Engine Dies When Hot

[Crownline290]

I have a 2003 Crownline 290 with twin Mercruiser 5.0L carbureted 220hp engines with Alpha One drives.

Been having an issue with my starboard motor for quite some time. The motor runs great for about 20-25 minutes, and then it randomly shuts off. It will then start, rev and shut off. The next morning as soon as it is cool again, the motor will start right up again like nothing ever happened.

I have replaced the sensor under the distributor cap, the coil, and just changed the fuel pump today. Was hoping that would fix the issue, but I just took the boat for a ride and the same thing happened.

While it was in the no-start condition, I tried bypassing the oil pressure sensor and it still wouldn't start. I then disconnected the wire on the shift interrupter switch and it fired right up. Oddly enough, unless I bypass both the oil pressure sensor and disconnect the shift interrupter switch, the boat won't run.

What gives?

I'm thinking of replacing both parts.

Any advice is much appreciated.

 

[alldodge]

Sounds like a spark issue, but lets do some testing first.
What is your motor serial number?

 

[Crownline290]

Sounds like a spark issue, but lets do some testing first.
What is your motor serial number?

I’ve looked everywhere for a serial number and can’t find one. Where is it usually located?

Thanks!

 

[dubs283]

I’ve looked everywhere for a serial number and can’t find one. Where is it usually located?

normally located on the plastic cover over the flame arrestor, i've often seen the number(s) missing from that location

mercruiser oem engines have a metal tag with serial # stamped in it riveted to the block just above the starter (stbd side aft on a gm sterndrive)

lucky for you there is a parts room located right next to your stbd engine, after proper troubleshooting of the ignition and fuel system simply swap the suspected part(s) from the other engine, saves time and money

 

[Crownline290]

No luck on the serial number. I guess these engines are not original and we’re replaced at some point.

Any ideas on why the boat when hot will run only when I jump the low oil pressure sensor and unplug the shift interrupter switch at the same time?

 

[alldodge]

Without a serial number and being a 2003, would it be a Carb?
If it is a carb motor then jumping the fuel pump should have no effect

Most likely a TBV ignition

Something is getting hot like the the ignition module. If it is a TBV, when it won't start, and before doing anything else run through the chart

 

[Crownline290]

It’s a carb. I’m not jumping the fuel pump, I’m jumping the low oil pressure sensor. I’ll run through the chart and see what happens.

Thanks.

 

[alldodge]

It’s a carb. I’m not jumping the fuel pump, I’m jumping the low oil pressure sensor. I’ll run through the chart and see what happens.

Thanks.

Understand, but the oil pressure switch turns the fuel pump off if oil pressure is low, otherwise during starting, it comes from the starter post

 

[Crownline290]

Interesting. Maybe that explains why the motor will also run if I hold the key in the crank position, but then die when I let off. I’ll report back as soon as I run the tests. Hopefully this thread will help someone one day.

 

[alldodge]

Maybe that explains why the motor will also run if I hold the key in the crank position, but then die when I let off. .

Would be nice to know that tid bit of info.
THis says it may be as simple as the key switch

 

[Crownline290]

I just thought last night about how it would stay running if I held the key in the crank position. Have you ever seen key switches only kill the engine once it was running for over 20 minutes?

 

[alldodge]

Anything is possible, just not very likely

The below is what happens when a key switch goes bad or wire on RUN side is loose
No 12V when key is ON to the coil
Have 12V when key is cranking to the coil

 

[Crownline290]

Appreciate all the advice. I’m going to troubleshoot this weekend and report back. Hopefully with my volt meter and a cold one I’ll get to the bottom of it.

 

[Crownline290]

So I went through the thunderbolt troubleshooting and everything checks out. Took the boat out again today. Ran great for 10 minutes, then started stalling out. Would run for a few minutes and stall, run for a few minutes and stall, all the way back to the dock, which was about 15 minutes.

When I got back to the dock, it started back up and ran continuously at the dock for about 20 minutes. I then took it out again and it ran on plane for another 20 minutes. As soon as I got back to the dock it stalled and wouldn’t start again. Everytime time I tried to start the engine it would rev up and then stall.

I don’t know what else to do at this point - new coil, new fuel pump, new 3 wire sensor under the distributor cap. Did a continuity test of all the ignition wires and they check out.

I think next step is to replace the low oil pressure sensor and see what happens.

I’m almost ready to give up.

 

[alldodge]

If it dies out with a gasp then its fuel or weak spark, mostly gas. It it dies quick (like turning key off) then its electrical

 

[Crownline290]

It’s like turning the key off.

 

[nola mike]

Did I miss the part where you checked for spark when the engine won't start?

 

[dubs283]

Did I miss the part where you checked for spark when the engine won't start?

agree, have not seen that

aside from changing parts and running the engine i don't see much troubleshooting going on here. its in your interest to check for spark immediately upon the engine dying

as i stated before, there is really no need to purchase a suspected failed part, just swap from the good running engine. this is helpful especially if you are merely replacing parts without actually checking them

 

[Crownline290]

Just wanted to thank everyone for the help. It turns out that it was the main harness. There were a few wires in there that needed to be re-spliced. Hope this helps a fellow boater one day.