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502 mag mpi rough idle after one dual battery clamp snapped putting hole in it

Old 07-20-2020, 09:51 AM
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Default 502 mag mpi rough idle after one dual battery clamp snapped putting hole in it

Just bought my 2nd 22 donzi classic with a 502mag mpi.. still have my 18. Boat ran beautiful, was never in rough water before..

I filled it with 93 the first day and 2nd day had to put 89 in it.but it ran fine until the battery issue..

I went by the inlet and one of the first hard hits I heard something whining.. lifted the hatch and the one battery was in the bilge with a hole in the side from rubbing on a pulley. The battery bracket had snapped. I disconnected it whole runningarunning tied it down and idled back to dock. the engine idle was erratic.

I'm not sure why but the batteries are setup to only start on both? It won't start on 1 or 2 (I may be wrong but I know it won't start on 1 never tried 2) is there a reason for this? I'm wondering if the second battery gives the ignition more juice? I doubt it? Once at the dock I shut her off gave the marina the bad battery and then checked to see if it would start and it did.. with switch on both..

What would cause the sudden erratic idle and the boat is def down on power it won't rev past 4500? And normally hits 5200.. maybe something else happened and the battery masked the issue? It def sounds like it misfiring for sure. And feel like it should run fine on one battery but maybe there is some sort of mod to run on two to boost power?

Help!

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Old 07-20-2020, 10:07 AM
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Ha nevermind about the misfire... One of the plug wires was loose...

However does any know why the boat would be purposely setup to only start on both? Sounds like it's not wired right unless there is a reason?
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Old 07-20-2020, 10:29 AM
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Originally Posted by beerock View Post
Ha nevermind about the misfire... One of the plug wires was loose...

However does any know why the boat would be purposely setup to only start on both? Sounds like it's not wired right unless there is a reason?
No, no clue why must start on both. Check other battery to see if itís good. Also Check itís wiring to ground and utís wiring to the switch.

Sometimes people wire things like batteries to hiw they want it vs how orhers want it. And Sometimes people donít know what the fk they are doing.
lololol
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Old 07-20-2020, 10:32 AM
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is your battery selector arc'd or just wired improperly? They are a "make before break" switch so you should have continuity from "Batt 1" as it switches to "BOTH" 1&2... then it breaks "Batt 1" as the selector goes to select "batt 2" and vice versa

Rather simple to wire.....




Last edited by speicher lane; 07-20-2020 at 10:35 AM.
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Old 07-20-2020, 10:35 AM
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Usually a boat that will only start on "all" position on the switch then it means 1 or both batteries are weak or 1 is dead. Try putting switch on 1 and then 2 and run the trim up and down on each one. If trim is slow on one position then its a battery. also make sure Both batteries have a ground wire that goes to the engine block.. 1 ground to block and a ground jumper from one battery to the other is not acceptable but is done frequently

Chris.
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