OK all.. Here's a tough one. At least for me!
I've been driving about 120 miles on I-5 a day for the past few days at various times. Sometimes I'll drive up to Davis at 11 in the morning, 3 in the afternoon, and 9 at night.
I noticed that when I take the drive in the daytime (between noon and 5 p.m.) my Mustang pings A LOT... Light acceleration above 65 or 70 MPH will yield serious pinging... Now I know what you're going to say... TIMING. Well, I don't know. Because when I make the drive to Davis in the evening after the weather cools down, I can hit 100 MPH without ANY sign of pinging, even if I accelerate gradually up to that speed. (Yes, six cylinder motors can reach 100... with a lot of work...)
Anyway... Why does heat affect at what point my engine will ping? Does heat affect octane rating? I use 91 in my car, Chevron Supreme... I tried switching gasoline and trying Shell's premium 91 octane with the same problem. My timing is set as per expert advice here on this board and I am quite sure my timing marks are right on the money.
I am thinking it might be vacuum related but what would outside temperature have to do with vacuum? A vacuum test was performed about 6 months ago with textbook results.
Could I need a new thermostat? What the heck is going on here?
I've been driving about 120 miles on I-5 a day for the past few days at various times. Sometimes I'll drive up to Davis at 11 in the morning, 3 in the afternoon, and 9 at night.
I noticed that when I take the drive in the daytime (between noon and 5 p.m.) my Mustang pings A LOT... Light acceleration above 65 or 70 MPH will yield serious pinging... Now I know what you're going to say... TIMING. Well, I don't know. Because when I make the drive to Davis in the evening after the weather cools down, I can hit 100 MPH without ANY sign of pinging, even if I accelerate gradually up to that speed. (Yes, six cylinder motors can reach 100... with a lot of work...)
Anyway... Why does heat affect at what point my engine will ping? Does heat affect octane rating? I use 91 in my car, Chevron Supreme... I tried switching gasoline and trying Shell's premium 91 octane with the same problem. My timing is set as per expert advice here on this board and I am quite sure my timing marks are right on the money.
I am thinking it might be vacuum related but what would outside temperature have to do with vacuum? A vacuum test was performed about 6 months ago with textbook results.
Could I need a new thermostat? What the heck is going on here?