Hi everyone, I need help on this pinging problem that I have. IT gets a little loud when going up a hill or getting down on the throttle. One thing I have noticed is that the pinging occurs when the motor is at operating temp, when its cold it seems to be alright. I checked the shop manual and this is what I have done so far.
> checked the EGR, EFE and PVC and this was fine, all where operating and the motor was pulling good vacuum
> checked the timing and it is dead on, and the timing mark is not bouncing around either
> the plug wires, cap and rotor are fairly new including the plugs

the car starts fine and idles fine except for this pinging, the mileage and carb settings are okay to. I just cannot determine why the damn thing pings, but when I start the car up and leave with out warming up, it does not ping. Once I reach operating temp then it will ping.
Is it possible that a bad plug could be the problem ? any Ideas would help. Thanks

 

How much total advance are you running, and how quick is your curve coming in? If your total is limited to 36 and your curve is slower than 3000, try richening up the carb a couple of jet sizes. You can also drop your total down to 32-34 without a major performance penalty.

 

in addition to the suggestions from Lars, try driving the car with the vacuum advance disconnected. If the ping goes away it may be vacuum advance related, we are seeing both vacuum advances that are suppling too much advance (we limit the vacuum advance to 10-12 degrees for the reformulated gas here in calif.) and vacuum advance units that are all in by 6 to 8 inches of vacuum so the vacuum advance is advancing the timing too much when the engine is under load.

good luck henry @ oles

 

You haven't provided too much info about the car Ratt....

Has this problem occured recently after some mods?
or has it occured randomly....

Do you know the compression ratio of your engine?
If it's a high comp big block rat motor then problem could be as simple as a bad batch of fuel.

What fuel (octane rating) do you usually use....

Just a simple thing to try.....as some gas stations have been known to have bad gas....
Just refill with a quality hi octane fuel and see if there is a difference.
If the tank is full, add some octane booster to elevate the fuel rating.

Driving back from Melbourne one year, I filled up at a country servo with what should have been 95 RON fuel.
Driving through the very best scenic route of Australia (Great Ocean Road) I was struggling with pinging under any load. I had to crawl up hills and coast along sedately till reaching my next fuel stop.
Refilled with good quality fuel, and no ping after that.

I now always keep a bottle of octane booster with me when touring the country regions in case I can NOT obtain premium (high octane) fuel.

PS ( we have a different scaling of our octane rating in Oz...
something to do with US uses average of ron and mon values ???)
[in Oz, 93 ron is lo octane, whilst 95 ron and above is premium.... 98 ron is available at select outlets, and is prefered in performance tunes ]

tom

 

Thanks for the advice. With reference to Ozzy Tom, I havent made any changes to the car at all. The fuel is fine, its the same that I am running in my other vehicles, although I have tryed another brand and still the same problem. As suggested by Lars and Olescarb I will try both your suggestions, I dont know why but have this feeling that the vacuum advance could be the problem. I have not made any changes to the carb settings or anything else. Other then the knocking all other aspects of the motor runs fine. The mileage, idle and starting goes with out a hitch. A buddy of mine also suggestted to check the vacuum advance, I will see what I can do. Thanks again for the tips.

 

Have you changed plugs? You may have too hot a plug.

 

Whatever your combo, don't increase the rate at which your advance comes in, vacuum or mechanical, or you'll make it worse. In any event, the vacuum advance does it's job at idle and light loads, not under heavy accelleration. Make sure this is properly connected to carb vacuum and never to manifold vacuum.

Also, not all fuels are the same, even with the same octane rating. I'm not going to name names, but there are a couple of major brands out there who take advantage of how octane ratings are averaged here in the US to pump up their numbers. Then, when the heat's on, you end up not getting what you paid for. If you've been bouncing around between different brands, find one that does the job and stick with it.

Ditto, Big2Bird: make sure your plugs are the correct heat range for your application

 

NEVER to manifold vacuum??!!
and your reasoning for this statement is......??

 

Hooking the vacuum advance directly into the manifold will not yield the intended signal to the advance as is provided by the proper take off from the carb...

 

do you understand how the vacuum advance system operates on these motors?

in MOST, (but not all) cases manifold vacuum will gain you better performance, better fuel economy, lower operating temps, and a better idle characteristic than running off ported vacuum.

Ported vacuum was used for one purpose and one purpose only and that was for lower emission control. They switched from using manifold vacuum to ported vacuum when they started adding all the emission equipment onto the cars because of federal requirements to lower HC outputs.
To that end one of the main things they did to lower HC output was to greatly retard initial timing and raise operating temps and part of the way they did that was to move the vacuum advance off of manifold vacuum to ported vacuum because by using ported vacuum you get no vacuum advance at idle which keeps the initial timing low and keeps the operating temp up. As soon as you crack open the throttle even just a small amount the ported vacuum advance now bewgins to operate the same as a manifold vacuum set-up.
The only difference between manifold vacuum and ported vacuum is at idle, above idle they operate the same.

On manifold vacuum you get full advance at idle and at low loads on the motor as as the load increases the vacuum decreases until you are under full load when there is virtually no vacuum (or very little) in the motor therefore no vacuum advance.
On ported vacuum there is no advance at idle but as soon as the throttle plates open slightly the vacuum advance will be at it's highest level than operates the same as manifold vacuum in that it decreases as the load on the motor increases.

The only real difference between the two systems is at idle.

The vast majority of people find their cars prefer operating using manifold vacuum for the best performance, lower operating temps, best fuel economy, and best idle.

I would suggest two excellent articles that deal with this issue that are well worth the reading:

http://lbfun.com/Corvette/Tech/vette...101Article.pdf

http://lbfun.com/Corvette/Tech/vette..._explained.pdf

 

You're right, but it'll run better if hooked to the manifold.

 

actually, it not right, as the vacuum advance unit gets the vacuum to increase the advance in either hook-up, the any difference is WHEN it gets it.

 

I said he was right only because that's the way GM intended it...

 

I understand... but we're talking about a pinging engine here. What might otherwise enhance performance would only serve to worsen this particular poster's problem.

edit - agree that manifold vacuum will give better performance (if tolerable without contributing to ping), as port vacuum causes timing to be retarded below optimum. Shouldn't have used the term "never".

 

On my nearly stock 76, the distributor advance is connected to the direct manifold vac port of the q-jet (lower driver side) while the ported vac is connected to the egr valve (lower passenger side) as it was FROM THE FACTORY!

Have to agree w/the group on the side of too much advance/too low octane (or the combo between them).

 

not necessarily. Pinging is detonation. Detonation happens under load but while under load the vacuum advance system is providing little or no advance.
Since the only real difference between a ported vacuum and a manifold vacuum hook-up occurs at idle (no load on the motor) the type of hook-up should will be irrelevant in this situation.

 

[QUOTE=BarryK;1559856361] Pinging is detonation. Detonation happens under load but while under load the vacuum advance system is providing little or no advance.

well yes and no, pinging/detonation can and does happen at part throttle. we have seen a lot of cars with vacuum advance induced detonation/ping problems. If the ping goes away when the vacuum advance is disconected the engine needs less advance from the vacuum advance or a vacuum advance that starts at a higher vacuum. henry @ oles

 

I will check the plugs and see what they look like as part of the diagnostics procedure. One other thing is that the pinging happens when the engine is at operating temperature, when the engine is cold I dont noticed the pinging. Is it possible that the plug in this case could be the problem ?

 

[QUOTE=olescarb;1559857557]Henery
very true, but even part throttle is creating a load on the motor compared to at idle (assuming the car is being driven and not just throttle added while sitting still). That's my point. Under load doesn't always refer to being at WOT. If it was at WOT than the vacuum advance wouldn't be relavent anyway since it wouldn't be part of the equation anymore since there would be virtually no vacuum to create the advance. Part throttle under load is typically and most common since the engine is under load but can still have enough vacuum to create the advance.

Regardless, my ORIGINAL point was simply to wonder why the statement was made that vacuum advance should never be connected to manifold vacuum - everything else has been a sidetract to that actually.

As far as the original posters pinging issue, my first recommendation would be to follow Lars advice and see where the timing is at of course and to make sure it doesn't exceed 36º with the vacuum advance disconnected and plugged and to determine at what point it's all in at. If the timing is at 36º or less and the problem isn't there with the vacuum advance still disconnected that the vacuum advance is most likely the culprit. If the problem still exists with the VA disconnected than he needs to retard the timing back.
If the pinging returns once the VA is reconnected than I'd try a different vacuum can that provides less advance.

 

[QUOTE=OzzyTom;1559849037]....problem could be as simple as a bad batch of fuel.

very first thing: check fuel quality and if you always refill in the same gas station it's maybe time to go elsewhere...

then follow all other advices, if this does not work.