Intermittent no start

GeorgeKohler

GeorgeKohler

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Joined
Feb 3, 2015
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33821
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159
Hi All,

Mercruiser 5.0L carb'd Bravo III. Two seasons ago, I replaced the starter because it was turning very slowly even with two fully charged brand new batteries. After the starter replacement, it turned over perfectly for a year.

Beginning late last season, after spending an hour or so on the hook for lunch, I'd turn on the blower for 4-5 minutes and then turn the key. All the electronics would power up, warning beeper would sound, but then NOTHING when I turned the key to start. I mean nothing. Not even a solenoid click. I opened the engine hatch, checked some battery/starter cables (all were pretty tight and didn't seem corroded), tapped on the starter a few times, turned the key back and forth a few dozen times, still nothing. Then, all of a sudden, it turns over, nice a fast like I've got two fully charged brand new batteries and a brand new starter. This has happened 5 or 6 times on the water now.

I can't seem to make it happen in the driveway. Turns over 100 times out of 100. I think it has to do with the heat building up in the engine compartment, and then cooling off with me tinkering under the hatch. I don't think my wiggling cables or tapping the starter has anything to do with getting it to start.

Could it be a bad key switch? Bad slave solenoid? Bad solenoid on the starter? Corroded/loose cable somewhere?
 
Statistically, it's the Slave Solenoid. When I've seen them go bad, they've clicked, though. So, it could be the key switch or neutral star switch as well. Not the Dead Man Switch. That lets your engine crank but doesn't provide ignition.

I'd say, rig a Test Light, or place a Meter where you can see it, and try cranking in Neutral. If it lights, or responds, then change the Slave.

I really doubt it'll get any deeper than that, but next, the main engine harness connector. That, and engine ground from battery.

Slave Solenoid! Not bad to have a spare.
 
I thought about the neutral start switch after my last episode, but that's in the throttle handle, correct? I never touched that during any of the episodes.
 
Most of the neutral safety switches are not in the handle but below in the "guts" of the FWD/REV cam mechanisms. I'd check the master connector that's connects the various wires to the power plant. Some times they get Mr. Green Jeans on the contacts. Measure the voltage to the Slave starter solenoid when its starting and not starting. Good Luck.
 
I had the wires on the back of the key loosen up. Gave me the same symptoms.
 
Intermittent electrical problems are tough to figure out. I've had two on my port engine. It would shut off like you turned the key. Both times it would turn over though. Once was a bad ignition wire (purple) in the harness and next time it was the pickup coil inside the distributor. With your engine not cranking, first thing I'd check is the ignition switch then the ground to that engine.
 
Intermittent electrical problems are tough to figure out. I've had two on my port engine. It would shut off like you turned the key. Both times it would turn over though. Once was a bad ignition wire (purple) in the harness and next time it was the pickup coil inside the distributor.
 
If you hear a click, it's the solenoid working. All the solenoid is is an electromagnet that pushes or pulls a steel rod that connects two contacts. The solenoid in/on the starter gets it's power from the slave solenoid and it should click, too. This solenoid takes more amps to run as it also pushes the starter gear(bendix gear) out to engage the flywheel. There's also another way the bendix gear engages the flywheel by being pushed out along the starter shaft by way of a helical groove and sleeve in the bendix gear and the centrifical force of the starter. I know, more info than you wanted to know...but if you know how something functions, you can repair, maybe in an emergency.

Back to the other solenoid that pushes a steel rod to make a connection at one end and the other end pulls a couple of levers that pushes the bendix gear out to the flywheel. This system can have a couple causes that pushes the bendix gear short of full engagement and can cause LOUD grinding. At the end of the system of levers that push the bendix gear is a fork that engages the bendix by way of short pins that engage the bendix. The forks are soft metal that bend over time. Just bend them maybe 1/2" out so they'll engage further. This repair can be done if stranded or emergency on the boat. Just disconnect the battery before working on this high amperage component.

Oops! The slave solenoid can indicate the electromagnet working but the electrical contacts will get burned away over time from the sparking during the 'make and break' of the connection.
 
1st just be sure to move the control shift a bit F & R while key is to Start position, in case the N safety-start switch is a little out of adjustment.

You can also test the ign. switch to confirm there is continuity between the B ( battery) terminal and S (solenoid) terminal in Start position.

If there is you can try jumping (car jumper cables you should have onboard) from battery+ or the big battery+ terminal on the starter solenoid to the remote starter solenoid. Then next to the starter solenoid.

Confirm all battery + & neg cable connections are tight with 0 corrosion , including at the engine neg. grounds.
 
No click indicates no juice to solenoids. Neutral switch, key switch or battery connections. gauges going dead when switch is turned points to high load circuit not working while switch is working. battery or connections most likely.
 
If there's a way to energize the Starter Solenoid, you'll here it Click. More like Slam In. It'll be LOUD. The Slave is barely audible unless you are hovering over it or the whole area is completely quiet when you try it.

The Slave failure I had, went like this: It DID click, just didn't make Contact. I had good batteries in the boat. If I had just charged the batteries, meaning their voltage was actually Above Normal, Slave would pull in, click, and energize the actual Starter Solenoid. A few hours after charging, it would again Click, just not energize the Starter.

BE SURE you have "signal" from the Key Switch to the Slave. Then listen for Click. But Click, at least by me, does not always mean Good.

SAFETY WARNING: Be careful of any jumper wires and temporary switches in the Bilge Area!
 
For what it's worth, the solenoid on my son's trim pump (which is the same part number as his starter slave solenoid) would also click, but it wasn't making a good electrical connection inside so the pump wouldn't run.

It's a cheap part to replace (~$25) and at least in my area both NAPA and O'Riley stores carry Sierra Marine parts, so you don't even have to go to the marina to get one. If the starter is new, and the wires/connections are all good, I'd be looking at the slave solenoid too.

Adam
 
Read very little of this post but what little I read sounded like symptoms I had on my '93, 37C. First thing I replaced was ignition switch; cheap but not solution. Swapped starter solenoids; still no solution. Bottom line fuel pressure switch did the trick. Good luck.

BOB J
 
Too much chatter without hearing from the OP.

Yo! George!

What's happening?
 
Haven't had time to try anything yet. Problem is, I can't make it happen in the driveway. I think I'll swap out the slave solenoid this weekend.
 
Thanks for giving us an UP, George. We'll be watching, waiting for good news.

Do you have a Helper, or can you rig a 12V test light hands free at the Slave so you can look back and see if you're getting power to it when you turn the key to START?

There's a "Mechanic's Starter Switch" that connects Hot to Solenoid to crank an engine from under the hood for things like compression tests, valve adjustments
41wJAPb7G2L._AC_US218_.jpg


If your Slave looks something like this
4111Ytd5dzL._AC_US218_.jpg


Then Red and Black on the two larger studs and you push the yellow button, starter should crank as log as the Battery is ON. Key switch can be Bad or Off. Slave can be Good or Bad. Of the small terminals, one should have continuity to GROUND. Connecting Red or Black to the OTHER small slave terminal, and the other to Battery +12 VDC, press Yellow button, Slave should crank Starter even if Key Switch is Bad or Off. This diagram is supposed to be MerC.
2011-11-12_235025_starter_wiring.jpg


EDIT: I would label the one on the Starter as "Primary" and the one triggered by the Key and Neutral Switches as "Slave." The way the diagram is labeled is truth of how it operates, but you talk to a MerC "person" (parts or mechanic) and say "Slave" they'll show you the little one I pictured and we've been talking about!

OH, Slaves used to come two ways. One with a flat bottom that could fasten to a flat surface. Another with a dimple on the bottom that needed a surface with a hole or dimple in it in order to mount. Hopefully that foolishness is over.
 
yes , as J-D suggests , I'd jumper to or across any suspect start circuit parts to isolate a culprit before buying/replacing parts. And if there is a fuse down on the starter solenoid as in the diagram, you might just swap that out and check for corroded holder contacts.

Clean/tighten any corroded/loose contacts at ignition switch, slave/remote solenoid , neutral start switch, starter solenoid, engine ground and batteries.

Next time it happens , I'd suggest you have someone hold the key to Start while you wiggle the heck out wires to each of those components and harness plug to see if it suddenly cranks when you are near a suspect. Just don't keep it on Start very long at a time, though if the starter is not drawing amp juice that may not matter.
 
For $25, I replaced the slave solenoid. It was fairly cheap and quite easy. Bad news, started 10 times out of 10 at the dock at the beginning of the day. After 2 hours of cruising, got back to the dock, shut her down and immediately tried to turn it over. Same problem. Opened the engine hatch and touched nothing for maybe 10 minutes. Turned the key 4 or 5 times and on the 5th turn, it cranked right over, real strongly, and started right up. Turned it off and restarted it 5 times in a row.

So, what part of the starting system doesn't like the heat?
 
Here's an idea.... What if I replaced the current 160* thermostat with a 140* thermostats? It would keep the engine cooler and circumvent the issue altogether.
 
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