omc v8 starting problem please help

naphobia

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ok, i'll try my best to explain. i have a v8 305 gmc. while boating a pluf off cap busted resulting in the bildge filling with water. so i ordered it an installed.(simple) now on a different note i was having ignition problems found out i had a short at the fuse box. the problem was that the ignition wasnt working right the dash lights would come on sometimes, when they did the ignition would work when they didnt the ignition wouldnt. so now the problem is some what fixed. the ignition is working great but the dash and gadge's dont work..all that said the problem i need help with( hoping that some of the above might be useful to determine a soloution). the engine is turning over, its fireing then dies. seems fuel related but i can see that gas is getting to carb. i try starting it with the throttle all about midway. (no choke on key) and its like it fires up but dies immeadiatly. so my only thought are something got wet.but like i said it fire's just wont stay running. i am sorry if im not explaining that well but anyone who has so time to trouble shoot this with me i can answer any questins. i have gone through it like it was a v8 car an havent gotten anywhere with. so thanks in advanced not dure if im allowed to post my email or not but if we could email each other back an forth that would be great
 

Don S

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Re: omc v8 starting problem please help

First off, Welcome to iboats.
Second, what year is this OMC? What drive?
 

naphobia

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Re: omc v8 starting problem please help

thank you, its a 87 omc cobra, 5.0 305 , on the engine it has model number 504APARY serial is t0959019 on the drive it has model# 984542 and serial#t0496255 i hope this helps.....also let me just add, the boat ran great before... and also i had it running once after the the plug off cap issue....not it starts it just doesnt idle it just dies thanks again
 

Don S

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Re: omc v8 starting problem please help

Do you have power to the plus side of the coil with the ignition switch in the run position (engine not running)? Are you in salt water? If so, how long since the boat got wet like that, and the problem showed up?
 

naphobia

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Re: omc v8 starting problem please help

id have to check if i have power to plus side of coil but it was a week or so since it got wet. to explain a lil better it as if you started your car an as soon as it started to turned off the key
 

Don S

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Re: omc v8 starting problem please help

I know exactly what you are saying, that is why I ask. Go check, sounds like a resistor wire may be off/missing/corroded etc.
Salt water (Y-N)
 

naphobia

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Re: omc v8 starting problem please help

i will check in the morning and post out come. the the wire your talking about a fusable link because one other thing i did was i open a fuseable link (wire to check fuse) and touch wire to motoe resulting in it poping. one the the really small glass fuse's i replaced it but im not sure excatly what fuse number is. so i replace with one that looked like the same size strip of metal in the midle. the wire is located right behine the carb and is red... again i cant thank you enough for your time
 

Don S

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Re: omc v8 starting problem please help

Here is a link to the Wiring diagram for your engine.
The purple/black wire from the starter to the the coil IS working, that is why it runs when you have the starter engaged.
With the key in the run position, the power to the coil need to come from the purple/red (PU/R) wire from the alternator to the coil.
 

naphobia

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Re: omc v8 starting problem please help

i love this forum thank you very much for your help i will study it tonight an try my best tomorrow and get back in touch
 

naphobia

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Re: omc v8 starting problem please help

looking at the diagram in the middle there is a r/pu that is the fuse is he fuse i busted ...(that is off the subject) but i was just curious what that is for? i will still have to check the coil...just wanting to get familar with it...thanks again
 

Don S

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Re: omc v8 starting problem please help

Follow the wires to the unit it operates. That is what it goes to.
Assuming you are talking about that 20A fuse, it goes to the controls for the trim & tilt controls.
 

naphobia

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Re: omc v8 starting problem please help

ok i couldnt wait....ok the purple wire comeing from alternator to coil with key i have no juice. so we are clear the color i guess are wrong or im an idiot...the alternator has an orange fat wire and a purple wire. at any rate, i turned the key on put the tester on every not/ wire on coil an didnt have any juice. sorry for my ignorance
 

Don S

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Re: omc v8 starting problem please help

Go directly to the ignition switch. With it in the RUN position, the purple wire should show battery voltage, does it? Are all the wires good and tight on the switch?
 

naphobia

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Re: omc v8 starting problem please help

yes about 15, and yes the wires are all tight. actually before i realized im have a short in the fuse box i bought a new ignition switch...
 

Don S

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Re: omc v8 starting problem please help

How do you get 15V (or even almost 15V) without the engine running.
You aren't using the dash volt meter are you?
 

naphobia

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Re: omc v8 starting problem please help

when you said in the run position you meant just turn the key on not try to crank and check right? cause the ignition is working i have power to it an with key in on position i have juice to purple wire ...when i crank it up it starts an dies imeaditly.....i believe we are on the same page an you know what I'm saying....i just wanted to clarify
 

Don S

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Re: omc v8 starting problem please help

BTW, you are not having a "Short", your are having an open.
I suppose you aren't familure withg using a DVM (Digital Volt Meter)?
 

Don S

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Re: omc v8 starting problem please help

when you said in the run position you meant just turn the key on not try to crank and check right?
Yes, just the on position. That is where the key will end up if you go to start and the engine starts and keeps running when you let off the key.
 

naphobia

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Re: omc v8 starting problem please help

no im not but i think i got it this time 11.86 sorry im useing a multimeeter, set on dcv at 20 .
also i checked the red just for the heck of it ands its the same...but i guess it should be since thats coming straight from battery
 

Don S

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Re: omc v8 starting problem please help

Do you have a kill switch? The one where you put the safety lanyard. If so, do you have power to it and after it, then keep going all the way back to the engine. Both sides of the plug and follow the power.
When you do have to puncture a wire to test for power. After testing, immediatly cover it with Liquid electrical Tape. Like this:

84104-LET.jpg
 
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