overclock CPU powermac MDD FW800, dead L3

[redstudio]

I have overclocked all my MDD FW400 macs with dual ring CPUs from 1.25 to 1.5ghz L3 2mb with no issues. I increased the voltage to 1.60v,
stable for years. very happy with these.
Different story for MDD FW800 with three-ring CPU. even just changing from 1.4 to 1.5 ghz gave me L3 loss, but how is this possible?
Is there a different process to overclock these CPUs without problems while maintaining L3?
To eliminate the heat problem I recently bought a 360 liquid heatsink which I adapted to the Mac heatsink, it works very well.
one of the three ring CPUs I managed to reach stable at 1.67 ghz (1.75 never managed to start mac even with different voltages..)
but you can't see it from L3. the system tells me in information "diagnostic failed". I would love to have the L3 on this one.
Has anyone had any problems with L3 on 3-ring CPUs? 3 CPUs on which I tried overclocking, both 1.25 and 1.4 GHz always lost L3..
I read on a site that to get the L3 back you need to increase the L3 voltage but no indication of how to do it,
Can anyone kindly help me?

[hoovers@dawn]

What os are you using? OS X or unsupported os9lives install for fw800 models? could it be the firmware? Or are you overclocking 3ring cpu card on fw400 models?

[redstudio]

the FW800 three-ring CPU I kept the same computer.. in the past I tried to experiment with exchanging the CPUs but none of them started, neither the FW400 with three-ring CPU nor the FW800 with two rings..
I let this go...
3 FW800 CPUs modified to 1.5, originally 1.25 and one 1.4ghz, different computers always FW800, all three lost L3 both with OS9
(modified to run on these machines.) that with OSX (10.4 and 10.5)..it doesn't work for me,
possible? has this ever happened to you? Is there a way to solve and review L3?