Starting/Running issue- Only runs when holding key in start

[eriki]

1994 Mercruiser 4.3LX Thunderbolt IV- Alpha one gen 2

Ok this is my first post on here, been looking around for a while now and have a little issue hopefully I can get some help with.

Over the weekend I did all my bellows, impeller and shift cable and also cap and rotor. Here's a little information of what's going on/what happened. When I went to start the boat after the bellow change and everything the battery was dead, jumped the battery motor stated right up (on Muffs) it ran for about 40 seconds then died. Started it back up it was running fine went to give it some gas and it died. I go to start it up again and as soon as I let off the key it died, try it again same thing. But if I start it and hold the key all the way in the starting position it will run but die as soon as I let off the key or it will die when I'm holding the key in start and I give it gas. Prior to doing all of the bellows and everything the motor ran fine and even had it out on the water 2 weeks ago when I found out the shift bellow was ripped, over the past month I have done a new fuel filter, spark plugs, oil and filter, new fuel vent, it has brand new gas in it. I Have no idea why it just started doing this and would really like some help to try and get it running.

From looking around last night on here I have thought maybe it could be the ignition switch, or a ballast (if I have one?), possibly a fuel issue?. Any ideas on what I can look for? Also if there is any other information/history needed please let me know.

Thank you

 

[Fishermark]

Almost sounds like your oil pressure switch or connection is bad. Do you have an electric or a mechanical fuel pump?

 

[eriki]

If the oil pressure switch was bad wouldn't it not start at all though? the oil gauge is reading 40psi when it runs and when it did run before it was reading fine. For the fuel pump I think its electric but I'm not sure I cant remember. I only looked once I also have only owned the boat for a little over a month now.

Another thing I am thinking is that my dad was messing with the interior siding and was going to pull it off to put new upholstery on it and he didn't know that the controller was hooked up with a bunch of wires behind it, I'm thinking he may have possibly pulled a wire or wiggled one loose from the lanyard kill switch? or possibly something else, but then I don't think it would have started and ran those first 2 tries before it stopped wanting to run without the key in the start/cranking position.

 

[Fishermark]

When you turn the key to the start position the ignition receives the voltage through the starter. After you release the key the power goes through the oil pressure switch. If the switch "says" that there is no oil pressure it will kill the ignition. A bad switch or connection with give a false reading. That at least would be a good place to start looking.

On the wiring problems your dad may have caused... the kill switch if disconnected will usually not even allow the starter to engage. It will do nothing.

 

[eriki]

Ok, I will have to look at the switch later today. Other than that what else could cause this problem? It just seems odd that it ran fine a week ago and then now it wont and also the fact that if I tried to give it gas it dies,

I have read the stickies on starting issues but haven't had the chance to test anything out yet as I am at work.

 

[bobkat1864]

Hi there...with the key in the "run" position, do you have voltage at the "I" terminal of the ignition switch?

 

[eriki]

I have not yet had a chance to check, I am at work currently.

 

[stonyloam]

It does sound like the oil pressure switch. The fact that it started and ran for a time after the switch went back to run indicates that it is probably not the ignition. The fuel pump would have run when the starter was turning and the engine would have run for a while on the gas in the carb. If there is no oil pressure or you have a bad switch it kills the PUMP, so you do not pump the bilge full of gas if you have a fuel line rupture and the engine dies. It should have a fuel pump relay that is activated by a wire coming from the oil pressure switch. You could try jumpering 12v to that wire to see if it will run. Good luck.

 

[eriki]

Yea I am going to try jumping the wire later when I get home and see if will work. so basically I just put a jumper wire on the 2 terminals on the oil switch and listen for the fuel pump to run? or do I try and start it to see if it runs that way?
Another thing I'm going to check is the shift interrupt switch since I put the new cable in maybe its tripped the switch? just a thought on that.

 

[Fishermark]

...Another thing I'm going to check is the shift interrupt switch since I put the new cable in maybe its tripped the switch? just a thought on that.

It wouldn't try to start or run when the key is in the start position if the shift interrrupt was engaged. It would crank, but no try to start. From everything you describe, I still go with the oil pressure switch or connection.

 

[eriki]

Ok so I just put a jumper wire on the oil switch still doing the same thing. Only runs when holding be key. So now what

 

[Fishermark]

With the key in the "run" position, see if you have 12v at the positive post on the coil.

 

[eriki]

Well now when I go to turn the key j get nothing at all not even clicking, it doesn't do anything and also I was showing 0 volts at the coil

 

[eriki]

Also I have voltage to the ignition switch from the battery and the start positions

 

[eriki]

I did not get to check the slave solenoid as I was by myself so I couldn't have someone put it to the start position. I'm honesty at a loss of what it could be. I really want to get it running. Can anyone chime in on this?

 

[Fishermark]

If you have no voltage at the positive side of the coil with the key on in the run position, then you have a wiring issue somewhere. Check the big cannon plug where the engine harness plugs into the boat wiring harness. You will just have to start working backwards and checking all the connections, etc. You say you have power to the switch. Do you have 12v at the "ign" side of the switch with the key on?

 

[eriki]

Yes I have power at the B terminal it off position and the S terminal when start position.

 

[Bondo]

I have power at the B terminal it off position and the S terminal when start position.

Ayuh,.... Welcome Aboard,..... That's Good, but ya need 12v at the Ignition terminal, when the key is in the "On" position,....

Should be the purple wire,...

 

[eriki]

I can't remember if I did or not, I am away from the boat now. But if no power at the I terminal would that be causing it to do nothing on the ignition switch? Well let's say I had power and the switch was cranking and turning the motor over, where does this come into play with it dying as soon as I let off the key?

 

[Bt Doctur]

you dont understand, while cranking(start position)power is supplied by the starters solenoid , when you release the key to (run position) power is supplied by the I terminal.