340 Pinging using 94

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dterry1

dterry1

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I have a 340 in my 72' Duster

I have had some pinging issues recently using 94 octane pump gas, and am going one of two ways to try and resolve the problem. I just wanted to post it on here and see what y'all think.

1. Lead substitute fuel additive/octane booster
2. Use a lower octane fuel (91,89,87)

I have tried retarding the timing to help with the early detonation, this helped a little bit. The pinging is not as severe, but it is still there.

Let me know what y'all think, your knowledge is much appreciated!
 
When and where are you getting the detonation? As in load (hill, gear) and at what RPM? What carburetor? What is your static and total timing? Could be lean, could be too much advance at the wrong time, could be engine bay heat. Any info on the 340 build wise?
 
Need to know more about the engine. Is it a original 8.5 to 1 compression or have there been mods to it.
 
How will lower octane help reduce pinging?
is vacuum advance hooked up, disconnect it and try it.
do you have 2.76 gears or a manual trans?

hi loads will ping
lean mixture will ping
advanced timing will ping
burning oil will ping
 
If it's an early 72 build, it can still have the higher compression. Forged crank, too.
 
Also, vacuum leaks can make it ping by leaning out the mixture.
 
dano said:
When and where are you getting the detonation? As in load (hill, gear) and at what RPM? What carburetor? What is your static and total timing? Could be lean, could be too much advance at the wrong time, could be engine bay heat. Any info on the 340 build wise?
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Automatic trans, all gears. It's loudest at about 2,000 rpm, altough it really only starts as the engine starts to warm up to runnning temp. (~160). Carb is a holley 650, I still have to see what the total timing and static timing are. The car is relatively new to me, it's a moderately built 340 with a street cam, bored over 0.030
 
413 said:
How will lower octane help reduce pinging?
is vacuum advance hooked up, disconnect it and try it.
do you have 2.76 gears or a manual trans?

hi loads will ping
lean mixture will ping
advanced timing will ping
burning oil will ping
Click to expand...
I tried disconnecting vacuum advance, no change that was noticeable
3.55 gears
Holds oil
 
I take it since it is new to you it's been doing this ever since you bought it?
 
RustyRatRod said:
I take it since it is new to you it's been doing this ever since you bought it?
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Actually no, that's why I think it might be the lack of fuel additive, it slowly got worse (I'm assuming as i refilled the tank, the additive got more and more diluted).
It has stopped getting worse, and it's much, much better after I retarded the distributor, although it isn't completely gone.
 
dterry1 said:
Actually no, that's why I think it might be the lack of fuel additive, it slowly got worse (I'm assuming as i refilled the tank, the additive got more and more diluted).
It has stopped getting worse, and it's much, much better after I retarded the distributor, although it isn't completely gone.
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I almost wonder if maybe you haven't gotten an advance spring that got weak and broke. I'd be looking at the distributor.
 
RustyRatRod said:
I almost wonder if maybe you haven't gotten an advance spring that got weak and broke. I'd be looking at the distributor.
Click to expand...
I considered it, but with my lack of experience I really didn't want to tinker with the distributor unless all other things have been looked at.
 
RustyRatRod said:
Absolutely it could. That's another good thought.
Click to expand...
I'll swap the plugs, add some fuel additive, and get back to y'all.

Thank you everyone for your help, everyone is very helpful like always. Really helps a new classic car owner like me, I can't appreciate y'all more.
 
dterry1 said:
I'll swap the plugs, add some fuel additive, and get back to y'all.

Thank you everyone for your help, everyone is very helpful like always. Really helps a new classic car owner like me, I can't appreciate y'all more.
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I think the fuel additive is a band aid. It sounds like the distributor is advancing too much and too soon.
 
413 said:
How will lower octane help reduce pinging?
is vacuum advance hooked up, disconnect it and try it.
do you have 2.76 gears or a manual trans?

hi loads will ping
lean mixture will ping
advanced timing will ping
burning oil will ping
Click to expand...
Tbh, I have no idea how lower octane will help reduce it

It is what my mechanic recommended
 
dterry1 said:
Tbh, I have no idea how lower octane will help reduce it

It is what my mechanic recommended
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I think he got confused. Higher octane would be what you need for different fuel, but I believe your problem is elsewhere.
 
Higher octane resists pre-ignition but will not stop it if conditions over run its ability. If you can hear it chances are its starting sooner. I would avoid additives and dig into the timing, distributor, tune and carburetor/fuel system until its sorted. Unless you got a really bad tank of gas? Did the car sit for some time i.e. old fuel?

When you say its loudest at 2k, is that at cruise in 3rd (assuming 727 or 904) or if you go WOT and it pings before it kicks down?

Do you have a vacuum gauge and timing light? Does the trans have a higher stall converter?
 
I guess I'll be that guy. 340 isn't a big block...this being the big block thread
 
dterry1 said:
I have no idea how old the spark plugs are either, would swapping those out be a possible help?
Click to expand...

I saw the plugs have been mentioned, but what brand and number are they?
To hot of plugs can cause this, as well as carbon buildup in the cylinders.
Either one of these can cause your issue.
 
Carboned up combustion chamber can cause pinging, two reasons:

- piece of hot carbon pre-ignites the mixture
- it increases the comp ratio.

Anything that cools the engine temp also reduces the chances of pinging. Too much anti freeze when it is not needed for THAT climate reduces the water's heat transfer capability.
Relying on the temp gauge can be pretty useless for pinging problems. It only tells you what the coolant temp is at the sender; the coolant might be 20* hotter around the exh valves, where there might be a hot spot.
 
I was assuming since we have a 340 that it's not driven like an 80 year old grandma only to church on Sundays, so I didn't mention carbon buildup. But yeah, if you never open the secondaries, carbon could be an issue.
 
Just to say this clearly - if the engine has stock compression - whether it's 10.5:1 (nominal) or less, it shouldn't ping on premium pump gas. Is it possible that you just got a crappy batch of gas that isn't actually 94 octane? How much gas have you run through the engine running like this?
 
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