thunderbolt iv no spark

chartersj

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I have been working on a project boat, i have replaced the block and trying to figure out why i am not getting spark. While cleaning connections i broke a stud off the coil, so i have a new one on it now. I have followed the trouble shooting guides which lead me to a bad coil, or bad ignition module. So i have a new coil, and i bought a module off a known running boat. I have 13+ volts on both side of the coil with the key on. I have 12.8 volts to the White/red going between the module and distributor. I dont get any spark on the white/green from distributor to ground. I am only getting 4.5 volts on the purple wire on the starter which has me puzzled. Also i have a purple wire close to the carburator with a black connector on the end not going to anything with 12+ volts on it with the key on. however i dont think it was connected to anything before. Any thoughts? How can i jumper out the kill switch?
 

achris

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To remove the shift interrupt switch from the system, just remove the white/green that goes from the switch to the sensor module in the distributor. 12 volts on both sides of the coil is correct. As the coil has a very low resistance (about 0.7Ω) the 12 volts will appear both sides. There shouldn't be a purple wire on the starter. What is the engine serial number so I can get the right drawing. Electric fuel pump or mechanical?

Here is a link to an article I wrote on the TB systems. You may find it useful.

How Mercruiser Thunderbolt ignition systems work

Chris....
 
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chartersj

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Nice write up! My original module is the 3rd one that bolts to the distributor, and the one i bought is the plate mounted...any difference electronically?
I ohm tested the shift interrupter switch and it tested ok, but also had it disconneted for testing. I am wondering if the safety lanyard switch could be the problem and how to jumper that out, And the motor has an electric fuel pump which is no good and looking for a replacement at the moment. I used a 4.3 out of a truck so im not sure if the serial number off that would be any help. The number on the new block is 14099090M. The one on the old block is 10224535. There was also a tag that read F015297.
 

achris

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Nice write up! My original module is the 3rd one that bolts to the distributor, and the one i bought is the plate mounted...any difference electronically?
No difference at all.

chartersj said:
I ohm tested the shift interrupter switch and it tested ok, but also had it disconneted for testing.
I always do that. It may check out ok, but I have seen them resistive and cause problems. Same with the tacho feed wire, remove it for testing purposes.

chartersj said:
I am wondering if the safety lanyard switch could be the problem and how to jumper that out,
If you have 12volts at the coil, the safety switch is working fine.

chartersj said:
And the motor has an electric fuel pump which is no good and looking for a replacement at the moment. I used a 4.3 out of a truck so im not sure if the serial number off that would be any help. The number on the new block is 14099090M. The one on the old block is 10224535. There was also a tag that read 0F015297.
Always good to keep the orginal engine serial number, even with the new engine, it tells a lot about the rest of the engine too. From that serial number I can tell you it was a 1993 '4.3LX' engine, balance shaft Gen II, (and that's the engine, not the drive), with a 4bbl Weber 9600 carb (heat stove choke).


Here is the connector I'm not sure where it goes

???

Chris....
 
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chartersj

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[/QUOTE]


???

Chris....[/QUOTE]

Sorry the picture didnt work the first time. This is the connector near the carburator that im not sure where it goes but it has 12+ volts on it.
I jumpered out the safety lanyard switch and i have the same results as well.
 

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achris

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That is for the electric choke when a Weber 9666 or Mercarb 2bbl carb is fitted.
 

chartersj

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That is for the electric choke when a Weber 9666 or Mercarb 2bbl carb is fitted.

ok thanks. I am still struggling to find out why i do not have spark. New plug wires and spark plugs.
Also, In my manual it shows a purple/yellow wire going to the starter...which i am only getting 4.5 volts on
 

achris

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Check for spark from the coil. Pull the HT lead from the centre of the distributor cap, put a spark plug in it and lay the plug on the engine block. Then check for spark.
 

achris

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That purple/yellow wire is the feed for the fuel pump while the engine is cranking. Once the engine starts the oil pressure switch closes and the pump is powered via the switch. 12 volts will appear on that wire as a result. Having 4.5v on that wire is strange. It could indicate a faulty oil pressure switch.
 

chartersj

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Check for spark from the coil. Pull the HT lead from the centre of the distributor cap, put a spark plug in it and lay the plug on the engine block. Then check for spark.

I don't get any spark from the coil or when I strike the white/green on ground. I was thinking the oil pressure switch was fine because while cranking I will not get an alarm until I stop cranking the engine over for about 7 seconds. I have jumpered out the lanyard kill switch, I have changed connections on all the ground wires I could find. I was wondering does the ignition module have to be mounted to get ground? I just have it laying on the top of the motor for testing because I have two of them. And again I have a brand new coil installed as well.
 

chartersj

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I put a ground on the plate the module is mounted to and still no spark from coil. I still have 12 volts to the white/red wire from distributor
 

achris

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If you have a multimeter, measure the voltage on the white/green wire. It should move between 0v and 5v as the rotor 'window' passes the sensor. If you have the 0 and 5v swing, then the module is probably faulty.
 

chartersj

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If you have a multimeter, measure the voltage on the white/green wire. It should move between 0v and 5v as the rotor 'window' passes the sensor. If you have the 0 and 5v swing, then the module is probably faulty.

Thanks, just tried this out and i cannot get any voltage on the white/Green wire
 

Pete104

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There have several versions of the sensor in the distributor. How many wires do have on yours?

I went through this same scenario this week. I had an original 2 wire sensor without the thru bolted ground wire. No spark. Went thru the tree a few times. Had the 12 v on red wire (efi) but no spark on the green. It had corrosion on it so I didn't feel bad about throwing a sensor in it. Got spark in gap tester. Hit the key it while moving throttle starts very rough. Doesn't sound well. Tried to idle & it quit. Thru the tree again no spark on green wire. Threw a coil at it. Bingo. Just for giggles put the old sensor back in it. No spark. Switched back & all was good.

If you decide you want to try the sensor, install it as recommended. Not that you wouldn't, just saying. Then make sure timing is still good.
 

achris

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Thanks, just tried this out and i cannot get any voltage on the white/Green wire

Remove all (both) wires from the white/green terminal on the sensor. Make sure you have 12v on the white/red wire (still connected) and try the white/green terminal with a multimeter. Turn the engine until the 'window' of the rotor is open for the sensor (the sensor not 'blocked'). Take a thin peice of steel (like a 6" engineers rule) and pass it through the window. You should see a 0 to 5 volt swing on the white/green terminal. If you don't, check the ground, if that's ok, replace the sensor.

Chris.....
 

chartersj

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Remove all (both) wires from the white/green terminal on the sensor. Make sure you have 12v on the white/red wire (still connected) and try the white/green terminal with a multimeter. Turn the engine until the 'window' of the rotor is open for the sensor (the sensor not 'blocked'). Take a thin peice of steel (like a 6" engineers rule) and pass it through the window. You should see a 0 to 5 volt swing on the white/green terminal. If you don't, check the ground, if that's ok, replace the sensor.

Chris.....

Just did what you said. Im not getting any voltage on the white/Green with nothing connected. I still have 12.5volt on the white/red. Looks like I am going to need a sensor. Thanks for the help!
 

achris

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Make sure the ground for the sensor is good.
 

chartersj

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Make sure the ground for the sensor is good.

Yeah the ground was good on that one too. I have a new rotor, cap and sensor on the way now. The sensor was the newer 3 wire sensor and looks fairly new, I broke the rotor trying to remove it off the shaft...
 

achris

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Yeah the ground was good on that one too. I have a new rotor, cap and sensor on the way now. The sensor was the newer 3 wire sensor and looks fairly new, I broke the rotor trying to remove it off the shaft...

OK, sounds like the sensor has failed. Yeah, the rotors are loctited on. Get some Loctite 222 for the new one.

Chris.....
 
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