Switching pcms

Discussion in 'Electronics Q&A' started by Coz, Jul 11, 2020.

  1. Coz

    Coz Member

    249
    Oct 9, 2018
    2008 Sundancer 310
    Merc Mag 350 DTS w/Bravo III
    I’m trying to troubleshoot a problem with one of my engines. Have another thread on the issue so not gonna rehash the details. But, is there any reason I couldn’t swap pcms temporarily to see if the problem follows?

    I have 08 mag 350s mpi with dts and pcms-555s.
     
  2. Henry Boyd

    Henry Boyd Well-Known Member GOLD Sponsor

    Apr 24, 2007
    Newburyport, on the peaceful and serene Merrimack
    ‘09 Sabre 38 Hardtop Express “Serenity”
    Volvo D6 w/IPS450 Pods
    Personally I wouldn’t. One of our members swapped a PCM off a good engine to test out an engine that was immobilized. That toasted the good one and then he was down two at $1500.00 each. It was a bad iac valve.
     
  3. Ididntdoit

    Ididntdoit Well-Known Member

    Dec 5, 2007
    New England & South Florida
    1976 17 Sport
    90hp Etec
    ya - then as a moderator he erased the thread so he could commit insurance fraud
     
  4. Henry Boyd

    Henry Boyd Well-Known Member GOLD Sponsor

    Apr 24, 2007
    Newburyport, on the peaceful and serene Merrimack
    ‘09 Sabre 38 Hardtop Express “Serenity”
    Volvo D6 w/IPS450 Pods
    Ididntknowthat
     
  5. Coz

    Coz Member

    249
    Oct 9, 2018
    2008 Sundancer 310
    Merc Mag 350 DTS w/Bravo III
    I called Merc and they said on a mechanical throttle engine you can swap pcms no issues. On DTS the dealer has to reassign the pcm to the helm controls, so only the dealer can do it.

    Now why didn’t the dealer tell me that!
     
  6. Henry Boyd

    Henry Boyd Well-Known Member GOLD Sponsor

    Apr 24, 2007
    Newburyport, on the peaceful and serene Merrimack
    ‘09 Sabre 38 Hardtop Express “Serenity”
    Volvo D6 w/IPS450 Pods
    that’s not quite the answer to the question. Can you swap them to test if one is not working? Yes, you can swap them on a non-DTS engine. They are interchangeable. The real question is, “Would you want to swap a good $1500 electronic part to another engine to test if that engine destroyed its original part?” Seems to me either way the answer should be, “Are you daft? You want find out if the engine fried the PCM, by experimenting with your last remaining good one?”
     
    Last edited: Jul 15, 2020
  7. Coz

    Coz Member

    249
    Oct 9, 2018
    2008 Sundancer 310
    Merc Mag 350 DTS w/Bravo III
    I would agree Henry, but for the record, that wasn't my question. Both of my pcms work, 1 just may not be programmed the same as the other.
     
  8. Henry Boyd

    Henry Boyd Well-Known Member GOLD Sponsor

    Apr 24, 2007
    Newburyport, on the peaceful and serene Merrimack
    ‘09 Sabre 38 Hardtop Express “Serenity”
    Volvo D6 w/IPS450 Pods
    More back story! Seriously, this highlights an interesting discussion that often comes up in car forums;”do you need to buy a Rinda/PIWIS/insert name here/ diagnostic tool?”
     
  9. Coz

    Coz Member

    249
    Oct 9, 2018
    2008 Sundancer 310
    Merc Mag 350 DTS w/Bravo III
    I have a rinda scanner and complete set of service manuals.
     
    scoflaw likes this.
  10. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Then there should be no reason whatsoever that you would need to switch PCM's.
     
  11. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    So are they programmed identically?
     
  12. Coz

    Coz Member

    249
    Oct 9, 2018
    2008 Sundancer 310
    Merc Mag 350 DTS w/Bravo III
    Scanner doesn’t show any programming. Basically just shows sensor status, fault codes and allows some output tests. Only dealers can see the map.

    The purpose of this thread was to see if swapping pcms was a viable troubleshooting option. In my case I have other things to try first (as scoflaw has suggested elsewhere).
     
  13. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    You want to compare sensor values between the 2 engines not mapping. just basic stuff. Scroll thru the menu and see if they are close between the 2
     
    techmitch likes this.

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