Switching pcms

C

Coz

Active Member
Oct 9, 2018
443
Boat Info
2008 Sundancer 310
Engines
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.
 
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.
 
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!
 
Coz said:
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!
Click to expand...

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:
Henry Boyd said:
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 remains good one?”
Click to expand...

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.
 
Coz said:
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.
Click to expand...

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?”
 
I have a rinda scanner and complete set of service manuals.
 
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).
 
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
 
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