PLEASE HELP!! Mercruiser DIES!!

[goneboating06]

Please i have tried everything i know and i need help. My engine will just die randomly at any rpm range, it has great fuel pressure, and the gas is new but it will just die and start right back up again afterwords as if nothing was wrong then just die AGAIN!! My boat a 1998 milan with a mercruiser 5.7L v8 with thunderbolt ignition. It is carbed with a 4 barrel weber but not fuel injected and it has a mechanical fuel pump. I have replaced the rotor, distributor cap, coil, spark plugs, and spark plug wires hoping that it would help but it didn't. I replaced the water seperating fuel filter but that didn't change a thing. The timing is right on and it doesn't suputter or anything it just dies like ignition was cut. I have checked voltage going to the coil and it has good voltage when it dies, its just a mystery to me. Please help!

 

[Bondo]

Re: PLEASE HELP!! Mercruiser DIES!!

Ayuh,.... Welcome Aboard,...

This is the Factory Service Manual for your motor,....

It covers diagnostics pretty good.....

 

[bhammer]

Re: PLEASE HELP!! Mercruiser DIES!!

Follow the troublshooting guide that Bond-O supplied but it sounds like you have an electrical problem. Maybe a loose connection or a bad ground?? What happens if you just run it on the muffs?

 

[flabum]

Re: PLEASE HELP!! Mercruiser DIES!!

I agree.....sounds like an electrical problem. Check all the connections at the motor, battery cable at both ends, wires at the key switch and kill switch, check for arcing at the coil and check the cannon plug. The cannon plug pins can collapse during use. If you look at the pins, you will see they are split down the middle. Using a sharp knife, slightly spread them.... the gap should be about .060......any further and they can break. By spreading the pins, the contact will be tighter there.

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

Thanks for replying so fast. It does the same thing on the muffs. For the past 3 months thats all we have been able to run it on but it seems to get worse everytime we run the engine. There are 2 black wires with a circle type connector that look like ground wires that dont connect to anything. one is twards the front of the motor by the thermostat, and the other is by the distributor, they are not bolted to anything they just hang around. Could this be anything to be worried about. I tried touching them to the block while the engine was running but nothing happened. But i will check that cannon plug. Thanks again you guys for your help i will keep posted on whats going on.

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

I checked the cannon plug and got a spark plug gap tool and set the connectors at .060. I started it up and it is still doing the same thing. Any other suggestions? I also checked and double checked connections everywhere and they look fine... am i missing something? thanks again!

 

[Limited-Time]

Re: PLEASE HELP!! Mercruiser DIES!!

This may be a tough one to sort out. Intermittent problems are generally the hardest to pin down. Is the problem constant, or random?? I chased down a similar problem last year. Boat ran great till it died, then it would restart and run fine. I tracked the problem to the ing. (purple) wire shorting out to a bracket holding the radio in place. When the boat was manufactured the excess wire in the wiring harness was wrapped around the afore mentioned bracket. The bracket cut through the wiring harness and into the ing. wire but only enough to intermittently short out. To top it off, because the wiring harness was wrapped around the bracket several times the cut was well hidden from view. It took several attempts of several hours each to chase down the fault.

 

[cyril420]

Re: PLEASE HELP!! Mercruiser DIES!!

The most likely culprit is the ignition sensor located in the distributor. The piece the white/green and white/red wires come from. It is easily replaced (just two screws. These cause all types of ignition problems

 

[bhammer]

Re: PLEASE HELP!! Mercruiser DIES!!

Do you have an ignition / plug tester. You could hook that up and see if ignition is still happening when the engine dies. Does this year motor have the ability to download codes?

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

I don't believe its able to download codes, but it dies totally random, and now its getting worse. I am completly stumped. I was wondering about the ignition sensor.... Does this problem sound like a fuel or ignition related problem... I MISS MY BOAT!!! thanks again!

 

[RJLeuwen]

Re: PLEASE HELP!! Mercruiser DIES!!

I checked the cannon plug and got a spark plug gap tool and set the connectors at .060. I started it up and it is still doing the same thing. Any other suggestions? I also checked and double checked connections everywhere and they look fine... am i missing something? thanks again!

You need to eliminate the boat from the engine. Disconnect the so called cannon plug from the engine, jumper wire from battery+ to + side of coil, jump from bat + to yellow/red stripe wire on starter solinoid (BEST USE A REMOTE START SWITCH no sparks in bilge area)!! see if problem still occurs, disconnet coil jumper to turn of engine.

RJ

 

[bhammer]

Re: PLEASE HELP!! Mercruiser DIES!!

Use the troublshooting link that was posted. It will help you determine what your problem is or narrow down your search. It is too hard to tell what the problem is and I wouldn't throw parts at it trying to fix it.

Try running it and move/wiggle all the wires around to see if you reproduce the issue. This includes wires at the engine and the helm.

 

[Maclin]

Re: PLEASE HELP!! Mercruiser DIES!!

If you have good voltage at the positive side of the coil when it dies then it is the sensing circuitry on the other side of the coil. The negative side of the coil is grounded and ungrounded to produce spark, the ignition control unit figures out when to do this based on a signal it receives from the sensor inside the distributor. Could be that sensor, could be the wiring between the two. It could be something else connected to the negative terminal causing the interference. What else is hooked to the negative terminal? I do not know the Thunderbolt ignitions that well to know if the tachometer sensing wire hooks to the coil at the negative terminal or hooks to the control unit. If there is a tach wire on the negative coil terminal, they are usually gray I think (and they will not be the only wire) then remove it and see it it behaves differently. Tachometers can go bad and short out inside. When this happens it effectively removes any signalling the control unit is providing as the coil will be grounded thru the bad tach all the time.

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

Well.. there are two wires on the negitive side of the coil do i remove both of them then just ground the negitve side of the coil seperatly or do i just remove one wire or find out what wire goes where? Thanks?

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

I tried the tachometer thing and it behaved just the same as before. I have wiggled wires everywhere and i cant seem to find the problem... this boat only has 175 hours on it.. it sat for quite a while before we got it. Thanks for the help

 

[RJLeuwen]

Re: PLEASE HELP!! Mercruiser DIES!!

Try post #11

RJ

 

[packerman]

Re: PLEASE HELP!! Mercruiser DIES!!

As I'm reading these post...... and I know this is a help forum, I can't help but wonder if this is one of those that are better taken into the repair shop. They may have seen something similar to this through the sheer volume of boats they work on. I'm sure you've learned alot about your boat through this and it may come in handy in the future but if you manage to solve this problem, you probably w/never see it again in your life. Unlike changing seals in the lower unit, etc. which learned, will be useful many times over. I'm sure your thinking "I've tried almost everything, I must be close". Maybe, maybe not. I'm just sharing a thought. Post #11 as mentioned prior, sounds like a good place to go if you continue on........... sounds like that might eliminate half for you. Good luck!!!!

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

Yeah your right.... it would be tons better to go and take it to a shop to be worked on, and i would have 4 months ago but the problem is i live 300+ miles away from a boat mechanic so all i can do is take it to an automotive mechanic and i have. So i turned to the people that know these boats inside and out here at iboats.com hoping that somebody would know what to do. Thanks though... Anyways i disconneced the boat from the engine like on post #11 and did what he suggested and it is doing the same thing... Could it be the ignition sensor? i am confused...

 

[bhammer]

Re: PLEASE HELP!! Mercruiser DIES!!

Go to this link: http://www-alt.mercurymarine.com/mnetdata/SERVICE/CRUISER/Servmanl/24/24covr1.pdf Go to section 4B. Under each major component, there are proper tests to perform that should find your broken / intermittent issue. This is where you need to continue from.

 

[goneboating06]

Re: PLEASE HELP!! Mercruiser DIES!!

Ok... i will try it and keep posted on whats going on. Is it possible it could be a carb problem...