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Thread: PMD problems

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  1. #1
    Join Date
    Mar 2007
    Location
    Tallassee. Al
    Posts
    5

    Unhappy PMD problems

    I have a 1995 c2500 6.5L. I have replaced the PMD 3 times in the past 3 years. Is there another solution for this part? It is very expensive.

    James

  2. #2
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    The best solution we have to date is to mount the PMD on a good remote mounted cooler outside of the engine bay.
    Extention cables available from various aftermarket sources up to 6 ft long.

    Dtech now offers a replacement PMD for a fairly decent price. I paid $279 for mine IIRC
    I installed one of these on my 95 DaHooooley earlier this fall when I was having some issues with it. Turned out to be another little problem but there were no codes and anytime the engine cuts out the PMD can be a suspect as far as Im concerned, at least when other obvious things are eliminated first.

    The DTECH PMD looks just like a factory unit except it is a little thicker.
    The key is remote mount it where it stays cool/Cooler than under the hood..

    Another issue can possibly be poor grounds on the battery cables as well as the psitive cables too. An alternator thats starting to toss alternating current rather than DC can louse things up too.
    Be sure your engine and body grounds at the rear of the engine Intake manifold RH side are clean and tight.

    14v+ should be seen at the power box feed with the engine idleing.

    The sensitive micro electronics on these trucks needs to see good clean voltage.
    If the cables are going south and the voltage is dropping off then the amperage draws can climb. If there are ground issues this can seriously effect the electronics as when the grounds go sour all sorts of wierd crap can happen including damaging sensitive circuits.

    Another seldom taked about subject is that whenever a rig has some welding done on it, such as a hitch or ???? the batteries should be disconnected.

    Check these things out as well as remote your PMD

    Hope this answers your ?????????

    Happy Hollidays

    Robyn
    Last edited by Robyn; 12-24-2007 at 08:09. Reason: addition
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  3. #3
    Join Date
    Apr 2003
    Location
    Hendersonville, TN
    Posts
    22

    Default More PMD Thoughts

    This subject always stirs up comment...

    I bought a 4-foot extension with finned cooler, removed the cover over the power transistors, used Bellville-spring washers (supplied by that vendor) to mount PMD to cooler, used the supplied heat-transfer goop, and moved the PMD to the bracket with the ABS controller on it--handy threaded holes there . Then I had another failure . This time I moved the whole thing to the hole in front of the driver-side battery, and mounted a fan in front of it.

    To date, no failures!

    Info on the fan: Radio Shack item #002763154, 120x25 mm...still running at last check. It was a trial to check life, because this is quite a bit more severe duty than sitting in a case on the floor of the house! I have the fan running at high speed (it's adjustable) whenever the ignition is on.

    Good points, Robyn, on the voltage, and on welding. I would go a notch more conservative on welding issues, though, because in my former life as a maintenance manager, I saw some suspicious things happen on equipment on which we welded. The stray and induced currents on the structure being welded aren't at all predictable, and damage can occur which goes undetected while allowing function of the part, but later causes a "mysterious" failure. So I would unplug the PMD when welding is being done...come to think of it, maybe one of MY failures happened after I welded up my 4" exhaust!!!

    Also, get rid of the side-post batteries...they will at some point, if you keep the truck long enough, seep acid through the internal seal and make your connectors disappear while never showing any problem outside the little plastic cover. (It's nice to be able to make a firm connection if you want to jump another vehicle from...or TO...yours.)

    AND...don't forget to remove the %*&$^*@ TURBO POWER plastic cover, even if you also move the PMD. Trapping the heat and inhibiting air movement ANYWHERE around the injection pump can't be good for the fuel-supplied lubrication of the injection pump. (Not to mention its former duty in trapping heat to help roast the PMD!?!?!?)

    ¡Buena suerte! Good luck!

  4. #4
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    YUPPPPPPPPPP as far from the heavy heat as is possible.

    The PMD is not nearly as vulnerable to the stray currents as is the Computer/ ECM-PCM

    Disconnecting the battery cables will "Usually" stop any issues as there is not a completed path for the flow of these stray voltages.

    If the gounds are not connected then in theory there would be no path for the influx of current.

    The class 8 trucks have stickers all over them as to this very subject due to the many and varied upfits this stuff sees when being outfited to do specific jobs (Dump trucks, cranes ect)


    The removal of heat from the PMD is the one proven thing that does enhance the little black box's life span.

    I am very excited to now see that there is another player in the PMD arena.
    With Dtech making a replacement we at least have a somewhat lesser expensive choice.
    I am running one now so we shall see.

    I run the dual post Optima jello batteries and have had very good luck with them to date on all my rigs.

    The big truck gets top threaded terminal commercial batteries and they are ok.

    Yup the cables just go away inside and still look great

    Been mugged there a few times earlier in my life.


    best
    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  5. #5
    Join Date
    Jun 2005
    Location
    Alberta, Canada
    Posts
    36

    Default

    Personally, I figure if your truck has eaten 3 PMDs in 3 years, you should be thinking about buying one with a warranty.

    The Heath PMD Isolator (reviewed on this forum) has a 7-yr warranty and mounts outside the engine bay.

    Half of the issues with home-brew solutions include wiring, flat surfacing on the heat-sinks, improper thermal transfer application, poor electrical work or grounding issues, and finally not doing the calculations on mass/suirface area of the heat sink for thermal balance.

    Why tell somebody that's already bought 3 PMDs to try again?

    It's not like the worst that will happen is it might not start... stalling in traffic with a load on is scary (steering/brakes/hydroboost), or when merging, or just plain dying out in the boonies somewhere (it IS winter, ya know). Peace of mind is priceless.

    Phone Heath Diesel or USDieselparts and solve your problem for 7 years.

    JMHO
    Real Trucks Don\'t Have Spark Plugs

  6. #6
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    I have seen several failures of electrical stuff after rigs have been to the exhaust shops.

    All it takes is a little wild and wooly fluxing of current induced into some little electronic component to set the failure in motion.

    An old friend of mine installed hitches for years and did a job on a Reeeeeeeeeealy high $$$$ Mercedes and after he finished the hitch the rig would not run

    He called me and I advised him to disconnect ther batteries and wait about 10 minutes and then hook it back up.
    Seems that the Mercedes has some sort of circuit protection system????

    It ran fine afterwards and the rig was a local one.

    Enough to make one shudder though at the thought.

    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

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