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Discussion Starter · #1 ·
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?
 

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I was having some pinging problems that turned into a serious pining problem when the engine got hot. Come to find out that I needed new plug wires. I don;t know why, but they acted worse and worse the hotter it got. It wasn't near so bad at night or in the morning as it was during the day.
 

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Discussion Starter · #3 ·
I just slapped on new Accel 8.8 wires... I'll try some Autolites today I suppose as well...
 

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The heat is just making it ping easier, you are probably on the ragged edge of pinging when it cool. I would back of the timing a couple degree's.
 
G

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im gonna go with what midlife said,you also need to make sure your vac advance is properly adj
if you have that type. air/fuel mix+ bad gas+carbon build up/comp+temp= ping,ping,ping
make sure the heat range on the spark plugs is right for your car!
Dave
 

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If you have time one day, do an afternoon run and experience the pinging, then bring it home and pull a plug and look at it. Do the same for an evening run. Post what you observe.

I'll bet the engine runs hotter (coolant temp) during the day...if so, you're heat soaking the carb more as well as raising the temperature of the inlet air, which makes it harder for the fuel lower it adequately by absorbing the heat as it vaporizes (and the fuel isn't as dense because it's been heated up as well)...

There ar e a lot of nuances to these things...take it from a bracket racer who spent many years figuring out how to keep an ET within .05 seconds from day to night.

I agree with the advice to back off the timing until the daytime pinging goes away....that kind of rattle you don't need....you could experiment with disconnecting the vacuum advance and running through the scenario; it's possible that the vacuum advance plate is sticking and not backing off when you throttle up. n
 

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I agree with most of the other posts.The 4 main contributers to pinging are Timming(total advance),Fuel mixture(Lean),Combustion chamber temp and also carbon buildup.I don't agree with MIDLIFE on this one -"Running rich means pinging"? Running rich is cooler means no pinging.Running lean is hotter,Means Pinging.
 

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You're right, of course. When I first wrote the post, I said it was leaner. But air temperature means the air is less dense, and with constant fuel added, that means the engine would run richer. Cam pointed out that my assumption of the fuel is wrong: it leans out too, and more so than the air due to temperature.

Apologies, and thanks for the corrections.
 

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Discussion Starter · #10 ·
Next week I'll try disconnecting the vacuum advance and see what happens! I'll also check out the spark plugs. I appreciate all the advice...

My engine specialist has an oxygen sensor that he stuck in the tailpipe to measure carburetor richness/leanness and he said that at all RPMs the mixture was PERFECT... Of course, this was in the morning, not in the afternoon.

I've experimented with different octane boosters and fuel treatments and none of them seem to have a dramatic affect on the pinging and temperature. I shoudl also note that at extended driving at 70 or 75 miles per hour (about 30 minutes or more of steady speed) my temperature is 230 degrees, both a 1 in the afternoon and at 1 in the morning. Is this odd to anyone else? It's a 180 degree thermostat but it's old (at least 8 years) What do you guys think?
 
G

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my temperature is 230 degrees

That sounds pretty hot.

It's a 180 degree thermostat but it's old (at least 8 years)

It's a cheap replacement, but I'm still skeptical. Engines can run hot regardless of the temp rating of the thermostat.

...although, if your temp is really that consistent than your analysis could be right on the money.

Like I said, it's a cheap replacement. Just be sure to test the new one in a pan on the stove with some other reference thermometer.
 

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at 130 pm, that is when barometric pressure and temperature is typically at it highest and humidity is the lowest, setting the coditions for pinging. The humidity doesn't rise till evening. Here's some thoughts provided that mechanically everything is ok..

1. Use a higher octane fuel
2. Richen the fuel mixture just a slight tad
3. Add Marvel mystery oil or redline to the fuel
4. add a water vapor injector (you can make one from a mayonaise jar for about $15)
 

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Discussion Starter · #14 ·
But see, it's 230 degrees even at NIGHT TIME! And it doesn't ping whatsoever, even when I touch 100 miles per hour.

I'll try Marvel Mystery, and if that doesn't work, I'll try fattening the carb up just a tad. Right now it's a "four gas vehicle" meaning that it's running incredibly clean and everything is mechanically sound in the drivetrain.

Tanks for all the suggestions! And yeah... Humidity in California is not around until about 7 or 8 in the evening, excellent point...
 

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My six banger used to do that too. If I touched the accelerator lightly it pinged badly. If I stomped on it the pinging went away. Adjusting the timing did little. I bought a rebuilt vacuum advance distributor from Pep Boys to replace the vacuum/mechanical that had been on there with little difference. Premium gas helped (92 octane). High humidity helped a lot and cool beach weather.

Eventually blew a head gasket and decided to rebuild the head (while you're at it thing). No more problem. It may have been carbon buildup. It had done it before on my previous engine but it was bored .100" over!
 
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