97 Mercruiser 3.0LX will run/won't run

[manebeam]

Alright, so I'm not sure where to begin. I've taken my boat in several times now over the last couple of seasons to complain about an issue I am having with my Searay 97 Merc 3.0LX and they keep telling me everything is fine and they can't find anything wrong with it and I keep paying shop time for the nothing wrong with your boat buddy answer.

What happens is, in my yard for the most part I can start and get it running with muffs on, however, sometimes it just cranks over and over but won't fire. When I back it in to the water on the trailer it seems to not want to turn over and just cranks and won't fire. When it does start and I dump it in the water and get going it seems to run perfect and I'm like wow it's like brand new and awesome and it will run for an hour beautiful then all of the sudden it shuts down and I can't get it running again. Other times it runs for a short time and stops and I can't get it going again. It's like it's flooded but it's not. It has stranded me numerous times and I am scared of it now. I have told the shop this and they tell me everything is fine as they can't find anything wrong with it. Distributor, timing, fuel is all fine they say.

I've just put on a brand new Seastar controller as the old one failed as the guts blew out but I am again hopeful that maybe the old one had something to do with it? On the old one before it failed I replaced the kill switch thinking it was that but nope. I've had the carb rebuilt last year, the best new plugs money can buy last year, new fuel pump, new coil, new key ignition I don't know what else to do. It feels electrical where whatever it is when it works it works and then it decides not to - intermittent in nature. I'm sure it's something stupidly easy. The boat is old but it literally has low hours and is a great looking boat. You'd never know it's 26 years old. Always stored in side so it's not a corrosion issue.

I don't know what else to do besides sink it lol. Any ideas please I'd be so grateful.

 

[dubs283]

You need to find out if you're losing spark or fuel upon shutdown/no start

Pretty simple check, spark tester for ignition. Verification of fuel present at/in the carb. With the choke open you should see two steady streams of fuel when the throttle is advanced quickly

 

[manebeam]

Ok yes I can certainly do that the next time it happens but should either one or both be the case what else could be the problem if I've replaced the old fuel pump, ignition coil, plugs, rebuilt carb, and a host of other electrical things as mentioned in my previous post. I changed all these things in the hopes of solving my problem and I'm still chasing gremlins. PS thanks for replying.

 

[Scott Danforth]

Just throwing parts at it and not trouble shooting is taking $100 bills and setting them on fire.

Start with the basics.
Compression numbers, fuel pressure, timing

 

[manebeam]

Just throwing parts at it and not trouble shooting is taking $100 bills and setting them on fire.

Start with the basics.
Compression numbers, fuel pressure, timing

I so agree with you on that but I only have one place to take my boat to and they've told me that compression, fuel pressure, and timing is all fine. I'm not a merc tech nor a boat mechanic so my skill set is rather limited. I research and I try things within my ability but when I'm told these things are fine I don't have much of a choice other than to believe it. It's easy enough to check for spark and fuel when it happens but the only other option I have is to get them to run it on the lake and pay them big dollars for doing that because they only have tanks and are not on the lake.

 

[dubs283]

It's not acting up for the shop but they did confirm some important things for you

Go boating with a spark tester and a helper, hope it acts up and report back your findings

 

[nola mike]

Ok yes I can certainly do that the next time it happens but should either one or both be the case what else could be the problem

If you're losing spark intermittently then there's a good chance you've got some faulty wiring in the ignition system somewhere. Loose connection, chafed wire, intermittent short to ground, etc. You'll have to confirm loss of spark first

 

[manebeam]

Awesome, I certainly appreciate the feed back. Once the temp comes above freezing consistently I will run muffs first and drop her in the lake once the ice comes off. I will do spark test with my tool when it quits on me. and go from there.

I spent the morning tracing wires and inspecting from the ignition at the helm all the way back to the engine. I've inspected every wire I could get at and I don't see anything suspicious. Grounds are tight, everything is clean. However, I was looking at the shift cut out switch and although it doesn't look to bad overall the connections on the box seem a little loose.

Can this switch go bad?
Am I able to do some kind test on it while I have it off to see if it's gone wonky?

 

[Scott06]

Awesome, I certainly appreciate the feed back. Once the temp comes above freezing consistently I will run muffs first and drop her in the lake once the ice comes off. I will do spark test with my tool when it quits on me. and go from there.

I spent the morning tracing wires and inspecting from the ignition at the helm all the way back to the engine. I've inspected every wire I could get at and I don't see anything suspicious. Grounds are tight, everything is clean. However, I was looking at the shift cut out switch and although it doesn't look to bad overall the connections on the box seem a little loose.

Can this switch go bad?
Am I able to do some kind test on it while I have it off to see if it's gone wonky?

You can measure ohms across the switch to see if it closes when actuated

How did u zero in on shift interrupt ?

If you installed a controller is it tripping the interrupt switch? On water would disconnect it if engine dies and see if it starts as this will kill ignition

 

[Bondo]

Am I able to do some kind test on it while I have it off to see if it's gone wonky?

Ayuh,...... With a multimeter, it's an open circuit at rest, 'n closed circuit when the lever is depressed,.....

They usually don't go bad, til some unknowing sole messes with 'em,.....
'n usually when the motor dies when shifting, 'n it's always the lower shift cable most of the times,....

 

[Scott Danforth]

It's a $6 switch if it is bad

 

[manebeam]

It's a $6 switch if it is bad

Where can I find one such as that? I've looked and they are discontinued. I've found some switches on amazon but they are the wrong size.

 

[Scott Danforth]

It's a micro limit switch. Many manufactured by Cherry it Honeywell. I order thru digikey or Newark.

 

[manebeam]

You can measure ohms across the switch to see if it closes when actuated

How did u zero in on shift interrupt ?

If you installed a controller is it tripping the interrupt switch? On water would disconnect it if engine dies and see if it starts as this will kill ignition

Well after following wires all morning I didn't find anything suspicious. I ended up at the shift interrupt and I got thinking. So I did some internet research and discovered that this switch if faulty, will cause the problems I have. I found out for the most part that over time the plunger will not completely reset causing an interruption and a tow back to shore. I then contacted a relative and asked if he knew anything about these types of switches as he's an oilfield mechanic and he said he deals with them quite often. He said that it is typical of these switches to build up gunk on the inside over time and when they get hot they gum the plunger up preventing it from returning to full position which could cause the problem I am having. He said the same thing that they don't fail but they do gum up. He suggested soaking it in contact cleaner.

 

[manebeam]

Ayuh,...... With a multimeter, it's an open circuit at rest, 'n closed circuit when the lever is depressed,.....

They usually don't go bad, til some unknowing sole messes with 'em,.....
'n usually when the motor dies when shifting, 'n it's always the lower shift cable most of the times,....

So I did figure that out and according to my multimeter it works.

 

[Scott Danforth]

Don't confuse a bad lower shift cable for a bad switch. Easy to diagnose

 

[manebeam]

Don't confuse a bad lower shift cable for a bad switch. Easy to diagnose

Okay I will youtube it and see what to look for. Thanks.

 

[manebeam]

It's a $6 switch if it is bad

I’m reaching here but by the off chance do you know what switch from digitech would fit my configuration? I contacted them and was pleasantly surprised they responded already but unfortunately they said they didn’t think they had what I needed.

 

[nola mike]

I’m reaching here but by the off chance do you know what switch from digitech would fit my configuration? I contacted them and was pleasantly surprised they responded already but unfortunately they said they didn’t think they had what I needed.

Disconnect the switch for testing. Still haven't verified spark loss, right? If it doesn't restart when disconnected, that isn't your problem.

 

[Scott Danforth]

Okay I will youtube it and see what to look for. Thanks.

dont look to facetube. most of the info is wrong. look in the stickies on this forum. however a failing lower shift cable will delay its action often causing stumbling and in some cases killing the motor while shifting (use google to search for the string "lower shift cable iboats.com" and you will find lots of reading.

I’m reaching here but by the off chance do you know what switch from digitech would fit my configuration? I contacted them and was pleasantly surprised they responded already but unfortunately they said they didn’t think they had what I needed.

look at the side of your switch, then look at the on-line catalogs on digikey or newark. last time I needed one, it took me about 5 minutes to find what I needed.