carbed 1996 4.3 merc won't shut off with key- fuel pump runs continously

matth121

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May 19, 2011
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hey guys, having some issues bringing this engine back to life. Heres the background info- engine was partially submerged in rain water due to plug being left in and battery removed(this isn't my boat, a friends). I replaced the up trim solenoid for him last year but never got a chance to do much more to it. now, after replacing the starter, the boat started on muffs fairly easily and ran at idle without an issue(except that the alternator isnt charging and needs to be replaced). after getting it up to temp and ensuring no leaks and everything looked good- decided to turn it off. keyswitch off- dash lights and radio turn off but engine keeps running- not dieseling- running. another issue and possibly the cause is that the fuel pump runs continuously when battery is connected. after reading as many posts related to fuel pump issues as i could handle- this is what i think i know- no relays since its carbed not efi so a stuck relay isnt the cause. the purple w/ wht wire runs from the starter solenoid to the fuel pump as it should and this is where it should be getting power from but only when cranked. The issue was present with the old starter in place. I'd love to hear your thoughts on what to try next or what may be the cause. i wish i could provide serial numbers but the boats about an hours drive from me and theres not even any cell coverage out there. Not sure what else i can tell you. its an alpha one drive. thanks for any help you can offer
 

alldodge

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hey guys, having some issues bringing this engine back to life. Heres the background info- engine was partially submerged in rain water due to plug being left in and battery removed(this isn't my boat, a friends). I replaced the up trim solenoid for him last year but never got a chance to do much more to it. now, after replacing the starter, the boat started on muffs fairly easily and ran at idle without an issue(except that the alternator isnt charging and needs to be replaced). after getting it up to temp and ensuring no leaks and everything looked good- decided to turn it off. keyswitch off- dash lights and radio turn off but engine keeps running- not dieseling- running. another issue and possibly the cause is that the fuel pump runs continuously when battery is connected. after reading as many posts related to fuel pump issues as i could handle- this is what i think i know- no relays since its carbed not efi so a stuck relay isnt the cause. the purple w/ wht wire runs from the starter solenoid to the fuel pump as it should and this is where it should be getting power from but only when cranked. The issue was present with the old starter in place. I'd love to hear your thoughts on what to try next or what may be the cause. i wish i could provide serial numbers but the boats about an hours drive from me and theres not even any cell coverage out there. Not sure what else i can tell you. its an alpha one drive. thanks for any help you can offer

You have something which is applying power to the purple wire circuit and is not actuated by the key. The engine would die even if the fuel pump did not if power was removed from the coil. This isn't happening. Check out the pic below of the typical wiring setup
 

keith2k455

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Jul 23, 2012
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Does fuel pump run all the time the battery is connected? Even before boat is started with the key off?
 

matth121

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May 19, 2011
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275
all the time- as soon as battery is connected. no pic in your post AllDodge- thanks for the help guys
 

alldodge

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all the time- as soon as battery is connected. no pic in your post AllDodge- thanks for the help guys

Pic posting has issues (iboats) :facepalm: but should be there now. Your purple wire should only be hot when the key is turned, need to check your wiring
 

matth121

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Patiently waiting for that pic, lol. PM it maybe? Fuel pump issue asside, any thoughts on why my ignition would remain on after key turned off/removed from ignition?
check the wiring i guess eh
 

Bt Doctur

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UntitledW5_zps2e6e5ed9.jpg
 

Bt Doctur

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If you can follow this, the purple wire provides the 12v from the ign switch to turn on the alt. the orange to the alt comes from the battery. alt have been known to backfeed the circuit.
 

matth121

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i can for sure confirm that the orange is connected to battery via the positive post on starter solenoid. by backfeeding the circuit- do you think thats why my ignition remains on? also, the alt isnt charging since the only way im able to kill the motor at this point is it remove the battery cable. Thanks for the pic
 

Bt Doctur

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remove all the wire from the alt , and retest. motor should start and stop with the key
 

matth121

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May 19, 2011
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so i'll be heading out to try the alternator later but have a question about the fuel pump issue. from what i understand- the pump should come on for about 2 seconds when key is turned and will get power from the starter solenoid from the purple/yellow wire then an oil pressure switch closes to confirm oil pressure and allows pump to run. since mine runs continuously once battery is connected, is it possible the oil pressure switch is stuck closed? Thanks for any advice
 

JustJason

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Aug 27, 2007
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5,321
Disconnect your alternator completely and retry it. If the voltage regulator is shorted it can backfeed 12V through the sense wire, and keep your ignition and fuel pump powered up.
 

Bt Doctur

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~~so i'll be heading out to try the alternator later but have a question about the fuel pump issue. from what i understand- the pump should come on for about 2 seconds when key is turned

That only applies to fuel injected motors. Yours is powered by the solenoid in :start " position until there is oil pressure, then in "run" position the pump is powered
by the ign circuit
 

matth121

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May 19, 2011
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ok, my bad. so when i replaced the starter, as i was tightening the purp/yel wire, the ring terminal twisted and came in contact with the positive terminal of the solenoid. I realized this only after disconnecting all alt wires and having the exact same issue. fixed now. thanks for all the help. have a few more issues but i think a new thread is in order. thanks again
 
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