Engine intermittently cutting out

[cimy3]

1989 Mercruiser 5.0L Alpha One in a Thompson 240.

Here is my history. I had transom work down. After getting boat back and a sea trial, it needed a shift adjustment. After the shift adjustment, the engine will cut out at various RPMs in forward. It is very haphazard...it will do it one day, but not the next. It acts like the key was turned off. It doesn't hesitate, shake, sputter or cough.

When it cuts off and I am fast enough to put the remote shifter in neutral, the engine will keep running...as if there was no problem. Otherwise, it just stalls like someone yanked a kill switch.

Also,the engine starts easily and idles smoothly.

Where do I begin my search?

Thanks for your help.
Ray

 

[Bifflefan]

Re: Engine intermittently cutting out

I would look to the shift interupter, or a loose wire.

 

[Bondo]

Re: Engine intermittently cutting out

After getting boat back and a sea trial, it needed a shift adjustment. After the shift adjustment, the engine will cut out at various RPMs in forward.

Ayuh,... I agree,... lower shift cable, or the shift switch...

 

[cimy3]

Re: Engine intermittently cutting out

Thanks for the ideas. I was thinking the shift interruptor switch.

So, with the boat on the trailer and not running, I shifted (with remote) into forward (just enough to engage). The shift interrruptor looked fine. Then, I moved the throttle to about 3/4 wot and the roller on the y-plate was up on one of the ears.

After all that I read, this seems wrong.

How can I adjust it?

 

[cimy3]

Re: Engine intermittently cutting out

Can I adjust the lower shift cable to keep the roller from moving while moving throttle towards wot?

 

[81 Checkmate]

Re: Engine intermittently cutting out

Have you tried to just unplug your shift interrupt wire and see if it still does it? It should be the green/white wire going to the dist from the switch.

 

[Don S]

Re: Engine intermittently cutting out

You can't check the shifting with the engine not running. If the dogs are on the high spot the interrupt switch will engage, even if everything is perfect.

 

[cimy3]

Re: Engine intermittently cutting out

OK. So, I decided to go test the shift interruptor switch theory, well didn't get very far with that test! While in neutral and waiting to get warm....engine shuts down (just like the other day). So, while leaving the key in the on position (didn't touch it), I tested the coil....12.32 volts on both sides of the coil. Is that normal?

After testing the coil, I did not turn the key off, tried to restart without turning key to off and it started right up again. Well, it died about 5 minutes later. Tested the coil again and still have 12+ volts on both sides. So, I looked down carberator and it looks like it is wet with fuel.

Once again, I restarted it and it never quit within 20 minutes, so I called it quits for the night.

So, can you point me in a direction now to test?

Thanks, Ray

 

[dubs283]

Re: Engine intermittently cutting out

definitely an intermittent problem!!

have you looked under the dist cap?? - if you have/when you do, do you notice a lot of rust on the sensor??

 

[Lyle29464]

Re: Engine intermittently cutting out

need more testing. The 12 volts on each side of the coil is normal if your points are open.
The shift switch could have shut you down if you moved the gear shift or it vibrated closed. That would have dropped the voltage to zero on the coil unless it opened back up while you were checking things. you really need a load on the prop to test the switch. My guess is your lower cable just a hair off.

some one said unhook it to test. very good idea.

 

[cimy3]

Re: Engine intermittently cutting out

So, since I last posted, I did the following items...

1. Check under distributor cap, looked good, but, I cleaned all the contacts anyway.

2. I put the boat in the water and adjusted the shift cable. It shifts smoothly into forward and reverse with no problems....doesn't kill the engine going into or out of gear.

3.Next, I disconnected the shift interrupter switch...started no problem...guess, what, the engine died within a minute of running. Guess, that is not the problem. So, without turning the key to off, I checked the coil. I had 12 volts to it. So, then I checked if fuel was going into carb. Had the wife, push throttle forward. Nice spay of fuel from both jets.

4. For giggles, I checked the spark to the coil....nice spark!


5. Started the boat again (while tied to the dock) and for the next 15 minutes it would act like someone was pulling the kill switch at different intervals of running.

6. Kept checking coil again and still good.

7. About ready to pack up and go home, but I figured one more try to see if it would stay running...ran at the dock for 15 minutes never cut out. So we head out onto lake.

8. Cruised the canal to the lake it died once, started right back up, then never did it again the rest of the time out on the lake. I had it at wot and in gear in idle and at every throttle position and the engine never cut out...strange!!! Came back through canal to dock and the engine did not die!

Any pointers on what to check now?

Thanks, Ray

 

[Don S]

Re: Engine intermittently cutting out

Make yourself a jumper wire and jumper from the battery + terminal to the coil + terminal and see if it stays running. This will bypass the complete wiring system from the engine to the helm and back. This is just a test to isolate systems, not the final answer.

 

[cimy3]

Re: Engine intermittently cutting out

Thanks DonS. If it stops raining here, I will try it today. Thanks for helping me isolate the issue.

 

[cimy3]

Re: Engine intermittently cutting out

Well, I made the jumper wire and it still quit.

So, I found the electrical trouble shooting form and tested the WHT/RED Terminal on Distributor...had 12 volts.

Next, I need to do a spark gap test from coil tower to ground. Don't have one, so I need to see if I can borrow/buy from a local parts store.

At least now, I with the help of others on this forum, have it narrowed down to the area of problem (I think)...either the ignition sensor in distributor, ignition coil or ignition module/Amplifier.

Am I on the right track?

Thanks for the help.
Ray

 

[dubs283]

Re: Engine intermittently cutting out

either the ignition sensor in distributor, ignition coil or ignition module/Amplifier.

Am I on the right track?

in the case of the sensor, 99.9% of the time they either work, or they don't - rarely do they cause an intermittent issue, i will say though unless you have the latest style OEM sensor it is in your best interest to replace it

a bad/weak coil can heat up and cause a weak spark/lack of spark, check it by feel to see if its really hot when the engine acts up

the ignition module is the most expensive part and like the sensor, it usually either works or it doesn't - the wire harness can also be an issue with it, check the connections for corrosion/looseness

 

[cimy3]

Re: Engine intermittently cutting out

Dubs283...coil is not hot when it acts up. Already, checked the wiring harness for corrosion/looseness and it is good in that sense. Thanks for your insight.

 

[cimy3]

Re: Engine intermittently cutting out

Well, I was able to pickup a spark gap tester... I am going to continue my steps tonight in the troubleshooting tree diagram. I guess, I need to test it when the engine runs, then shuts itself off, while leaving the key in the on position. Sound right?

 

[81 Checkmate]

Re: Engine intermittently cutting out

Yep test it when it fails! That way you can pin point the problem.

 

[cimy3]

Re: Engine intermittently cutting out

Well, I must have scared the gremlin in my electrical circuit. I ran the boat for a total of one hour in two separate time frames (half hour each) and the boat never quit. I turned it off a few times in each interval and it restarted with no problems. This is starting to get very frustrating. Well, I will try again tomorrow...nothing like wishing it would act up!

 

[cimy3]

Re: Engine intermittently cutting out - Final Update

Re: Engine intermittently cutting out - Final Update

Well, I believe I finally figured out my issue. It was the ignition sensor in the distributor...finally was able to find using the flow chart after it cut-out. It's been a couple of weeks now and it, knock on wood, has not had an issue. Thanks for all of you insight and direction.
Ray