Punisher66
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I'd be interested to see if I'm right. Keep us posted.
Post 200! nice....
Post 200! nice....
What's this noise I hear?
- Thread starter KMeloney
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KMeloney
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I tapped around under the truck, and am pretty sure I've ruled out the heat shield. I guess it COULD be knocking, since I'm using 87 octane as well. (Incidentally, with my '02 Tahoe, I had some tapping at start up. I asked a GM tech about it, and he immediately asked me what octane gas I was using. When I said 89, he said, "Why? You should be using 87." Kind of took me back, assuming he'd say that I should be using a HIGHER octane. He said the engine was designed to run on 87. So, who knows!)
How about this: Can someone describe exactly what "pinging" or "knocking" sounds like? When I had a supercharged Mustang, I was told that it sounded like "BBs in a can." But that was apparently from HIGH rpms with a too-lean condition. Could I be experiencing this at LOW rpms, under load? That's when I hear it.
Thanks!
How about this: Can someone describe exactly what "pinging" or "knocking" sounds like? When I had a supercharged Mustang, I was told that it sounded like "BBs in a can." But that was apparently from HIGH rpms with a too-lean condition. Could I be experiencing this at LOW rpms, under load? That's when I hear it.
Thanks!
GreenDen07
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"I use 87 octane" -- gents, sounds exactly like pinging/knocking/detonation...the "not-so high-pitched metal sound", esp if it fades away when letting up on the pedal.
Short answer:
To see if the sound is from detonation, use the highest octane for awhile.
If the sounds go away, you've found the cause.
Longer answer:
If you don't know the fool-proof drill, first use as much of the current fuel down to 1 or 2 gallons (we like to do that anyway, right?), then put in the highest octane in your area (some are 91 like here in GA, some 93, like I found in eastern OK last summer). It really shouldn't matter how much fuel you use, because the percentage of 87 will stay the same. Just do the hill test. If you really had pinging, and due to using 87, then you'll hear less pinging. If you still hear some, then run that all down to just a gallon or 2, and then fill up with 91/93 again, test again, and there should be even less pinging. If so, then run down to 1 or 2 gal's again, and this time use 89 (or whatever your middle grade is). Same test - you may get lucky and the pinging is still less or gone.
The GM tech would be correct if indeed the engine were designed for 87, but perhaps it's not a high-quality 87. If an engine is pinging at an octane higher than it's designed for, it could be poor gas, or an aging engine, old plugs, wires, timing, etc. If an engine pings with 89, it'll do so at any lower octane.
If you've never experienced hearing an engine pinging and then, using higher octane, and then noticing it's gone, it's a sweet feeling. The chemistry is real. Knocking/detonation occurs when an area of fuel/air in the cylinder ignites outside the flame front, or blast area, so to speak. It ignites separate from the spark plug area because there's just some residual heat laying around above the piston. The spark causes the main explosion, and that flame area expands. If some fuel outside that area happens to ignite, you're hearing that secondary explosion, which of course rattles off the metal cylinder..it's not the sound of two metal pieces hitting each other - it's the sound wave bouncing of the wall, which is why the sound is often described as dull. Fortunately, this all happens after the piston reaches the top and is on its way down. Unfortunately, it's not good for the engine. It's not going to crack a cylinder the first few times, but eventually it'll take its toll.
Using any higher octane makes it harder for these extra renegade explosions to happen, because the fuel ignites at a higher temperature, and these hotter areas aren't hot enough to explode on their own, and therefore the only source of ignition is the plug, which is always guaranteed to be hot enough to ignite the fuel.
This is akin to pre-ignition, but that's when fuel ignites "before" the spark plug fires, because of some hot pieces of carbon still wandering around, or some hot spot on the wall, or a plug that stayed just a little too hot for too long, or not using the right plugs temperature-wise. Pre-ignition is worse, because the explosion happens while still on the upstroke, putting stress on all sorts of parts.
This test will cost a little $$ and time, but will settle the question.
- Dave H.
Short answer:
To see if the sound is from detonation, use the highest octane for awhile.
If the sounds go away, you've found the cause.
Longer answer:
If you don't know the fool-proof drill, first use as much of the current fuel down to 1 or 2 gallons (we like to do that anyway, right?), then put in the highest octane in your area (some are 91 like here in GA, some 93, like I found in eastern OK last summer). It really shouldn't matter how much fuel you use, because the percentage of 87 will stay the same. Just do the hill test. If you really had pinging, and due to using 87, then you'll hear less pinging. If you still hear some, then run that all down to just a gallon or 2, and then fill up with 91/93 again, test again, and there should be even less pinging. If so, then run down to 1 or 2 gal's again, and this time use 89 (or whatever your middle grade is). Same test - you may get lucky and the pinging is still less or gone.
The GM tech would be correct if indeed the engine were designed for 87, but perhaps it's not a high-quality 87. If an engine is pinging at an octane higher than it's designed for, it could be poor gas, or an aging engine, old plugs, wires, timing, etc. If an engine pings with 89, it'll do so at any lower octane.
If you've never experienced hearing an engine pinging and then, using higher octane, and then noticing it's gone, it's a sweet feeling. The chemistry is real. Knocking/detonation occurs when an area of fuel/air in the cylinder ignites outside the flame front, or blast area, so to speak. It ignites separate from the spark plug area because there's just some residual heat laying around above the piston. The spark causes the main explosion, and that flame area expands. If some fuel outside that area happens to ignite, you're hearing that secondary explosion, which of course rattles off the metal cylinder..it's not the sound of two metal pieces hitting each other - it's the sound wave bouncing of the wall, which is why the sound is often described as dull. Fortunately, this all happens after the piston reaches the top and is on its way down. Unfortunately, it's not good for the engine. It's not going to crack a cylinder the first few times, but eventually it'll take its toll.
Using any higher octane makes it harder for these extra renegade explosions to happen, because the fuel ignites at a higher temperature, and these hotter areas aren't hot enough to explode on their own, and therefore the only source of ignition is the plug, which is always guaranteed to be hot enough to ignite the fuel.
This is akin to pre-ignition, but that's when fuel ignites "before" the spark plug fires, because of some hot pieces of carbon still wandering around, or some hot spot on the wall, or a plug that stayed just a little too hot for too long, or not using the right plugs temperature-wise. Pre-ignition is worse, because the explosion happens while still on the upstroke, putting stress on all sorts of parts.
This test will cost a little $$ and time, but will settle the question.
- Dave H.
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Wow Dave....very in depth post 
I'd already decided to step up my octane at next fill up(probably by the end of the week) but this is great info to have 
would it work just as well (and maybe even be cheaper) to still fill up with 87 octane but toss in some octane booster??
I'd already decided to step up my octane at next fill up(probably by the end of the week) but this is great info to have would it work just as well (and maybe even be cheaper) to still fill up with 87 octane but toss in some octane booster??
02Lightning
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It sound like pre ignition to me but don't these car have spark knock sensors to retard the timing for this?
GreenDen07
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Octane Boosters - can't vouch for them. Here are a couple of links. Evidently they're geared somewhat towards people who race.
http://ezinearticles.com/?Octane-Boosters-and-the-Truth-Behind-Them&id=802568
"Despite the benefit, use boosters sparingly as most rely on MMT as a means of boosting the octane. Excessive MMT can cause problems with sensors, injectors, or even the exhaust."
{Yes, they misspelled "boosters" in the following url}
http://volvospeed.com/Review/misc_performance_volvo_reviews/octane_bosters_general.html
The following pdf recommends against using boosters that use MMT:
http://www.chevrolet.com/assets/pdf/owners/manuals/2011/2011_chevrolet_malibu_owners.pdf
*****************************************************************************
O2Lightning: you're absolutely right. But from that "ezinearticles.com" article, "[octane]... is a rating [which] means to measure a fuels resistance to pre-ignition", at one point it says a low octane leads to detonation, but in another paragraph says it can lead to pre-ignition, so I'm still deciphering their explanation:
"Let's first assume you have a car that runs well on 91 octane. ... By going down to 87 octane you will achieve better mileage, but could risk detonation depending on your cars engine."
"In modern vehicles with knock sensors the timing is constantly varied to achieve the best balance between performance and economy....The other end of the spectrum is less octane. The down side here is the risk or [think they meant to say "of"] pre-ignition and high EGTS. Both of these can lead to melted or bend pistons. Valves and the head is also placed in risk. If you have a modern vehicle it will detect this and retard timing to prevent damage."
****************************************************************************************
BTW, as far as engines that miss, our '95 Mercury Villager (same as Nissan Quest then) was missing more and more, and it turned out to be spark plug wires. But using Techron additive (which was not an octane booster) definitely made it miss less...then with new plugs it was better, then new wires -- didn't miss at all.
http://ezinearticles.com/?Octane-Boosters-and-the-Truth-Behind-Them&id=802568
"Despite the benefit, use boosters sparingly as most rely on MMT as a means of boosting the octane. Excessive MMT can cause problems with sensors, injectors, or even the exhaust."
{Yes, they misspelled "boosters" in the following url}
http://volvospeed.com/Review/misc_performance_volvo_reviews/octane_bosters_general.html
The following pdf recommends against using boosters that use MMT:
http://www.chevrolet.com/assets/pdf/owners/manuals/2011/2011_chevrolet_malibu_owners.pdf
*****************************************************************************
O2Lightning: you're absolutely right. But from that "ezinearticles.com" article, "[octane]... is a rating [which] means to measure a fuels resistance to pre-ignition", at one point it says a low octane leads to detonation, but in another paragraph says it can lead to pre-ignition, so I'm still deciphering their explanation:
"Let's first assume you have a car that runs well on 91 octane. ... By going down to 87 octane you will achieve better mileage, but could risk detonation depending on your cars engine."
"In modern vehicles with knock sensors the timing is constantly varied to achieve the best balance between performance and economy....The other end of the spectrum is less octane. The down side here is the risk or [think they meant to say "of"] pre-ignition and high EGTS. Both of these can lead to melted or bend pistons. Valves and the head is also placed in risk. If you have a modern vehicle it will detect this and retard timing to prevent damage."
****************************************************************************************
BTW, as far as engines that miss, our '95 Mercury Villager (same as Nissan Quest then) was missing more and more, and it turned out to be spark plug wires. But using Techron additive (which was not an octane booster) definitely made it miss less...then with new plugs it was better, then new wires -- didn't miss at all.
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Do these engines have history of pinging? It seems like a strech to me (with very little small block Chevy experience) that a push rod truck engine would have pinging issues when it is designed for 87 octane. Did they bump compression up above 10:1 on the 5.3L?
Obviously it can't hurt to run higher octane for awhile and see if it goes away but I would be surprised. Running 87 is one of the reasons I went with the Tahoe over the Grand Cherokee with the HEMI (357hp version). That HEMI is an awesome motor in the smallish GC, but it needs 89 octane and gets the same mileage as the much larger Tahoe...plus it has 16 spark plugs!
Obviously it can't hurt to run higher octane for awhile and see if it goes away but I would be surprised. Running 87 is one of the reasons I went with the Tahoe over the Grand Cherokee with the HEMI (357hp version). That HEMI is an awesome motor in the smallish GC, but it needs 89 octane and gets the same mileage as the much larger Tahoe...plus it has 16 spark plugs!
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