Hey guys
I've been trying to resolve a pinging problem for months now. I had a friend at work tell me that running a higher octane would help with pinging. I know it is supposed to help but obviously in my case it didn't because theres some other problem that I probably won't figure out for a while because I'm too stubborn and cheap to go to a mechanic. Anyways, he said 87 octane wasn't even available when my truck was built in 1981 and I should be running 93. I'm just wondering what octane you guys run in your trucks and whether you know some history about octane availability.

 

I run 87 in mine with no problems. And I have had several of these trucks, with both M's and W's, and have run 87 without any issues at all.

As for octane, I don't remember when we went from Ethyl and Regular terminology to octane ratings. But I doubt that all we had in the 80's was the equivalent to 93 as I'm fairly sure that by then we'd changed to octane #'s. However, I think it started about '73 as the in-leaded fuels were introduced. But, initially there were two numbers - research and engine. So it was confusing.

 

The Terrible Blob,

How many miles on your engine and what kind of shape is it in? Years ago, I worked in a laboratory of a large oil company. This company used the terminology of "octane creep", which described the needs of an engine as it aged and a buildup of carbon in the combustion chamber effectively increased the compression, requiring a higher rated octane fuel.

As Gary Lewis pointed out, many of us use 87 octane with no problem, as long as the timing is correct. These engines [stock] are low compression [~8.4 to 1] and should not need higher octane fuels.

Have you checked your timing? Is the pinging occuring under slight load? Is your vacuum hose connected to the cannister of the distributor and is this feature working? When under a load, the vacuum cannister should retard [actually remove the vacuum induced ignition advance] the timing when under a load, preventing pinging [preignition].

Have you tuned the truck recently?

 

Has your EGR system been disabled or removed?

 

Here is what my 1981 Ford Owner's Manual says:

Octane Rating

Federal regulations require that each retail gasoline dispensing pump must display on its face a black bordered yellow label bearing the Minimum Octane Rating in black letters. This displayed Octane Rating will be the average of the Research and Motor Octane Numbers and will appear on the pump label as an (R+M)/2 number.

Your vehicle, when properly maintained and used, has been designed to operate using gasoline with an (R+M)/2 Minimum Octane Rating of 87. Use of gasoline with octane ratings lower than 87 can cause persistent, heavy engine spark knock, which can lead to engine damage. If your engine knocks heavily when you use gasoline that meets the octane rating recommendations of this manual, or if you hear continuous spark knock while maintaining cruising speed on level roads, take your vehicle to your dealer for correction of the problem. However, you may notice occasional, light engine spark knock of short duration when either accelerating or driving up hills. This should not cause concern because maximum fuel economy benefit from the gasoline's octane rating is obtained under conditions of occasional, light spark knock. Buying a gasoline with an octane rating higher than that which allows occasional spark knock will not damage your vehicle, but it is not necessary for the proper operation of your vehicle.

Octane rating and unleaded gasoline availability may vary between gasoline stations. If you plan to drive your vehicle outside the United States, check the availability of gasoline of the correct type and rating in the area you expect to visit.

 

Thanks for the owners manual exerpt, very informative. This occasional light knock part sounds familiar but my pinging engine worries me a bit. I've recently tuned the ignition timing and carb, the engine seems much more comfortable with a higher idle around nine hundred instead of six hundred because when its lower it shakes like its about to stall out. I don't know if I'm wrong on that.
I still have to check my EGR system and the vacuum timing advance. Many of my vacuum lines are also old and dry. I've been trying to figure out how to replace these because so many of them have weird fittings and they divide into two lines or go from a larger hose to a smaller one.. It looks like i'm going to need a whole set of vacuum lines and connectors.

 

I'd throw some 91 octane fuel in it just to see if it makes any difference.

 

You should be able to replace those vacuum lines with vacuum hose from the auto parts store. Just remove them one at a time and label them with masking tape (i.e. brake booster, cruise control, EGR, etc.). Also make sure you take plenty of pictures before disassembling the vacuum hoses. And post a few so we can see.

DOH!

 

Heads up, you know this thread started and ended back in 2014...

 

87 was not available and 93 may help. But i would start by retarding your timing back 2 degrees, and see what happens then. There are a variety of potential cures but we will need more details to give much more advice than this. Ie Engine? Compression ratio? Operating temp/ t stat temp?, stock or improved? Upgrades? An such? Erg, dead thread!

 

I did see this but for the OP and people running the great 300 six I will post for them what I have found.
You are right on needing to know a little more of what the OP has but his sig says 300 six.

I have found the 300 is a whole different animal when it comes to pinging, and yes I also have pinging.
I do not have a working EGR and that seams to be a big thing for pinging on the 300 motors from what I have seen posted.
I have also changed the springs for the weights, yes you need to pull the distributor and take it apart to get to them, and I have also adjusted the vacuum advance can. BTW this only changes at what HG the vacuum starts to act on advancing not how much it will add.

I do have my base timing set to something like 12* to 14* BTDC. If I retard it, it takes longer (more cranking) to fire up. I dont remember what total is with mechanical & vacuum with out digging out my notes.
I mostly get pinging when I pull the car clubs 20' enclosed trailer and if I back out of the throttle a little it will stop till back under load so I am thinking it is vacuum advance adding too much?
Running high test does help cut the pinging way down so when I know I will pull the trailer I will get high test fuel.

If a motor is in poor shape, burning oil, that can lead to pinging, mine does not burn / use oil, and I cant see it having carbon build up as it is driven on the high way at a good speed (70+ mph) for at least 10+ miles when I can.
If anyone thinks they have carbon build up you can try this trick.
Get motor up to temp, get a large pop bottle filled with cold water. Raise the RPM and pour the water down the carb but not too much to kill the motor.
This cold water hitting the hot carbon breaks it up and gets blown out the tail pipe.
I also dont think carbon is a problem with todays fuel like it was way back in the day but have ot pulled apart a motor that has run todays fuel its whole life.

Also the factory uses ported vacuum for vacuum advance. You might try manifold vacuum to see how that works for you. I have not tried this on my truck but may some day?
I dont know of a easy way to limit the advance, vacuum or machinal as I have not really looked but that could be a option to stop pinging.

But you really need to see what you timing & both advances are doing and write it down so you can see what is going on and then have a game plan.
Dave ----