what could be causing my 99 gt to spark knock if I dont run 93 octane fuel, any thing lower under wot spark knocks? I dont think its tuned cause the sct I got with it was locked to another car? Only mods are exhuast, filter, and rear end. How is timing adjusted, could that be an issure?

 

i dont know about sct, but most tuners tune for 93 octane fuel. check the sct website for the requirements

 

Does your speedometer read correctly? If so, and there's no Speed-Cal or other added device, then you do have a custom tune loaded--that's the only way to correct the speedometer with the 4.10 gears. And it may well be that it's a 93 octane tune (timing is adjusted in the tune).[/align][/align]Just run 93 octane, it's only $3.00 a tankfull more...[/align]

 

No the speed-o is 10 mph off. The guy said that he used the xcal on the other stang he had and it needed to be unlocked and that it wasnt used on mine. But I didnt know if it had a shop tune on it because these cars should run on under 93?

 

It's not unheard offor compression ratio to rise a bit on higher mileage engines, as carbon builds up in the combustion chamber--however usually it's just a little bit, not enough to force the use of premium fuel on a car designed to run swill.[/align][/align]Oneway to know for sure would be to have an SCT shop read the tune and "see what they can see"...[/align]

 

not quite true... the ford obd2 scanner that they use can correct things like this.

 

on my o3 the ids( ford scan tool) would only let me modify the gear ratio in a narrow range (3.25-3.29) came with 3.27 gears. this was due to emission regulations, this may or may not be the same for his 99

 

[/align][/align]You are correct, however the Ford tool does reflash the "tune" while doing this--it just doesn't change any of the engine control settings in the process--just the gear ratio setting...[/align]