Challenger 1800 Intermittent Motors Cut Out (Electrical)

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teamgreen737

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Hey guys, I've had these twin 787 challengers for quite a few years now and have done everything including bottom up rebuilds on both 787's and fixing or replacing almost every component on this boat throughout the years owning. I'm pretty sure I have the shop manual memorized by this time with the Challenger 1800.

This is a new problem that has started a few weeks back that is absolutely driving me crazy which has been very difficult to figure out. First three outings this year were flawless per usual, as it should be on a boat with fairly fresh motors who's carbs are rebuilt every year. Three outings ago, both motors suddenly shut off as if my knee bumped the key off the DESS post. They quickly restarted and I was on my way, only for it to happen again. By the end of this outing the twin motors had randomly shut down over 8 times. Each time they fire back up instantly (not a fuel issue). There is no rhyme or reason to this electrical shut down of both motors, no similar RPM, no big wave or bump, and no specific condition that I can relate to this happening.

I researched the forums and found that the DESS key post was most like the culprit so I pulled my post off my other challenger 1800 that works perfectly and ordered another off of ebay. Installed each of these and have still run into the problem of random shut downs. I've cleaned the key contacts very well (this is a fresh water boat and they were already clean) and have checked connections from the DESS post to the electrical box in back. My second last outing I ran the boat for 3+ hours without a single issue. Yesterday I went to take it out thinking I had fixed the problem and experienced the random shut downs once again.

Does anyone have any other ideas to check regarding this problem? Do you think I have a faulty ECM that is randomly shutting down signals to both motors??! Anyway to check or diagnosis this?
 
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It’s really difficult to diagnose intermittent problems with the MPEM like that... Is it shutting down at different throttle settings, or does it only seem to do it when you’re wide open?
 
Different throttle settings... Idle, barely going, wide open... Haven't noticed it do it in neutral but definitely while in drive. Random with no rhyme or reason.

5 outings ago: No problem
4 outings ago: random shut downs of both motors
***CHANGED DESS POST***
***Cleaned and retightened both of my battery posts and connectors
***Checked 5 amp MPEM fuse along with others (switched good 5 amp MPEM fuse out with another just in case)
3 outings ago: no problems
2 outings ago: no problems
Last Outing: motors both randomly shutting down together.
 
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Interesting problem. sounds to me like it’s the battery and it’s connection. If MPEM looses power it shuts off motors. If both are cutting out there are only a few things that can do that. Most likely things controlled by the MPEM. So that leaves DESS or power of MPEM itself. Or the dreaded possibility of a failing MPEM. Ignoring the last as there is no fix or test. You replaced the dess post with no improvement but it may actually be a failing key. That requires a dealer or someone with candoopro to program the MPEM to a new key.

I would spend some time to be sure all power and ground connections are solid both at battery and in electronic box
 
I agree with you Doug. I will be having a new key programmed, removing all battery connections once again to check end connectors and again in the MPEM box.

This boat also has a Perko switch for dual batteries. I will be removing and replacing this- you never know.

Will keep you posted.
 
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