5.7L 250hp year 200(4?) no spark.

[clueless75]

*Long story so grab some popcorn and enjoy*

So, last summer my dad and I took out his 21' 2003 Maxum 2100sc with a 5.7L 250hp mercruiser to go camping.

Now, keep in mind this is my father's first boat (story of his first ever docking experience at the bottom), and he has owned this boat since new and has not maintained it very well for half of its life. One year a while back (I think in '05) he took in into a marine shop to winterize it, took it home and let it sit over winter, then in spring he came to look at the boat with a crack in the block. Unfortunately the shop that winterized the engine went out of business (no wonder) so he could not do much about it. He bought a brand new motor of the exact same size and specs (and year I think too), but this time he installed antifreeze coolant for the engine block.

Now, as the story begins, we were going heading across the Strait of Georgia here in BC, Canada when we were about halfway across the strait and the motor suddenly died - instantaneously. No slow deceleration til it died, no preluding alarm, just completely quit when we were going about 40 km/h. We opened up the engine compartment, looked for any obvious signs of failure but to no avail. So, we closed that up and started up the motor, which started normally. We continued on our way and about 3 minutes later, the motor died again, the same as before. We checked for any signs of anything, but nothing was amiss. We turned over the motor again but this time it did not start at all (side tip, the motor died about 2 weeks prior to this, at about the same spot in the strait but my dad was fairly certain he accidentally bumped the kill switch. This time he knew he didn't). We started up the kicker, and putt putted about half an hour to Galiano island and docked up at the ferry dock. My brother called a mechanic and he gave us a few things to check before he came down, which included checking for spark at the coil. There was no spark at the coil, so he came down and checked everything out. Over the next week he would have himself and three other mechanics all trying to figure out what was wrong. They bought a new coil, a new distributor (which really needed to be replaced as there was about a few millimeters of corrosion on each point), and I believe they also did something with the rotor and condenser/point. Anyways, none of them could find the problem and basically told us there wasn't much more they could do with the boat in the water, so we had to take a ferry home, pick up the trailer, take a ferry back, get the boat towed from the dock to the boat launch on the other side of the island, and take the ferry back home. The mechanic was a really nice guy and even let us stay at his Bed and Breakfast for a night when we were travelling around with the trailer. Anyways, ever since the boat got brought home, it has not been touched until today. Over the past year, we ordered a new coil and distributor (specifically for this motor) since the mechanic on the island was only limited to using car parts as there were no marine shops nearby. We also bought a repair manual, and began troubleshooting today. So, following through the step by step process in the repair manual (and steps found on this site under miscellaneous mercruiser information), the engine failed basically every test. It never sparked once from the coil using two different spark testers, and two different coils. Both coils checked out for continuity and voltage, and so did the tach wire, but every single test involving checking the coil for spark failed. I'm thinking that it may be the Ignition Control Module (part number 861253-1) but that is a very expensive and hard to find part, so I wanted to be sure before spending that kinda money on a part that might not even be the problem. I was reading somewhere that an ICM can get fried by hooking up the battery wires oppositely, which my father did do by accident a few years ago, although it ran after and ever since. The engine only has 75 hours on it and hasn't been used very often, just about once or maybe twice a season to go camping and that's it. Also, I recall last summer when it did run, the oil pressure gauge wasn't working and my father said that the tach was faulty sometimes. When turning over the motor today, the tach did not move at all. I'm not sure whether its supposed to move before it starts with this engine, but my older 1975 Merc 850's tach moves when being cranked, so I just assumed it should. Anyways, if anyone has any help, suggestions, or comments before my dad buys a $500 part, that would be very much appreciated! Thanks guys.


UNIMPORTANT: My dad's first ever docking experience did not go well. Here he is, with a brand new and shiny 21' powerboat, coming into the dock. Now keep in mind, he has never, EVER operated a boat before in his life. Anyways, here he is with a boat full of his family, slowly cruising towards the dock. Unfortunately, I guess he believed that the boat would dock itself so the boat just gently taps the dock, at a 90 degree angle, still in gear. Then the dock begins to crack as the boat tries to cut through it, in which it partially does, until he finally put the motor into neutral. Now I thought he was a smart guy, but clearly not. Anyways, lesson learned after scraping the bottom of his boat and destroying a dock.

(pic of old distributor cap)

 

[Scott Danforth]

check to see if the safety lanyard is tripped.

prior to buying parts, you have to diagnose problems

 

[clueless75]

How would I check for that? I don't have the repair manual on me right now to look it up

 

[achris]

The basic Thunderbolt IV or V system is very simple and easy to troubleshoot. Here's a basic picture of the system with all the extraneous bits pulled away. (Don't worry that the module has IV on it, V is the same, but a slightly different program)






This is the basic system required to make your Mercruiser engine run. If you have Thunderbolt V and it has a knock sensor, just unplug the module and you will have what you see here.

What we expect to see at the various points. At Coil+ we want to see +12v whenever the key is ON. At white/red wire on sensor we also want to see +12v. This is the supply that the sensor needs to do it's job. At white/green wire on sensor is where the action takes place. We need to see a constantly up and down between 5v and 0v. These pulses tell the ignition module to fire the coil and the coil produces a spark, which it feeds to the centre terminal of the distributor cap and onto the rotor, then back out on one of the edge terminals of the distributor cap to a spark plug via the HT lead. The function of the shift interrupt switch (MC-1, R, MR, Alpha drives only) is to ground the white/green wire and stop the stream of pulses to the module, hence, no more sparks until the switch is released, which when the shift system is working properly should be around 1/2 second.

Now, some of the things that can cause the system to stop producing a spark are....
Bad grounds. This is probably the most common source of trouble. Check all grounds are good back to the engine block, that includes the distributor. Make sure it has a wire that electrically grounds it. Being bolted to the engine is not enough, trust me, I have seen (and was the one who fixed) a heat fault where the distributor lost proper electrcial continuity to the engine block!

Faulty tacho - Disconnect the grey 'tacho feed' wire and recheck.
Faulty shift interrupt switch - Disconnect the switch and recheck.
Faulty sensor - disconnect the white/green from the sensor and tap it against a good ground a few times a second. This simulates the pulses the module is expecting, and should produce a spark. Just on checking spark, pull the main HT lead from the centre of the distributor cap and plug a spare spark plug into that. Lay it on a convenient spot on the engine block, ensuring good contact, so you can see the gap. That eliminates the cap and rotor as possible faults. You should see a healthy blue spark. Yellow is a weak spark.

What to check if any test points shows up bad.
Coil purple wire. No 12v? Check fuses, circut breaker, key switch, harness connections and lanyard safety switch (also known as 'Dead-man switch'). Even if there is 12v on the coil, I would also pull the plug from the module and check for voltage on the purple wire directly.
Sensor white/red wire. No 12v? Disconnect the white/red wire from the sensor and recheck. Still no 12v, check that wire back to the module, if ok, bad module (assuming 12v is on the purple wire) If disconnecting the white/red wire brings the voltage on that wire back up to 12, then change the sensor.

One last thing to check with a 'no spark' condition. Pull the distributor cap off and make sure the rotor is down on the shaft properly and turning when you crank the engine. More than one good ignition system has been tossed due to the distributor gear being stripped.

I hope this helps find the source of your problems.

Chris........

 

[clueless75]

Thanks for the help guys, but we bought a new ICM, put it in, and it started right up. Thanks for the extensive response Chris! Hopefully it will help others with the same problem. Happy boating everyone!