Engines just die randomly

[AfterHours]

I'm at my wits end, any ideas or where to start, I have a 99' 330 with twin 5.7l Mercs.

The engines have died twice when shifting to neutral while docking. First one engine then immediately the second. Both times have been after full day on the water, with multiple stops without problem. Took the boat out the day after this happened the last time and didn't have a problem, I'm worried about getting stranded on the  water.

Coincidently or not, I had a wiring problem to the blower, and wired the blower into the transom light wiring. 

Talked to a marine tech and he thought it was a fuel problem, but engines run of seperate fuel tanks, and not crossfeed. 

Any help or ideas would be greatly appreciated!

[Greg]

Mercs or Volvos?

Greg

[AfterHours]

Greg, Mercs.

[Greg]

I'm no mechanic, and this is may be a shot in the dark....but, a guy in my marina just dealt with a similar issue.  Here is the background, he has a SeaRay with Mercs and was having an issue with engines simply dying, and also (and more frequently) the engines randomly not going into gear.  Initial thought was that he may have both an electrical problem and a transmission issue.  Turns out both problems were traced to the batteries.  He changed his batteries and both problems went away.   Related to how the alternator works on a boat.

Best I got.........

Greg

[dazeoff]

I agree with Greg on the Battery deal , but also the shifter on the helm and the lock outs on the motor could be worn and acting up ..it does sound electrical to me ....because it happens only when docking ... If it is an immediate shutdown it is electrical  , fuel would act up a little first ...just my 2cents worth ...

[Babyboomer]

I agree with Greg on the Battery deal , but also the shifter on the helm and the lock outs on the motor could be worn and acting up ..it does sound electrical to me ....because it happens only when docking ... If it is an immediate shutdown it is electrical  , fuel would act up a little first ...just my 2cents worth ...

but also the shifter on the helm and the lock outs (both shifters would not go bad at the same time) I also say it's electrical) I know nothing about twins I run a single screw but can you or do you have each engine on a seperate battery say hook up one engine to the house battery in my book if then only one engine stalled then you would prove it to be battery. Just my 2 cents

[frodo13056]

I'm willing to bet that it's the momentary kill switch(s). If you look on the side of each engine where the shift and throttle cables mount to the exhaust manifold, you'll see a small switch (micro switch) with a roller on the end of it that fits into a detent on the shift plate - this is a momentary kill switch that is used when shifting between neutral and reverse. The shifting mechanism in a Mercruiser lower unit involves a drive gear (forward) and a reverse gear and when shifting, that gear needs to be able to release from it’s drive gear.
The reason this switch is there is to eliminate a phenomena known as "gear bind". Gear bind occurs due to the shape of the gears where you have a "drive" side of the gear and a "coast" side of the gear. The drive side of the gears are at an almost 90 degree angle to each other, thus ensuring that you have maximum gear face to gear face contact (spreading the force over a greater area reduces the force on any single point). The Coast side of the gears are more at an angle and have less gear to gear contact. Anyway, since there is no "coast" in a lower unit - the drive gears are always "driving" (maximum gear to gear contact) - which results in gear bind. To release the gear bind, Mercury uses a momentary kill switch when shifting into reverse - without the momentary kill switch, it's darn near impossible to shift into reverse due to gear bind.
It’s kind of complex how those momentary switches work but here’s another explanation:

http://sterndrivetools.com/Replace%20your%20R,%20MR%20or%20Alpha%20One%20Shift%20Cable.html

I’ve had to fiddle around with these things and it’s a real pain in the @$$. Best way to check this is to connect up a portable tach (or a test light) and watch what happens when you shift – and, yes, if the shift plate or momentary kill switch is off even a little, it will kill the engine even when shifting from forward to neutral. Why is it happening to BOTH engines? My guess is that both shifters are used the same amount and are wearing at the same rate.

That’s my guess as to where to start – but I could be wrong 

Hope this helps!

Steve

[dazeoff]

Great information Steve , I had that problem on My Thundercraft 5,7 ...That article explains it well , His boat being a 99 , could well be the problem , it is a great starting point ....John

[Babyboomer]

What drives Alpha or Bravo?

[Capt Ron]

I'm willing to bet that it's the momentary kill switch(s). If you look on the side of each engine where the shift and throttle cables mount to the exhaust manifold, you'll see a small switch (micro switch) with a roller on the end of it that fits into a detent on the shift plate - this is a momentary kill switch that is used when shifting between neutral and reverse. The shifting mechanism in a Mercruiser lower unit involves a drive gear (forward) and a reverse gear and when shifting, that gear needs to be able to release from it’s drive gear.
The reason this switch is there is to eliminate a phenomena known as "gear bind". Gear bind occurs due to the shape of the gears where you have a "drive" side of the gear and a "coast" side of the gear. The drive side of the gears are at an almost 90 degree angle to each other, thus ensuring that you have maximum gear face to gear face contact (spreading the force over a greater area reduces the force on any single point). The Coast side of the gears are more at an angle and have less gear to gear contact. Anyway, since there is no "coast" in a lower unit - the drive gears are always "driving" (maximum gear to gear contact) - which results in gear bind. To release the gear bind, Mercury uses a momentary kill switch when shifting into reverse - without the momentary kill switch, it's darn near impossible to shift into reverse due to gear bind.
It’s kind of complex how those momentary switches work but here’s another explanation:

http://sterndrivetools.com/Replace%20your%20R,%20MR%20or%20Alpha%20One%20Shift%20Cable.html

I’ve had to fiddle around with these things and it’s a real pain in the @$$. Best way to check this is to connect up a portable tach (or a test light) and watch what happens when you shift – and, yes, if the shift plate or momentary kill switch is off even a little, it will kill the engine even when shifting from forward to neutral. Why is it happening to BOTH engines? My guess is that both shifters are used the same amount and are wearing at the same rate.

That’s my guess as to where to start – but I could be wrong 

Hope this helps!

Steve

I will echo Steve's explanation. Your shift cables will stretch with time and the micro switches are doing what they are suppose to do, kill the engines momentarily while you shift gears.

[dazeoff]

If you go this site and scroll to the bottom you will see the two Shift cut out senders , and what they look like . if you have a repair manual , it will take you thro the steps to test it .. seems easy , however i agree with the thread , it probably has something to do with streached cables or adjustment of the switch ...     
          http://www.mercstuff.com/shiftplatekits.htm

[Greg]

Capt. Ron....

would the engines actually "die" as AfterHours mentions, or would they simply delay?

Greg

[frodo13056]

The momentary kill switch grounds the coil - so it actually causes the engine to stop running (no spark) but it's tough to notice unless you have decent tachometer and are watching the tach when you shift to reverse. If you do watch the tach, you'll see the RPM's drop to almost nothing - but since it happens pretty quickly it's hard to notice. If you simply listen to the engine, you might not notice it at all - because momentum keeps the engine spinning without spark. Keep in mind that when properly set, the momentary kill happens within a second or two, releasing the gear bind and allowing the neutral to revers shift. Without the momentary shut down of the engine (loss of torque), you would not be able to release the gear bind - thus making shifting to reverse very tough.
If the kill switch is engaging when shifting from forward to neutral due to miss-alignment (worn cables or worn components), it'll be pretty obvious - you can check this by having someone shift from forward to neutral, neutral to reverse while you have eyes on the shifter plate.
By the way, there is a special grease that you are supposed to use to grease all shifter cable pivot points - an often overlooked preventative maintenance step.

[Capt Ron]

Capt. Ron....

would the engines actually "die" as AfterHours mentions, or would they simply delay?

Greg

Yep, it will kill the engines entirely. This is because the cables leave the micro switches in the off position instead of the quick switch mentioned in frodo's explanation.

[Babyboomer]

If you go this site and scroll to the bottom you will see the two Shift cut out senders , and what they look like . if you have a repair manual , it will take you thro the steps to test it .. seems easy , however i agree with the thread , it probably has something to do with streached cables or adjustment of the switch ...     
          http://www.mercstuff.com/shiftplatekits.htm

I'm putting that link in the Library it's in the Mercruiser Column