Marine: Boating, Sailing, PWC, GPS and Navigation - Mercruiser Thunderbolt V Ignition Timing Problem

I have been trying to get my 1997 7.4L Mercruiser engine with Thunderbolt ignition into base timing, to time it. I have grounded the purple and white stripped wire, but it will not change the timing (when I ground it I see no change what so ever in the timing). I have checked the continuity of the wire back to the plug and it is good. I checked the continuity to ground and it is definitely grounded. Does anyone have any help as to what may be bad not allowing me to get to base timing, or am I in base timing and something is bad and I am not getting timing advance? I am definitely down on power which is what lead me to check the timing. Any help would be greatly appreciated.

Thanks in advance,

Mike

From a buddy

lastly.. your motor i believe has a TBolt V ignition system in it. which has it's own governing power over ignition advance... basically it'll keep feeding timing until the motor will not gain anymore rpm then it willnot add more... i believe the system is capable of 21 or 22* of total advance... in order to set initial timing you have to ground the system or the computer will compensate when attempting to set initial timing via rotating the distributor... you also have to ground that little purple wire with the white stripe when checking initial timing... this basically disables the ignition advance of the module and puts the system into a "base" ignition mode. lastly for that system it incorporates a knock sensor... SO if the motor begins to ping due to inadequate fuel grade or what not the ignition retards itself to keep the motor from putting a hole in the top of a piston.

My partner and I recently overhauled the our Volvo Penta 350 V-8, and its DuoProp outdrive and also had to upgrade the wiring and replace the non-marine distributer that had been installed by the previous owner. We had a boat dealer do the rewiring, distributer, and outdrive work. We tested the engine and outdrive when we picked it up and the engine ran smooth at idle and at RPM's up to 3 grand or better. We recently put it in the water to do a shakedown and the engine appears to be running smooth with plenty of power, but under a load above 2,000 r.p.m.s I thought I was hearing a rattle/clatter that I am afraid was a marine ping (because of the distributer and timing change) since I've heard marine ping doesn't sound like the low octane ping in a car and this disappears at lower RPM's or without a load. I have a call into the shop, but I wondered since you appear to be knowledgable about marine ping what you thought. One thing, the boat was out of service since July with about 100 gallons of fuel on-board. We filled it with about 50 gallons of premium to try to offset any octane loss though. Thanks again.