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pinging when floored? only 10 degrees advanced

SAC69

SAC69

Active Member
Donator
I don't hit the throttle that much but have recently caught the engine pinging noticeably under 3/4 + above throttle, rpm does not matter. I checked the timing last night and it's only set at 10 degrees advanced, factory setting is 6. It's not as if the engine is too hot, it's a factory sweep gauge only so I really can't tell exact temp but it's in the middle or less. It's a 351W still stock internally, originally 9.5 compression, but I have a Duraspark distributor, Summit ignition box, headers, alum intake, Summit carb, Ford wires. (I've had this distributor for 8 yrs or so but bought it used, not sure of the advanced curve setting.) Supreme fuel here in Calif is 91 octane which I always use . Do I simply need octane booster or is something amiss?

Thanks for any info.
 
Vacuum advance acting screwy, perhaps? Did you fuel with diesel by any chance?
 
No chance of filling with diesel in error. How to tell if vacuum advance is a prob? How do you tell what the full advance is anyway? I know it's supposed to be "all in" 2500 or so (?) but how to verify?
 
Remove vacuum line and plug it, then measure mechanical advance with timing light while increasing curb idle speed. Measure RPM with tach.
Then install vacuum line and repeat measurements.
 
You don't need octane boost and it is a scam anyway. Read the fine print and scientific testing on the stuff. The "good" ones only get you a tenth of a point or so.

If all the diagnostic testing doesn't reveal a cause there is the chance you simply got a "bad" tank of gas at your last fill up. It happens.
 
At large throttle openings, vacuum should be low so I wouldn't expect the vacuum advance to be an issue. However, you can disconnect and plug the line and road test without the vacuum advance to see if it makes a difference. If so, see if your advance diaphragm is adjustable (through the vacuum opening with an allen wrench) and turn it a couple turns CCW and try again. Repeat as needed.

My guess is that the problem IS ignition timing related due to too much cylinder pressure for the octane available. I'd drop your initial timing back to 6* and look toward expanding your mechanical advance to compensate.
 
Octane booster also coats the combustion chamber, which in turn eventually raises your octane requirement. Learned that little known detail while I was at JBA in the late 80's.
AFA a weird cause of "pinging," I chased one for quite awhile about 15 years ago. Turned out to be a weak bendix situation in the old factory FoMoCo starter-
under moderate to heavy acceleration the starter was getting pulled toward the flexplate teeth. Guess what that sounded just like?
Took me forever and a lot of hair pulling before I figured out that the cause of the pinging had nothing to do with octane, timing, etc.
 
Either run some 93 or 100 octane, don't need much. Try that after backing off the timing and you'll know that to run more advance, you just have to fork out more $$ for fuel!
 
You've never clarified how long this issue has been occurring. If all was good for so long an now all of a sudden it has started don't over think the problem. Rule out the fuel being the cause first. Then check that the timing hasn't changed somehow.
 
Thanks for the tips guys, I'll check the timing & advance a bit more. It's a recent problem that started beginning of summer. I can't find octane over 91 without driving a hour to Infinion raceway. I refueled last night at the local mom+pop station, will see if that helps or maybe gassing at the Chevron will result in better quality gas but I thought it's all about the same.
 
Check your spark plug wires, coil wires, and spark plugs. You might have a bad spark plugs that is foul. Check wires that might be loose. Simple stuff first.
 
SAC69 said:
Thanks for the tips guys, I'll check the timing & advance a bit more. It's a recent problem that started beginning of summer. I can't find octane over 91 without driving a hour to Infinion raceway. I refueled last night at the local mom+pop station, will see if that helps or maybe gassing at the Chevron will result in better quality gas but I thought it's all about the same.
Click to expand...
Just because I cant get past the gas component...

Doesn't Cali do seasonal blend gasoline? I wonder if something about the summer blend fuel could be to blame. Also, not all gas is equal by a long shot. Yes, it is all supposed to be regulated and tested etc. but I can't tell you the number of times over the years I have had to get gas a an out of the way non-big brand station only to have the same type of issues you describe.
 
Horseplay said:
Just because I cant get past the gas component...

Doesn't Cali do seasonal blend gasoline? I wonder if something about the summer blend fuel could be to blame. Also, not all gas is equal by a long shot. Yes, it is all supposed to be regulated and tested etc. but I can't tell you the number of times over the years I have had to get gas a an out of the way non-big brand station only to have the same type of issues you describe.
Click to expand...


Yes....we continue to be special out here in California. Around Memorial Day they phase in the summer blend, gas prices spike, and we have cleaner air. Of course then around Labor Day they go back to winter blend, again prices go up due the change over......a vicious circle at best.
 
Pull out some of your spark plugs... are they bone white with small dark marks? You may have developed a lean condition...
 
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