Make a lot of commutes with my truck. ('79 F-150, 302 4-spd) I get a lot of pinging going up a hill under load, at about 1/4 throttle. It will ping anywhere under 2,000 rpms. I have experimented with the timing, which doesn't make a difference. Have run different octane levels of fuel, and still pings. I want to say it may be carbon thats making the ping. I know carbon will hold heat, which will pre-ignite. The motor is bored over .040, which would lower compression, but the heads have been milled .010, I think. What effect would that have compared to the stock compression ratio?
Anyone have ideas or anything to add about how to stop pinging?
WrenchHead

 

Does it seem like it's only one or two cylinders, or all of them? I had a knock on one or two cylinders, so I separated the 7 and 8 cylinder spark plug wires, and that seemed to help a little bit. You can also run some SeaFoam through the intake. Pour it into the carburetor till the engine stalls. Let truck sit for 5 minutes, then re-fire it and drive for a few miles. If you get tons of smoke out the exhaust, then you probably had a carbon problem. Then when the problem comes back, run some more seafoam through it. I usually do this about every oil change.

 

Try it with your vacuum advance disconnected. I have seen a lot of vacuum canisters that had way too much advance. If that stops the ping, get a Crane adjustable unit.

 

Read my mind! I did commute with the vacuum advance off. Got rid of the ping. My throttle responce feels totally different, since it's all mechanical advance. Anyone know a cure for this problem that isn't expensive?
WrenchHead

 

Boring the motor will not lower the compression.

If you have the stock carb, you have to run the egr to make it stop pinging. Even then that may not work if you have a free-flow exhaust(headers), depending on the type of egr you have. I would:

Get the egr working with a stock carb

Put in cooler plugs

Drop down to a 180 thermostat

or

Get a non-emissions carb and

try some of the stuff above.

It will be a combination of things that finally get rid of it.

 

I did test the EGR valve, that failed. So I need to get a new EGR. Autozone has one, but I can't seem to find one out of parts catalogs. Suggestions there would be fine.
The stock carb is being run, without california emissions. My exhaust is a little free flow. Still have manifolds, but it's true dual out the side with free flow cats and mufflers. I'll have to replace the EGR, and see how that goes. It currently doesn't ping with the vacuum advance off. I also want to add that my fuel mileage is down the hole. (That points to the EGR). Motorcraft plugs are in the motor.(Stock plugs)
Any other ideas, let me know.
WrenchHead

 

A properly working vacuum advance is critical for mileage. The Crane unit is $35. It also comes with a set of springs for the mechanical advance.

 

Where can I get this crane unit at? summit...jegs? What exactly does the crane unit have/do?
Also, if anyone knows where to get an EGR valve, let me know.
WrenchHead

 

I was going to buy one a few weeks ago. The major shops were out of stock. My local speed shop could have ordered direct from Crane. There is an allen screw where the vacuum hose goes on so you can adjust the amount of advance.

I made my own by rigging up a screw inside the distributor to limit how far the linkage travels. I have a distributor machine so testing was easy.

 

I don't have access to a distributor machine, unless my local machine shop has one. How can I still test mine? Long hours with the timing light I guess, ha ha.
WrenchHead

 

I believe it comes with a good set of instructions. Crane's web site also has them I think.

 

Be careful about determining the egr is bad. This is where I messed up. And I am right in the middle of the same thing your fighting right now(pinging).

I put headers on my truck, and then started having a pinging problem. I checked everything over and when I revved the motor after it was warmed up, it looked like the egr wasn't working like it should(it wasn't opening like it used to). I took the manifold vacuum line that goes to the aircleaner and hooked it directly to the egr valve, expecting it to pull up and stall the engine. It didn't.
Ok, the egr is bad, and they want about $60.00 for a new one. Being the cheapskate I am, I took my egr to work, and carefully cut it open, expecting to find a big hole in the diaphram. It looked perfect. I made some small clamps to hold it back together, and after experimenting, I found out all the vacuum was being bled off down a mysterious hole in the middle of the diaphram. If I blocked this hole, the egr would work.

So I took and put it back on the truck with the blocked hole, and it worked. But it worked too good. When I would rev the engine, the egr would fly open and the engine would run rough. That's when I got suspicious and looked it up in the book(duh), to see what was going on.

That's when I found out that bleed hole in the middle of the diaphram has a metal plate under it. Exhaust backpressure comes up under the metal plate, and pushes it up blocking the vacuum bleed hole, making the egr work. The higher the rpms, the more backpressure, so the egr opens more. If you have this type of egr, you can look on the underside of the diaphram and see a little fuzzy filter. If you peek under it, you will see little holes where air enters when the vacuum is being bled off.

I came to the conclusion, since I put the headers on, I didn't have enough backpressure to open the valve as much as it used to. I have since went up 3 jet sizes in the carb, and put cooler sparkplugs in it. With what little egr I have, it got rid of most of the pinging. I still think I am going to a 180 degree thermostat. I checked the timing, and it is dead on the factory setting. I didn't want to retard it, or change the vaccum advance because it would affect my gas mileage and power.

 

As far as power and gas mileage is concerned, the EGR helps your over all mileage. For the timing advance, I noticed that with the vacuum advance plugged in I loose power because is to far advanced causing the ping and lose of power.(Driving down the road ofcourse). With just mechanical advance, starting off or just at idle is a little weak, but once it gets over 1500 rpms it has more power than with the vacuum but with no pings.
This brings me to my next question. Does anybody know the factory specs for vacuum and mechanical advance at a given rpm? I'm sure the factory service manuals list it, but chiltons doesn't.

Last but not least, I'm checking for vacuum leaks on my ported vacuum side. I have a vacuum diagram which is fine, but I need to know what some of the parts/abbreviations mean.
TVS
VRDV
TVV
IVV
I have the diagram picture on my computer if anyone wants to see it.
WrenchHead