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Old 12-02-2009, 09:34 AM
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Default mercruiser ignition identification - thunderbolt ??

I'm trying to identify what ignition system I have on my motors. Boat has twin 4.3L V6's with Alpha drives. One motor is a 1998. The other is a 2004. They are not fuel injected and have carburetors. The 1998 has an ignition module bolted on the exhaust manifold. The newer motor only has a small module mounted on the distributor. I think the timing is not right and know there is special timing procedures for the thunderbolt ignition systems. Any help would be greatly appreciated. Thanks

One other quick question. The 1998 motor is a LX. The 2004 motor is a LH. What does this mean. Thanks again.
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Old 12-02-2009, 09:48 AM
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On cars, you disconnect the "spout" wire, and the timing reverts to base timing, which is then adjusted. Those systems use the default timing curve in a GM module, which adjusts the timing with rpm only. Depending on the module, there is electronic timing advance from the module even at idle. disconnecting the spout wire eliminates this electronic advance.
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Old 12-02-2009, 11:40 AM
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My 1994 Thunderbolt IV is 8 deg BTDC at idle. I have seen procedures where you adjust max timing at a higher rpm. Mine is (I believe) 32 deg at 3000 rpm's. I used 8 deg at idle for mine and left everything hooked up and it runs perfect.
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Old 12-03-2009, 05:03 AM
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Thanks for the replys. How do I know if I have the thunderbolt IV or V.
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