67 GT Started Pinging With Load

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

So, I was driving home yesterday in my 67 GT 390 Cougar from my buddies house and I pull onto one of the county routes, I noticed a noise. So I muted the radio and there was a fairly loud pinging noise every time I dipped into the peddle. I’ve never had any issue dropping the hammer on the car and I have been using middle grade octane gas for years. So here’s what lead me to this point and what I tried. Engine is stock 390 original bore. Was rebuilt at ~80K miles. Still has standard bore and currently 99K miles.

- I got the radiator re-cored this spring but have noticed the car had been running what I felt, hotter than in the past. Never over heating though

- I started noticing that the swing away was not as responsive when I opened the door and it would only work once. It works on vacuum and usually you get about 4-5 actuations before the can runs out of vacuum.

- Last Thursday when I got home I checked out the vacuum line under the column and noticed a crack at one end. I cut it and reinstalled it and tested but it still only did one actuation. So I went hunter the hood and disconnected it and plugged the manifold port.

- Started wondering if this might be why I was running hot since a vacuum leak could cause it.

- Temp gauge on Friday seemed better but it was also hard to tell since the temp in NY had dropped some.

- So then yesterday happens. The drive to my friend’s house was great. Car was running awesome.

- After noticing the pinging sound while driving, I put it into neutral and revved it and there was no pinging. Put it back into drive and rev it and sound was back. So I figured it isn’t coming from one of the accessories on the front of the engine.

- I ruled out the thought of bad gas since I didn’t get any recently and had driven plenty of miles with what was in the tank.

- So I retarded the timing some. No change.

- Filled it full of the highest octane no ethanol gas we have in town. No change.

- Drive today in was rough at times going up a couple of big hills we have. Down shifted to get the revs up which causes the load to lessen and pinging to stop. Cruising at 65 nothing seems wrong unless you hit the throttle hard.

I should also note, cold start fires right up and idles fine. Hoping someone might have some thoughts. Hope it’s something stupid.

Thank you,

Jim

2

There is “winter “ gas and “summer” gas.

Winter gas evaporates faster. You may have gotten winter gas at the station, not your choice. Summer gas is more expensive to produce.

A hot spot in the combustion chamber is igniting the fuel before the spark plug has a chance. The 2 explosions are crashing into each other making the ping sound you hear. It can eat a hole between cylinders if left to continue. I’ve seen it.

I suspect higher ambient temps and winter gas.

Check a plug to see it’s condition.

Also, summer lead foot syndrome is starting to peak.

3

Interesting idea about the winter gas. Although I don’t drive in the winter since I’m in NY, I drive the car almost daily until the first salt hits the road and as soon as the roads are clean in the spring. I’ve had the car since 2021, and never had this issue before.

I will have to pull some plugs.

Jim

4

It could be caused by timing, excess heat or poor octane.

It’s possible your mechanical advance is sticking. Or your vacuum advance is not retracting.

Spark plugs are another possibility. Might try to go one heat range cooler.

Are you coming to Carlisle? I bring my timing light and other tuning tools.

5

I wish I was going to Carlisle. Just too much going on right now. I have a timing light, vacuum gauge and rpm meter so I will try to work on it. I will also check the distributor plates.

Thanks for the reply,

Jim

6

I checked my distributor. Vacuum plate seems to move freely. I didn’t get a chance to hook up my vacuum pump up to it though. I did have time to pull one plug. This is cylinder #5.

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The electrode looks pretty decent but there is carbon around the body. This ones got me stumped why suddenly after years of use, it would start doing this.

I do have a brand new 600 CFM carb I was planning on putting on. Maybe that, new plugs and tuning will resolve this?

Jim

7

My 351C will start pinging a bit under wide open throttle when the gas gets old. Fresh 91 octane ethanol free makes a difference,

8

I two instances I had a similar issue that turned out to be a very stiff power valve in the carb. The rubber diaphragm had turned very stiff. One more benefit of modern gas.