PMD or Not?

[trbankii]

Another post questioning what replacement PMD was currently being recommended compared to other posts about converting the electronic injection over to mechanical injection led me to the question of what real advantages there were for using a PMD over mechanical injection?

I’m guessing that it is similar to the decisions for EFI over carburetors? That you have better control of engine parameters over the full range of operation?

Obviously, OEMs did it to meet mileage and emission requirements. But would people say that there were significant benefits from the “early” setups like that found on the 6.5?

Just curious...

[Kennedy]

We use the Stanadyne gray PMD pretty much exclusively. I think that I have 9 of 10 Dtech PMD's still sitting here since I ordered years back. probably should sell them some day I guess.

the mechanical pumps wear out the housing and in some cases head and rotor. They don't seem to go much past 100,000 miles without serious degradation. The DS4 seems to last a lot longer so long as the electronics live. The electronics can put the fuel in when they want. The mechanicals are tied to old governor weight principles.

[Robyn]

My feeling after owning both is a simple one.

When the DS4 system is working the way it's supposed to it is great.
The driveability is smooth throughout the entire range.

The rub comes when it starts giving trouble.

The mechanical system is, IMHO more reliable when it counts.

I agree with John that the DB2 is a 100k unit and then only with diligent maintenance of the filters.

The DS4 system was rushed into service for the 94 model year and still had issues that should have been dealt with prior to releasing it to the consumer.

The idea and concept were reasonable, just the realization was effed up, and sadly it ended there with little improvement by GM or Stanadyne throughout the production years.

With the 6.5 electronic in production for 7 years you would think the entire bag of problems could have been sorted out completely, but sadly it was not.


My choice would be a mechanical IP, but the issues of a good tranny controller for the 4L80 were never great.


With a stick shift it's a no brainer.

[trbankii]

Hmmm… I bought mine with more than 100K on the clock, but I seriously doubt that the IP was replaced before I bought it. I sort of question the maintenance it got (fuel filters) as well. So that sounds like something I should be looking at now that it has close to twice that on the clock.

[Kennedy]

I'll add this: It is very seldom that we ever hear of either system leaving a guy stranded by the side of the road. Assuming properly maintained and not neglected of course.

I do hear from DS owners that have dead trucks, but that is typically after ignoring the symptoms for weeks, months, even years.

[trbankii]

I just took a look at the IPs on your page, John, and saw this - “One of the classic symptoms of a failing 4911 pump is hot no-starts. The truck will sometimes start if the glow plugs are forced on, and will typically start right up when cooled down.”

I had that twice last summer. Was able to pour water on the glow plug controller to “trick” it to cycle the plugs and was on my way again.

[Robyn]

I have had several PMD failures that left me stuck.

The first was on a brand new (then) 95 Burb with less the a K on the clock

Towed to dealer and a new IP installed.

At 20K on the clock, same thing, then again about 50K.

After the learning curve I just carried a spare with a couple tools to swap the beast when it quit.

I have had them just up and die, boom plop done DEAD

Also had them stall, restart and go again for a while.

The fun ones are the Galloping goose around the parking lot with the engine howling and black smoke rolling :eek: