Been having intermittent pinging problems for months on my wife's '94 MX5. Eventually we realized it only pinged badly when using fuel from a particular local station. The differance is quite obvious, with this fuel, it pings disturbingly pretty much right through the rev range, fill up somewhere else & it's fine. The motor has done 120K, and is in overall good condition, I have not checked timing to see if it has been "tweaked" at all.
Who can I call to get a spot check made? Looks like they are topping up with kero or acetone or something.