD, look on the drivers side of the IP, if there is a black box on the side if it, it needs to be moved to a cooler place and maybe even replaced now, that is the brain of the pump, it gets hot there and goes bad. You can get a kit that will have a longer wire harness to move it to say behind the front bumper where it will be cooler. This would be where I would start...........

 

After some more reading this is what i considered. Is their one that is better than the other or are all the brands the same?

 

I do know that there is a blue and a black PMD, as for the better of the two, I don't know, my trucks are manual pumps. Maybe someone else will chim in.

 

heat sync and FSD Cooler are the best on the market.

get a 6' extension cable and mount it away from the engine compartment

 

yep I just got my kit in friday from a place in fl that somone told me about on this site.. but make sure when u order that you look at the wireing harness if you dont get a new one.. some have half moon shaped plugs and some do not.. so i had to order a new wireing harnes just now..

 

okay thanks alot.

If the pmd burns up can the pump be harmed?

 

not that ive heard of it just will just get to the point to where it wont even start

 

The Pump Mounted Driver (PMD) is a known failure point on the 6.x engines.

It simply drives the fuel solenoid in response to the Power Control Module (PCM or ECM if you prefer) commands and sends feed back to the PCM that the commanded event has occurred.

It's really just a slave module, it doesn't do any calculations or "thinking".

The PCM determines the timing of the injection and the pulse width and the PMD executes it via the Fuel Solenoid on the pump.

If it has a total failure, it can't hurt the IP. It just stops opening and closing the Fuel solenoid. The real problem is when they start breaking down it causes all kind of problems that can make you scratch your head.

For example, you can get a torque convertor lock up code with a failing PMD. Sounds weird right? Lets look at what's happening;

The PMD is breaking down and doesn't respond properly (or at all) to the PCM but it's a partial fail and the truck still runs. PMDs are funny beasts that way, they can have partial or total failures. The engine will "miss" or may "kick" with an improperly timed or missed injection event, but it is one or two events in an engine running around 2200 rpm. You don't feel it in the cab. But the drivetrain feels it. The torque convertor slips a little bit because it's a relatively small clutch surface and can't handle the "kick". The PCM sees the slippage (what the PCM monitors, it monitors VERY closely) and locks the drivetrain into limp mode to try and protect the transmission and convertor. You end up driving home locked in second gear. You pull the codes and see torque convertor slippage but no PMD code (you have to figure it out). So you get a new convertor or maybe a trans rebuild. Start 'er up and same problem. All from a failing PMD....

Don't pshaw. It happened to me (well, not the trans rebuild, I changed my PMD and all was good again). PMD started to fail but would run, kept kicking the PCM into limp mode.

Most of the new PMDs available these days are the "upgraded" design, whether it comes from Flight Systems (aftermarket supplier, sometimes marked "DTech") or Stanadyne (original manufacturer). Identifiable by a thicker body on the module. Some of the upgrades in the module itself are different circuit traces, different potting compound and improved components to better deal with the temperature swings.

The original PMD was mounted on the IP and the idea was to use the fuel to cool it. This was a sound idea, at least it was while the engine was running.

The problem was when the engine is shut down, the fuel flow stops then the module is baked in radiant engine heat as the IP is in the "V" of the engine. This would heat the PMD outside it's design specs.

It survives it for a while, but eventually starts to break down from the thermal stress.

Especially when you consider most people drive it to the store, shut it down, it heat soaks outside it's operation specs, then they come back to the truck after picking up a pack of smokes and start it up to drive home. This results in the PMD operating outside specs and it eventually fails. Usually prematurely.

If your employer wants to stop fragging PMDs, point him towards Heath Diesel. They sell the upgraded module on a large heat sink that mounts outside the engine compartment. They give you a 7 year warranty so they stand by the product.

Trivia: It's a PMD while pump mounted, once remote mounted it's more accurately called a FSD (or fuel solenoid driver) although most 6.5-ers will give you funny look if you call it that.

I've got a Heath one on my truck. Stopped my PMD problems dead in their tracks. Been running for a year now. Worth the little bit extra money for a 7 year replacement warranty. Heath says he has PMDs that have been running for over 10 years on the same truck. That seems to indicate they have a good handle on the cure. Take with a grain of salt maybe? I believe him....

On another note, stay away from the designs that mount the PMD on a heat sink on the intake manifold (or anywhere else in the engine bay). They have the same issues as mounting the PMD on the IP.

You need to get it out of the engine bay so there's a large temp delta between the heat sink and ambient. The heat sink doesn't need to be finned, but it needs to have a large mass to absorb and reject the heat. This is what strips the heat away from the PMD and makes it live.....

Good luck.

 

Awesome post!!! Thanks alot