Thunderbolt V Ignition losing spark

[Chris H]

Hello,
im hoping someone will be able to help me out. I have a maxum 2300sr with a 5.0 mercruiser alpha 1 gen 2. Boat ran great when i winterized it but now the issue is, i have great spark for about 2-3 seconds when cranking then it dies out. I have a spark tester in line with the coil and distributor and see it fade to barely lit. I replaced the coil, cap, rotor, distributor sensor and sill having the same issue. I disconnected the white/red wire from the dist and have 12v. I have gray wire at the tach is showing ground but if i disconnect there is no change. Also should my + and - at the coil be showing 12v? Are there any tests i can perform to diagnose the Ignition control module? Any help would be greatly appreciated.

Thank you in advance!
Chris

[Gugi47]

By replacing the coil, cap, rotor. Yo just norow down to the problem.
Must of the time is the coil what do this things, but you replace that, so the only one left is the Ignition Module.
Wait for some more opinions.
My only suggestion is, if you have to buy a Module, don't buy aftermarket one, they are junks. Quiksilver is o good choice.
Good luck.

[mmwjr]

Originally Posted by Chris H

Hello,
im hoping someone will be able to help me out. I have a maxum 2300sr with a 5.0 mercruiser alpha 1 gen 2. Boat ran great when i winterized it but now the issue is, i have great spark for about 2-3 seconds when cranking then it dies out. I have a spark tester in line with the coil and distributor and see it fade to barely lit. I replaced the coil, cap, rotor, distributor sensor and sill having the same issue. I disconnected the white/red wire from the dist and have 12v. I have gray wire at the tach is showing ground but if i disconnect there is no change. Also should my + and - at the coil be showing 12v? Are there any tests i can perform to diagnose the Ignition control module? Any help would be greatly appreciated.

Thank you in advance!
Chris

Welcome aboard

The + terminal on the coil should read 12V to ground and the - terminal should pulse between 2V and 8V approximately.

When you say distributor sensor you are referring to the internal trigger sensor, correct. The newer sensors have three wires instead of two is this what you new one has and did you connect it correctly? If I recall the third wire is connected to ground.

[Chris H]

Originally Posted by mmwjr

Welcome aboard

The + terminal on the coil should read 12V to ground and the - terminal should pulse between 2V and 8V approximately.

When you say distributor sensor you are referring to the internal trigger sensor, correct. The newer sensors have three wires instead of two is this what you new one has and did you connect it correctly? If I recall the third wire is connected to ground.

Yes, the internal trigger sensor in the distributor has 3 wires. white/red, white/green and black to ground post on engine block. I should also mention i have tach signal while i have spark and no signal when spark dies out. If i stop cranking and try to crank again without turning the key to the off position no spark after the initial drop out. If I turn the key off and then back on again it will spark for a few seconds every time. As for the coil, i have 12v on the + terminal and im about to go check the - terminal for pulsing signal.

[mmwjr]

When you loose spark verify there is 12V on the purple wire on the back of the ignition switch. If no power the ignition switch is bad.

[Chris H]

Originally Posted by mmwjr

When you loose spark verify there is 12V on the purple wire on the back of the ignition switch. If no power the ignition switch is bad.

I have 12v on the purple wire which drops down to 9.5v when cranking. + terminal of coil is 12v, - term is a pulsing signal. I have spark for approx 3 seconds and lose spark and tach signal at the same time. Should have have a pulsing tach signal on the grey wire leaving the ICM? Also if i disconnect the white/green wire from the dist and with the ignition on strike the white/green from the ICM to ground rapidly, i dont see any spark in my spark tester. Im leaning towards a ICM, going by the troubleshooting flowchart for TBV ignition systems i found on this forum.

[Gugi47]

Originally Posted by Chris H

I have 12v on the purple wire which drops down to 9.5v when cranking. + terminal of coil is 12v, - term is a pulsing signal. I have spark for approx 3 seconds and lose spark and tach signal at the same time. Should have have a pulsing tach signal on the grey wire leaving the ICM? Also if i disconnect the white/green wire from the dist and with the ignition on strike the white/green from the ICM to ground rapidly, i dont see any spark in my spark tester. Im leaning towards a ICM, going by the troubleshooting flowchart for TBV ignition systems i found on this forum.

Mike ask you if you have 12V. at the purple wire after you lose the spark.

[Chris H]

Drops from 12v to 9.5v while cranking and yes i still have it after i lose spark.

[mmwjr]

Well I’m sorry to say but it’s seems to be the ICM.

[Chris H]

Originally Posted by mmwjr

Well I’m sorry to say but it’s seems to be the ICM.

Thats what im thinking, i appreciate your time and help. I will order an ICM and post again after i replace with new one.

[mmwjr]

Can you buy just the ICM or do they only sell the ICM along with the knock module? From what I recall the knock module is connected to the ICM by a purple/white wire and when triggered the knock module puts the ICM into a limited rpm mode but this is not you issue so it truly sounds like its an issue in the ICM.

[Chris H]

Originally Posted by mmwjr

Can you buy just the ICM or do they only sell the ICM along with the knock module? From what I recall the knock module is connected to the ICM by a purple/white wire and when triggered the knock module puts the ICM into a limited rpm mode but this is not you issue so it truly sounds like its an issue in the ICM.

I believe i can purchase just the ICM for around $500 some some sites. Im trying to locate one now that i can possibly have by the weekend.

[Chris H]

Originally Posted by Chris H

Thats what im thinking, i appreciate your time and help. I will order an ICM and post again after i replace with new one.

I gave it one last try this morning, while ordering the ICM from a marina by me. The mechanic asked me to try this before buying an ICM since they are $550 and non refundable. He had me disconnect the harness going to the front of the boat. Then hook up from batt to coil, 12v to + on coil and neg on - on coil and jump out the upper starter solenoid and she fired right up. Replaced the starter solenoid with a new one i already had for trim unit and all is good.

[Gugi47]

So you up in running without harness. Right?
Woow, now start the fun. Find where is the problem in the harness.

[mmwjr]

What do you mean by upper starter soleniod? Slave soleniod next to engine breaker? Or soleniod on top of the starter? Either way I don’t see have either soleniod would cause ignition to die. Now if you have an electric fuel pump the starter soleniod can prevent power from being applied to the fuel pump.

[Chris H]

Originally Posted by mmwjr

What do you mean by upper starter soleniod? Slave soleniod next to engine breaker? Or soleniod on top of the starter? Either way I don’t see have either soleniod would cause ignition to die. Now if you have an electric fuel pump the starter soleniod can prevent power from being applied to the fuel pump.

Yes, slave solenoid next to breaker. I do have an electric fuel pump which was getting 12v when cranking. The mechanic said he had seen it before and bet me it was likely the key switch or the slave starter solenoid. I gave it a go as he has plenty more experience than i do with boats and i had the solenoid already from a spare for my trim. I replaced it and it worked. I plugged the harness back in, operates from key switch. Either way, im extremely happy i dont have to buy a harness or ICM which is what i was purchasing yesterday morning when i spoke to this guy.

[mmwjr]

Guess I’m really confused as this now sounds like a fuel issue and not spark. Additionally the slave solenoid has nothing to do with fuel pump power. The fuel pump gets power from the starter solenoid while cranking and once started there is an oil pressure switch that closes under oil pressure that then provides power to the fuel pump.

Anyway glad she’s running.

[Chris H]

Originally Posted by mmwjr

Guess I’m really confused as this now sounds like a fuel issue and not spark. Additionally the slave solenoid has nothing to do with fuel pump power. The fuel pump gets power from the starter solenoid while cranking and once started there is an oil pressure switch that closes under oil pressure that then provides power to the fuel pump.

Anyway glad she’s running.

Thank you for your help. Its a bit confusing to me as well.. Especially since i tested the ICM with a spark tester and grounded the white green from the module 3 times per second and didnt see a spark. Fuel was not an issue, i had the initial squirt when i put the throttle forward. But it didnt start so i couldn't see if it was squirting out the jets in the carb until after it was running. It runs, idles perfect. Im just happy to have it going. I need it out of my backyard asap.