4.3 mercrusier starts, then immediately dies!!!

[ljenks]

Ok guys, I am an ATV mechanic that can't seem to find out what is going on here. Basically, last year the boat (2007 Tahoe 215 w/ 4.3 mercruiser carbureted) ran fine all last year. Winterized the boat. Just went to start for the first time last week & it would start for only a second or two, no more, then immediately shut off. I tried choking, giving it gas & everything & still would only run for 1-2 secs, then shut off.

Finally got it to my shop today & tried diagnosing, but not familiar with it at all (not an ATV)!!!! I started looking at this forum some & found there was alot of talk about maybe an oil pressure switch being bad??? All I have done is disconnected the fuel line at the carb & applied 12vdc directly to the fuel pump to make sure it is working & it did. I have also remove the fuel/water seperator filter & found no water or sediment in it at all. Went ahead & replaced it while I was there.

My oil pressure switch is located at the back of the motor on top. It has only one wire going to it (can't remember the color). Someone told me to disconnect it & jumper it to ground. I tried that & still nothing???

Any ideas & tips would be greatly appreciated!!! Maybe some of you guys have ATV's that I could return the favor with.

Thanks so much
Larry

 

[Bt Doctur]

Re: 4.3 mercrusier starts, then immediately dies!!!

That sounds like the oil sender for the gauge, the oil pressure switch is normally down by the oil filter area and has a 2 wire plug.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

Ok... Maybe I was looking at something different. What I saw was some type of pressure switch located on the top of the motor, near the distributor sticking straight up with only one wire on it?

How exactly do I go about testing or bypassing this switch to see if it is bad?

Also I did disconnect the 2 wire plug at the fuel pump & used jumper wires to apply 12 volts to the pump at all times & it still would not stay running? Maybe because I had the harness unplugged & the other end of it caused an open circuit?

Thanks so much for the help

 

[Bt Doctur]

Re: 4.3 mercrusier starts, then immediately dies!!!

The mercruiser manual is available in the Adults Only section.It will have the wiring diagrams.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

I have briefly looked there & could not find the manual for my year? Mine is a 2007 carbed 4.3. Any ideas??

Thanks again.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

I am new to this forum & see where a lot of people have viewed this thread, but not a lot of responses, hints or help??

From searching through the forum, this seems to be a fairly common problem.

Any help from anyone??????

Thanks again.

 

[tractoman]

Re: 4.3 mercrusier starts, then immediately dies!!!

Does it have an engine kill switch and is it switched to off? I just woke my boat up this weekend, and forgot to switch it to on. It had me scratching my head for a few minutes, then when i switced it to on, she fired right up. It's worth a look.

 

[TahoeQ4Pilot]

Re: 4.3 mercrusier starts, then immediately dies!!!

Does it have an engine kill switch and is it switched to off? I just woke my boat up this weekend, and forgot to switch it to on. It had me scratching my head for a few minutes, then when i switced it to on, she fired right up. It's worth a look.

x2, happened to me after launch last year. I couldnt get it started, recovered to the top of the ramp to troubleshoot. Come to find out the deadman switch was tripped.

 

[boat127]

Re: 4.3 mercrusier starts, then immediately dies!!!

i would start by reading the manual and check the kill switch as posted above.
sounds to me like the kill switch is off if it is to the on position then i woulld switch it to off then back to on a couple times jsut maybe a bad connection in there. hope this helps

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

Thanks so much guys, I will check that out tomorrow. I assume you are talking about the switch that is located on the bottom of the control/remote?

Thanks again... I will post what I find out tomorrow.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

x2, happened to me after launch last year. I couldnt get it started, recovered to the top of the ramp to troubleshoot. Come to find out the deadman switch was tripped.

What do you mean it was tripped?????

Is there a way for this switch to actually trip? Or does someone have to switch it manually.

 

[tractoman]

Re: 4.3 mercrusier starts, then immediately dies!!!

There may be a lanyard connected to the switch to attach to the operator, or it may be just a toggle type switch and yes it should be on the control somewhere. It is manually operated only. I think he meant switched off, not tripped like a breaker trips.

 

[EAVES]

Re: 4.3 mercrusier starts, then immediately dies!!!

Sounds like a bad Ignition switch .....

Shift interupt switch will do this also..

 

[grahamh]

Re: 4.3 mercrusier starts, then immediately dies!!!

If your ignition system uses a ballast resistor, the resistor could have failed--when this happens you'll get spark and the motor will start with the key in the "crank" position, but as soon as you turn it back to "run" the motor will die within a few seconds.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

Can you tell me where this resistor is?

Since I have last posted I have jumpered the wires on the oil pressure switch & it changed nothing. I have also replaced all spark plugs with no help there. I am convinced that it is a carb issue so I pulled top off of carb & removed a few jets, but found nothing clogged? I am an atv mechanic & on atv carbs, there are pilot jets that meter the fuel at idle. Do the mercruiser carbs have the same thing?

 

[Bt Doctur]

Re: 4.3 mercrusier starts, then immediately dies!!!

Try using a jumper from the batt+ to the + side of the coil. This should eliminate a lot of guesswork.If it now runs, trouble is between the ign. switch and the coil.Electronic systems dont use a ballast resistor, only points ign systems

 

[Silvertip]

Re: 4.3 mercrusier starts, then immediately dies!!!

The engine dies because it lost fuel or it lost spark. There may be a resistance wire in the ignition system that is bypassed when the key is turned to START. when you let go of the key the resistor is back into the system again to cut down the voltage. Verify this system is working. An open resistor or an open in that circuit would cause the engine to die the moment you let go of the key.

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

Thanks.... Can I eliminate all of that beings I can get it running sometimes by feathering the hell out of the gas???

 

[ljenks]

Re: 4.3 mercrusier starts, then immediately dies!!!

The engine dies because it lost fuel or it lost spark. There may be a resistance wire in the ignition system that is bypassed when the key is turned to START. when you let go of the key the resistor is back into the system again to cut down the voltage. Verify this system is working. An open resistor or an open in that circuit would cause the engine to die the moment you let go of the key.

I have had it running a couple of times after the key has returned to the run position, so can't I eliminate that issue?

thanks again