Engine Ping/Tick/Knock 5.3L V8

PistolPete · March 30, 2005

Dear GM-Tech,

I own a 2003 Chevy Silverado Z71 w/5.3L V8 and Automatic Trans (15k+ miles). Recently I have noticed some engine pings or ticks under certain conditions. The conditions are....

When the truck is warm (at or near normal temp) and I am going up a hill or incline with the gas partially or halfway pressed down.

If I give the truck a good amount of gas/acceleration on a hill the noise goes away. The noise also does not happen if I am using 92-octane gas. I spoke with a "general" auto tech I know here in town and he thought it might be the knock sensor not properly functioning. He said that if I took my truck to a GM service shop the malfunctioning knock sensor would not show up as an error code. From searches on the net it appears that the 2003 5.3L V8 actually has two knock sensors. Do you think it truly is a malfunction knock sensor(s) or something else? Any help would be much appreciated.

Sincerely,

Pete Felten

[email protected]

PistolPete · April 5, 2005

Yes, there are two knock sensor under the intake. We've had some problems with the wells the knock sensors sit in filling with water (do you wash your engine?) and causing corrosion of the connector.

Keep in mind that knock sensor don't forsee detonation occuring and stop it before it happens. It has to occur before they will put out a knock signal to the PCM, so you may hear some. A little bit of knock may not even cause the PCM to react. Under certain conditions, such as you describe, a little bit of detonation is not abnormal. As long as it is not continuous or heavy, it's not a problem.

<{POST_SNAPBACK}>

Thanks GM-Tech,

Before I saw your message, I took a look in my owner’s manual. On page 5-5 of the manual it says the following...

"....A little pinging noise when you accelerate or drive uphill is considered normal. This does not indicate a problem exists or that a higher-octane fuel is necessary."

I guess the issue I have is normal, but it's irritating. I used to have a 1999 Dodge Ram 1500 that started lightly pinging and eventually got louder and louder until I got a serious engine intake manifold problem. Ever since then, I am a little nervous when I hear abnormal sounds come from the engine.

I do notice a little bit of a miss from time to time though. When my truck is just idling I get some shakes from the engine. I wonder if replacing the knock sensors wouldn’t be a bad idea just for the heck of it.

Pete

ness5575 · April 7, 2005

Dear GM-Tech,

I own a 2003 Chevy Silverado Z71 w/5.3L V8 and Automatic Trans (15k+ miles). Recently I have noticed some engine pings or ticks under certain conditions. The conditions are....

When the truck is warm (at or near normal temp) and I am going up a hill or incline with the gas partially or halfway pressed down.

If I give the truck a good amount of gas/acceleration on a hill the noise goes away. The noise also does not happen if I am using 92-octane gas. I spoke with a "general" auto tech I know here in town and he thought it might be the knock sensor not properly functioning. He said that if I took my truck to a GM service shop the malfunctioning knock sensor would not show up as an error code. From searches on the net it appears that the 2003 5.3L V8 actually has two knock sensors. Do you think it truly is a malfunction knock sensor(s) or something else? Any help would be much appreciated.

Sincerely,

Pete Felten

[email protected]

<{POST_SNAPBACK}>

Pete - I have noticed that certain gas stations cause my truck to ping under situations very similar to what you are describing. I dont know if its additives that they do/dont add that do it or??? but as soon as i switched gas stations it went away....

GM-Tech · April 6, 2005

Don't get your shorts in a bunch, that was a serious question.

Why don't I know this as a GM tech? Well, I guess because I've driven many a vehicle while monitoring degrees of retard being requested and knock counts and I've never seen this constant state of retard you say they all have. Since I live in S. Florida, I'd say we have pretty hot weather most of the time, sometimes even in the winter.

Yes, I will admit I'm not an expert in engine theory, design and engineering. I have real world experience. Do I know everything about fixing one of these beasts? Absolutely not, but I think I do pretty good and I'm above average.

If you'd like to take over as the "expert" here, have at it!

snoman · April 5, 2005

Keep in mind that knock sensor don't forsee detonation occuring and stop it before it happens. It has to occur before they will put out a knock signal to the PCM, so you may hear some.

Actually in theory it listens for vibrations in the block that spark knock causes and traps it before it is heard except in extreme cases where it cannot retard it enough and it has a fast attack to retard spark and then it slowly restores it while listening (feeling) for knock again. If all goes well you never will hear it though you see it in performance and MPG. My 2000 5.7 Vortec has never pinged once on any fuel I have run but it is a lot more sluggish with 87 than 91 because spark control is lees active (if active at all) with 91 octane.

GM-Tech · March 30, 2005

Yes, there are two knock sensor under the intake. We've had some problems with the wells the knock sensors sit in filling with water (do you wash your engine?) and causing corrosion of the connector.

Keep in mind that knock sensor don't forsee detonation occuring and stop it before it happens. It has to occur before they will put out a knock signal to the PCM, so you may hear some. A little bit of knock may not even cause the PCM to react. Under certain conditions, such as you describe, a little bit of detonation is not abnormal. As long as it is not continuous or heavy, it's not a problem.

fastdrvr23 · April 7, 2005

Dear GM-Tech,

I own a 2003 Chevy Silverado Z71 w/5.3L V8 and Automatic Trans (15k+ miles). Recently I have noticed some engine pings or ticks under certain conditions. The conditions are....

When the truck is warm (at or near normal temp) and I am going up a hill or incline with the gas partially or halfway pressed down.

If I give the truck a good amount of gas/acceleration on a hill the noise goes away. The noise also does not happen if I am using 92-octane gas. I spoke with a "general" auto tech I know here in town and he thought it might be the knock sensor not properly functioning. He said that if I took my truck to a GM service shop the malfunctioning knock sensor would not show up as an error code. From searches on the net it appears that the 2003 5.3L V8 actually has two knock sensors. Do you think it truly is a malfunction knock sensor(s) or something else? Any help would be much appreciated.

Sincerely,

Pete Felten

[email protected]

<{POST_SNAPBACK}>

Pete - I have noticed that certain gas stations cause my truck to ping under situations very similar to what you are describing. I dont know if its additives that they do/dont add that do it or??? but as soon as i switched gas stations it went away....

<{POST_SNAPBACK}>

Same with me guys. My old 89' with a 305ci would ping alot unless I used either Texaco, Shell, or Amoco (our main brand names here). It made no sense, but it would sure stay quiet that way. I checked the valvetrain out really well when I replaced the valve stems, and they looked fine. It was pretty weird to me.

On the same note, I've run all sorts of gas through my 03', and never had a bit of pinging, even with the 3.42 rear end on really long hills between here and N.E. Tenn... I'm glad too.

Good luck man!

GM-Tech · April 5, 2005

Actually in theory it listens for vibrations in the block that spark knock causes and traps it before it is heard

There's nothing magical about a knock sensor. It just has a piezoelectric component that generates a voltage when exposed to pressure or vibration. Yes, I can see where it may pick up a detonation event that is not quite intense enough or of long enough duration that we would pick it up with our ears, However, it still can't see into the future. Must be that ol' "space time continuum sensor" at work again.

Bottom line... I hear detonation in a wide variety of our vehicles, knock sensor notwithstanding. Detonation doesn't always occur at a small level and increase in intesity over time. Many times, the conditions are just right for detonation to occur and the sensor cannot forsee that happening.

snoman · April 7, 2005

Don't get your shorts in a bunch, that was a serious question.

Why don't I know this as a GM tech? Well, I guess because I've driven many a vehicle while monitoring degrees of retard being requested and knock counts and I've never seen this constant state of retard you say they all have. Since I live in S. Florida, I'd say we have pretty hot weather most of the time, sometimes even in the winter.

Yes, I will admit I'm not an expert in engine theory, design and engineering. I have real world experience. Do I know everything about fixing one of these beasts? Absolutely not, but I think I do pretty good and I'm above average.

If you'd like to take over as the "expert" here, have at it!

<{POST_SNAPBACK}>

I am not trying to displace you, only augement as my understand of IC engine theory is quite good. You seem to be in more of a twist over this than me. When you drive and monitor you will not see much retard ativity when cruising with low octane fuel but you will under heavy engine loads and around toewn under load and where it will have the greatest impact on MPG and performance. I gained about 1 MPG in overall averages with my 2000 K3500 by using 89 or higher octane and it is perkier too that when I use 87 in it. Even my wifes 2000 cherokee with a 2.5 GM engine runs smoother with 89 or higher in it to as you can feel it in the engine as speed. Given todays fuel prices and that plus is only 3 to 4% more generally it is kinda foolish not to use it it over 87 octane and possible gain 5 to 10% more MPG and better responce too. It may actually be cheaper to run your SUV on better gas these days and in the days to come.

GM-Tech · April 7, 2005

When you drive and monitor you will not see much retard ativity when cruising with low octane fuel but you will under heavy engine loads and around toewn under load ...

Yeah, I guess I am in a twist over this.

Have you actually worked in the field on these things? How many of these vehicles have you driven with a Tech 2 (or similar device) while monitoring retard and knock counts? If you've done a considerable amount of work like that, that would impress me. Not some college degree or papers written on thermodynamic principles.

I can say that I have driven plenty. Probably hundreds over the years. It isn't that "you will not see much retard ativity when cruising" --I see NONE. Even on accel, none. The only time I see knock counts or retard is when I hear it. That's my real world experience, not theory.

I'm off this week, but I guess when I get back I'm going to have to find some time to go out and do some data captures on one of these vehicles and post an image of an acceleration curve with knock and retard data plotted right along side of it to show some real world experiences.

snoman · April 6, 2005

Actually in theory it listens for vibrations in the block that spark knock causes and traps it before it is heard

There's nothing magical about a knock sensor. It just has a piezoelectric component that generates a voltage when exposed to pressure or vibration. Yes, I can see where it may pick up a detonation event that is not quite intense enough or of long enough duration that we would pick it up with our ears, However, it still can't see into the future. Must be that ol' "space time continuum sensor" at work again.

Bottom line... I hear detonation in a wide variety of our vehicles, knock sensor notwithstanding. Detonation doesn't always occur at a small level and increase in intesity over time. Many times, the conditions are just right for detonation to occur and the sensor cannot forsee that happening.

<{POST_SNAPBACK}>

But given the times per seond that it does sample for vibration, as long as it is working properly it will prevent the knock from being audibly heard by the end user of vehical. The only reason you would here knock is when the system cannot retard spark enough to prevent it. Realistically with the 9 to 1 plus ratio used in modern gas engines it is mostly in a constant state of retard when 87 octane fuel is used, especailly in hot weather. Also, the ECM does have a learning mode and can remember certain combinations of throttle and rpm and use proper spark and fuel setting for it and so it can somewhat forsee the future as it can constantly change its baseline to work from as conditions vary. I remember when GM first brought out ESC (Electronic Spark Control) with the 305 being first to have it about 25 years ago. Back then it had a 20 degree working range and I am not sure what its current limitation are in todays designs.

GM-Tech · April 6, 2005

Realistically with the 9 to 1 plus ratio used in modern gas engines it is mostly in a constant state of retard when 87 octane fuel is used, especailly in hot weather.

Where do you get this stuff?

snoman · April 7, 2005

When you drive and monitor you will not see much retard ativity when cruising with low octane fuel but you will under heavy engine loads and around toewn under load ...

Yeah, I guess I am in a twist over this.

Have you actually worked in the field on these things? How many of these vehicles have you driven with a Tech 2 (or similar device) while monitoring retard and knock counts? If you've done a considerable amount of work like that, that would impress me. Not some college degree or papers written on thermodynamic principles.

No need to be in a twist over it as it is not worth it. Yes I have experamented a lot in the past with engine and monitored fuctions with scanner and laptops (add I am considering getting back into the laptop software thing too) so I know what is going on under the hood. GM (and others) also use EGR to retard ping and control the production of NOx by lowering peak combustion temps along with timing. Also bear in mind that some of your data is squewed best GM reatds the base line curve to begin with because they know people are going to run 97 in them and the ECM remember these average parameters too and averages lower spark timings based on them so you may not see a active retard but overall it is because you simple cannot run 9.5 CR in a big engine on 87 without playing with timing and EGR to prevent knock. Also, bear in mine that it was "college boys" with sheep skins that designed the engine you test and the equipment that you use to test it.

snoman · April 8, 2005

Dear GM-Tech,

I own a 2003 Chevy Silverado Z71 w/5.3L V8 and Automatic Trans (15k+ miles). Recently I have noticed some engine pings or ticks under certain conditions. The conditions are....

When the truck is warm (at or near normal temp) and I am going up a hill or incline with the gas partially or halfway pressed down.

If I give the truck a good amount of gas/acceleration on a hill the noise goes away. The noise also does not happen if I am using 92-octane gas. I spoke with a "general" auto tech I know here in town and he thought it might be the knock sensor not properly functioning. He said that if I took my truck to a GM service shop the malfunctioning knock sensor would not show up as an error code. From searches on the net it appears that the 2003 5.3L V8 actually has two knock sensors. Do you think it truly is a malfunction knock sensor(s) or something else? Any help would be much appreciated.

Sincerely,

Pete Felten

[email protected]

<{POST_SNAPBACK}>

Pete - I have noticed that certain gas stations cause my truck to ping under situations very similar to what you are describing. I dont know if its additives that they do/dont add that do it or??? but as soon as i switched gas stations it went away....

<{POST_SNAPBACK}>

Not all gas is created equal and some stations have been know the mix their gas to boost profits even though it is not legal when not marked. I have had consistant results with Shell and Citgo here anyway. Gaswith alchol in it is more knock resistant not only because alchol tnends to raise octane a bit but it also tends to slow the speed of combution a fraction too which help detonation as well. Also higher octane fuel not only retard dentenation it also burn a bit slower too and tends to lower peak combustion temps a bit too vs regular. Ideally, you want to use the minimum octane your engine will burn without knocking while without having to retard spark to do it as when you reach that point, you will gain nothing with a higher octane fuel. GM should put a idiot light on the dash board to rell people when it is detecting knock and that they are not gettin maximum possible performace from fuel being used. This would meet with resistance for sure but in the long run it might lead to better quality motor fuel as people would tend to buy the brands of gas that "knocked" less. It would be very easy to add too.

snoman · April 6, 2005

Realistically with the 9 to 1 plus ratio used in modern gas engines it is mostly in a constant state of retard when 87 octane fuel is used, especailly in hot weather.

Where do you get this stuff?

<{POST_SNAPBACK}>

I do not "get it" anywhere as I know it first hand from lifes experiances and I even wrote a thesis on thermodynamic principles on a internal combustion engine in college many years ago (and for which I received a excellant grade too). The question one might ask is why do you not know this yourself as a GM Tech as it is common knowledge in engine theory, design and in engineering circles. They main reason that they use spark control is to bandaid fix the octane requirement so the consumer can use 87 but then later complain about MPG. (when they took the lead out of fuel for catlysts and lead emmissions the octane of regular dropped) If you run much over 8.5 to one you better use good gas or good spark control with 87 octane in a larger displacement engine under load (the smaller the engine the more tolerant it is). While there are several factors that allow you to tweak the point at which knock occurs such as chamber size and shape, engine temp, intake temp, bore stroke ratio (longer stroke engine resist knock a bit more because of increased cylinder wall area to cylinder mixture volume which tends to slow detination) and so on. Auto makers strive to get CR as high as possible in a gas engine as current fuel will allow because thermal efficency (amount of usefull work extracted from a gallon of fuel) increases with increased compression ratios but fuel quality is a limiting factor (better fuel is availble but most do not want to pay for it) and while it is also true the higher compression ratios increase NOx formation, that can be controlled largely with catlysts and a bit of timing tweaking too at times. With direct inject for gas engine on the horizion and seeing some limited use today in a few imports, this will all change some because by injecting fuel into cylinder just before ignition it cools the mixture in cylinders and reduces knock potentail and allow a point or 2 or even more of a increase in compression ratio with increased effiecency (from 9 to 10 to 1 or 11 to 1 or more for example) and better MPG and power from higher CR and better MPG also from less loss of fuel to cylinder scavanging as with current systems and a reduction in unburned hydrocarbons as well that the scavanged of fuel in current system can add to. The main reason that diesels get better MPG most of the time is because they have much higher CR ratios than a gas engine (yes it is needed to ignite fuel but it also increases thermodynamic effiecency too) and the fuel itself has about 12 to 15% more heat/energy content per gallon than gas does too. Did you also know that the octane requirement of a engine decreases with increased altitude? There is a LOT that does not meet the eye in overall engine design and operation that people take for granted.