Perhaps you got a bad tankful of gas. The gas is so low in octane that the DME is retarding the timing which is the cause of the lack of power and the pinging is just a confirmation that the gas is probably bad.

A block exhaust whether it's the cat or muffler could also be the problem with the low power since an engine is nothing but a pump, pumping air in and pumping air out, but if the pumping air out is blocked, then the amount of air being pumped in is also reduce.

You can remove the 02 sensor and install a compression tester to see what the psi is in the exhaust system.

There's a youtube video on how to do this.

I had an Opel Manta that had a block exhaust and the only way the car would gain speed was if you had the pedal to the floor. The exhaust had a hissing sound, but once I replaced the exhaust the car drove normal.

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