Engine/Spark Knock? [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Engine/Spark Knock?


Chevy Girl
03-31-2009, 02:33 PM
I'm new to this so bare with me. I have a 2003 GMC Envoy sitting at approx. 96,000 miles, when I bought it in August last year it had 92,000. When we got it, it had a slight knocking in the motor, mainly when it was idling. Almost sounded more like a tap so I decided it needed better oil and lucas and it'd be fine since dealerships don't put great oil in them. Over the past 8 months the knocking has become worse and more frequent. It knocks while idling, not loud but audible. It knocks when it is shifting between 1st-2nd and 2nd-3rd the worst. When the RPMS reach about 2 grand and up you'll start to hear it, and heaven forbid you let off the gas while it's making the noise it gets extremely loud. It almost has a diesel sound. I took it to one shop that said Spark knock, I asked about timing, nothing they could do if it gets worse bring it back, a.k.a when your motor blows we'll be glad to rebuild it. Next shop has it a day and says, probably a piston, you need a new motor. Now my boyfriend is a military mechanic and like he said, if it was a piston I'd blown the motor by now b/c I've towed our boat and stuff with it. Someone suggested spark plugs and coil packs. I bought spark plugs, waiting to put them in till I get a second opinion. Another friend mentioned it could be a collapsed lifter. I'm not sure b/c when I sit idle sometimes the truck will actually act like it's going to die, the RPMs will drop below a grand the rocket up to 2200 like someone is revving it and no one is even in the truck. Is anyone else having these kinds of issues? :bonk:

wardak33
03-31-2009, 03:11 PM
It could be both. But you would have more of an effect (like your engine already blown up just like your boyfriend said) if it was rod knock. i dont' know..thats just my opinion. I say go ahead and do the spark plugs since you're close to the point where you have to change them anyways.

The idle issue is most likely a dirty throttle body though. It'll only happen when the A/C compressor is running. thats what you're basically describing. It's a real simple job, only should cost you the cost of the cleaner. Look it up in the articles section. hope this helps!

rbarrios
03-31-2009, 04:33 PM
like he said---
try cleaning the throttle body to see if it gets rids of that funny idle.
(usually happens when the AC is on)....

But the knock-- occur ALL time time- or more when cold 1st thing in the morning...

The I6 engines are prone to Cold Carbon Knock.. they knock like crazy when the engine is cold-- and then goes away once warm...

Chevron techron concentrate (fuel system cleaner) is good for this.
It can help quiet this down.

try both of the above.

Chevy Girl
03-31-2009, 06:53 PM
Thanks guys! I'm going to go ahead and have him help me with the spark plugs, I'm in line after the boat motor haha go figure. I had considered Cold Carbon Knock but it doesn't just do it when it's cold, it can actually get worse after it's run for a bit. Even worse if he drives it. I regularly put Lucas Fuel Treatment in it, every few tanks, and I fill it up with Shell Premium gas ONLY. Very religious on that. After seeing how well my Monte Carlo did with that, I'm stuck now. We do actually put 10W-30 in the truck now along with the Lucas Oil Treatment with every oil change. So hopefully the spark plugs help.

As for the idle problem, it does it with the A/C compressor off. The first time it did it to me in traffic my auto reaction was to turn everything off and then it still did it. We will try the throttle body though just to see.

Super 88
03-31-2009, 06:55 PM
Thanks guys! I'm going to go ahead and have him help me with the spark plugs, I'm in line after the boat motor haha go figure. I had considered Cold Carbon Knock but it doesn't just do it when it's cold, it can actually get worse after it's run for a bit. Even worse if he drives it. I regularly put Lucas Fuel Treatment in it, every few tanks, and I fill it up with Shell Premium gas ONLY. Very religious on that. After seeing how well my Monte Carlo did with that, I'm stuck now. We do actually put 10W-30 in the truck now along with the Lucas Oil Treatment with every oil change. So hopefully the spark plugs help.

As for the idle problem, it does it with the A/C compressor off. The first time it did it to me in traffic my auto reaction was to turn everything off and then it still did it. We will try the throttle body though just to see.

Personally if it were my vehicle, I would do a compression check when you have the spark plugs out!

Chevy Girl
03-31-2009, 08:23 PM
Personally if it were my vehicle, I would do a compression check when you have the spark plugs out!

That's a good idea, thanks! That might give us a big tip on something else being wrong. We've got a compression tester so we'll try that.

Double D
03-31-2009, 10:37 PM
The Lucas oil treatment is not a cure all. It could actually cause the oil to foam. I would clean the throttle body, change the oil to a Pennzoil yellow bottle or Valvoline 5W-30, with either an AC Delco or Purolator oil filter, then add a can of Seafoam(I would actually use AutoRx) but the Seafoam is a good quick clean. Run for 1000 miles, then drain and replace the oil and filter with the same stuff.. Replace the plugs with AC Delco/NGK Platinum or Iridiums. These steps will help the vehicle regardless, but may also help to expose the real issue.

OH, and I would also replace the front O2 sensor.

rbarrios
04-01-2009, 12:41 AM
Interesting.
so if it does it when warm- then cold carbo knock is out of the question.
let us know how the compression check goes.

cdpyjs
04-01-2009, 12:51 PM
I'm assuming there are no SES lights on? Does it seem to have reduced power at all? The statement you made about it getting worse when you let off the gas is concerning. That sounds very indicative of a bearing going bad. When you were towing with it, did it seem worse under load? Unfortunately, our oil press. gauges are more of a dummy light and don't tell us our exact oil psi. I believe early versions of these trucks had a TSB about bad cylinder sleeves. Usually you'll get a piston slap noise with that, but typically that goes away or gets better as it warms up and the piston expands.

Also, the throttle body/idle thing. My truck did it frequently even w/o the A/C on. After I cleaned it, 99% better.
Keep us posted and WELCOME!:thumbsup:

ssmedt
04-01-2009, 12:55 PM
I know that member jsprewell had a cracked exhaust manafold on his envoy and it make a nocking sound throughout the entier RPM range

cdpyjs
04-01-2009, 12:56 PM
I know that member jsprewell had a cracked exhaust manafold on his envoy and it make a nocking sound throughout the entier RPM rangeThat's actually a good thought. And when you let off the gas, the back pressure would make it sound worse....very interesting....:undecided

Chevy Girl
04-01-2009, 06:14 PM
I'm assuming there are no SES lights on? Does it seem to have reduced power at all? The statement you made about it getting worse when you let off the gas is concerning. That sounds very indicative of a bearing going bad. When you were towing with it, did it seem worse under load? Unfortunately, our oil press. gauges are more of a dummy light and don't tell us our exact oil psi. I believe early versions of these trucks had a TSB about bad cylinder sleeves. Usually you'll get a piston slap noise with that, but typically that goes away or gets better as it warms up and the piston expands.

Also, the throttle body/idle thing. My truck did it frequently even w/o the A/C on. After I cleaned it, 99% better.
Keep us posted and WELCOME!:thumbsup:


No, no ses light which is what I found odd. It tests clear, no codes. Power is fine, it gets up and goes. I mentioned the bearing to my boyfriend and he said the sound is more like timing slack, which would obviously cause the valves to chatter. He's quite determined on the timing chain, but it only has 97,300 on it. Under load the truck is fine. I hauled a trailer full of wood and I towed our boat and it just took off and went. Never hestitated or acted like I even had anything back there. My truck does have the tow package. I check on the TSB for the piston sleeve and my truck didn't fall under it.

Chevy Girl
04-01-2009, 06:18 PM
That's actually a good thought. And when you let off the gas, the back pressure would make it sound worse....very interesting....:undecided

Hmmm, interesting thought. B/c really it does chatter while I'm driving, you just don't hear it cause it's ever-so-slight and the tires make so much road noise. I think we may have him look at that tonight while he's outside messing with the boat motor. :undecided

Chevy Girl
04-01-2009, 11:25 PM
Well he just got out there and checked the exhaust manifold.... no such luck. No cracks, no damage. :hopeless Back to searching.

GeorgeJL75
04-01-2009, 11:52 PM
Thanks guys! I'm going to go ahead and have him help me with the spark plugs, I'm in line after the boat motor haha go figure. I had considered Cold Carbon Knock but it doesn't just do it when it's cold, it can actually get worse after it's run for a bit. Even worse if he drives it. I regularly put Lucas Fuel Treatment in it, every few tanks, and I fill it up with Shell Premium gas ONLY. Very religious on that. After seeing how well my Monte Carlo did with that, I'm stuck now. We do actually put 10W-30 in the truck now along with the Lucas Oil Treatment with every oil change. So hopefully the spark plugs help.

As for the idle problem, it does it with the A/C compressor off. The first time it did it to me in traffic my auto reaction was to turn everything off and then it still did it. We will try the throttle body though just to see.

It could be the Premium Gas. Unless you have a tune, I would return to regular 87 octane. I would also ditch the Lucas additives.

Double D
04-02-2009, 12:09 AM
Yes, I forgot to mention ditch the high octane also, lose the lucas, do a cleaning of the throttle body and inside the engine. I actually had a customer with a new Trans am. She was running high octane gas and the vehicle ran like crap, would even shut off. She switched to 87 and the car ran perfect. Really, it is a true story. :o

Chevy Girl
04-02-2009, 12:14 AM
Well it would figure I just filled the tank at lunch today...... :duh: I'll do that next tank though, only takes a few days with my distance from my job. The guys at both auto shops I took it too said to run the higher octane so I decided I'd stick with it. Which Lucas should I be getting rid of? The fuel treatment or the oil treatment?

GeorgeJL75
04-02-2009, 08:15 AM
I would stop using both Lucas additives. Run Techron in the fuel every few months and as long as you are using SM rated oil no additves are needed in the crankcase.

cdpyjs
04-02-2009, 08:29 AM
I would stop using both Lucas additives. Run Techron in the fuel every few months and as long as you are using SM rated oil no additves are needed in the crankcase.

:iagree:

scm
04-02-2009, 09:39 AM
Do you notice any difference between 5W-30 and 10W-30 in the engine on a colder start? Theoretically the 10W-30 would be thicker and make less noise but once they warmed up they would be the same 30 grade. I know a lot of people put a "heavier" oil in older engines to reduce the noise from the valve train. I've put 10W-40 in an older truck engine ('88 4.3L K1500) that called for 5W-30 to quiet down the lifters and rods. Some new engines have all kinds of small oil pumps, tubes, squirter mechanisms to lubricate different parts of the engine that a 10W-40 may clog shut if it starts to sludge as a 10W-40 will break down quicker and flow slower than a 10W-30. I have no idea if our 4.2s have those parts or if a 10W-40 would be safe in our engines so be careful.

This might help you track down the issue if you can notice a difference with different weight oils at start or when hot.

cdpyjs
04-02-2009, 09:45 AM
Do you notice any difference between 5W-30 and 10W-30 in the engine on a colder start? Theoretically the 10W-30 would be thicker and make less noise but once they warmed up they would be the same 30 grade. I know a lot of people put a "heavier" oil in older engines to reduce the noise from the valve train. I've put 10W-40 in an older truck engine ('88 4.3L K1500) that called for 5W-30 to quiet down the lifters and rods. Some new engines have all kinds of small oil pumps, tubes, squirter mechanisms to lubricate different parts of the engine that a 10W-40 may clog shut if it starts to sludge as a 10W-40 will break down quicker than a 10W-30. I have no idea if our 4.2s have those parts or if a 10W-40 would be safe in our engines so be careful.

This might help you track down the issue if you can notice a difference with different weight oils at start or when hot.Personally, I wouldn't use 10w-40 in my worst enemy. That oil is no good. I've seen it destroy engines (several). I know many good mechanics/engine builders and they get sick at the thought of using that oil. Either a 10-30, or 15-40 depending on your application.
As far as the 10-30 vs 5-30, the 5-30 should actually keep the motor quieter at start up. The thinner oil travels faster up to the valvetrain and does not starve it for oil as long as 10w does in cold weather. I wouldn't recommend using 10-30 in these in a cold climate, but I do run it in my other trucks during the summer.:m2:

Super 88
04-02-2009, 11:23 AM
Personally, I wouldn't use 10w-40 in my worst enemy. That oil is no good. I've seen it destroy engines (several). I know many good mechanics/engine builders and they get sick at the thought of using that oil. Either a 10-30, or 15-40 depending on your application.


:iagree: I remember back in the 80's reading an article in Popular Mechanics (I think) saying that GM would void the warranty on an engine if you used 10W-40. Fortunately oils have changed a lot since then, but I do know GM states in the 05 owner's manual "Do not use SAE 10W-40, SAE 20W-50 or any other viscosity grade oil not recommended"

Chevy Girl
04-02-2009, 09:30 PM
Do you notice any difference between 5W-30 and 10W-30 in the engine on a colder start? Theoretically the 10W-30 would be thicker and make less noise but once they warmed up they would be the same 30 grade. I know a lot of people put a "heavier" oil in older engines to reduce the noise from the valve train. I've put 10W-40 in an older truck engine ('88 4.3L K1500) that called for 5W-30 to quiet down the lifters and rods. Some new engines have all kinds of small oil pumps, tubes, squirter mechanisms to lubricate different parts of the engine that a 10W-40 may clog shut if it starts to sludge as a 10W-40 will break down quicker and flow slower than a 10W-30. I have no idea if our 4.2s have those parts or if a 10W-40 would be safe in our engines so be careful.

This might help you track down the issue if you can notice a difference with different weight oils at start or when hot.


Really the only different I see in the 10W-30 we put in is the noise reduction, but it was only the first week or so after we changed the oil, now it's back to normal. I think I may take it back down to the suggested 5W-30 and get the High Mileage SUV I was using. I got good gas mileage with it. The only difference I saw as to the start with the heavier oil is the change oil light stays on a few seconds after start up b/c the oil is thicker. But it goes right off.

Super 88
04-03-2009, 12:24 AM
Really the only different I see in the 10W-30 we put in is the noise reduction, but it was only the first week or so after we changed the oil, now it's back to normal. I think I may take it back down to the suggested 5W-30 and get the High Mileage SUV I was using. I got good gas mileage with it. The only difference I saw as to the start with the heavier oil is the change oil light stays on a few seconds after start up b/c the oil is thicker. But it goes right off.

Hold it. I think you are confused. The change oil light has NOTHING to do with what oil you have in there.
When that light stays on, it is the OLM (Oil Life Monitor) and it means it is time to change your oil - or the light wasn't reset the last time the oil was changed.

The OLM works off an algorithm - it measure engine temp, revolutions, and various other conditions (that is a oversimplification but you get the idea) and figures out when it's time to change the oil. It doesn't know what oil is in the engine, or even if there IS oil in the engine.

The directions for resetting the OLM light are in your owner's manual - but the short version is you turn the key on (do not start engine) push the gas pedal completely to the floor 3 times in 5 seconds.

Chevy Girl
04-03-2009, 08:40 AM
Hold it. I think you are confused. The change oil light has NOTHING to do with what oil you have in there.
When that light stays on, it is the OLM (Oil Life Monitor) and it means it is time to change your oil - or the light wasn't reset the last time the oil was changed.

The OLM works off an algorithm - it measure engine temp, revolutions, and various other conditions (that is a oversimplification but you get the idea) and figures out when it's time to change the oil. It doesn't know what oil is in the engine, or even if there IS oil in the engine.

The directions for resetting the OLM light are in your owner's manual - but the short version is you turn the key on (do not start engine) push the gas pedal completely to the floor 3 times in 5 seconds.



Hmm well that's odd, it didn't start coming on till after we put the thicker oil in it and we'd changed the oil in the truck 2 times before that. Guess it was just coincidence. Someone said it measured the toxicity and thickness of the oil too and that was why it would come on but then go off once the truck warmed up cause the oil thinned out. I don't do well with these vehicles with all these silly lights and dings to tell you gas or oil or whatnot lol, I grew up working with cars you just had to know. I'll try that pedal thing this morning when I get in see if it stops doing it. Thanks!

Double D
04-03-2009, 09:08 AM
You definitely are not doing your engine any favors by running a 10w-30 with the Lucas. If you want to stick with a dino(conventional) oil, I suggest Valvoline, or Havoline 5W-30. If synthetic, go with Mobil 1 or Valvoline full synthetic. All of these are at any store.

cdpyjs
04-03-2009, 09:26 AM
Hmm well that's odd, it didn't start coming on till after we put the thicker oil in it and we'd changed the oil in the truck 2 times before that. Guess it was just coincidence. Someone said it measured the toxicity and thickness of the oil too and that was why it would come on but then go off once the truck warmed up cause the oil thinned out. I don't do well with these vehicles with all these silly lights and dings to tell you gas or oil or whatnot lol, I grew up working with cars you just had to know. I'll try that pedal thing this morning when I get in see if it stops doing it. Thanks!Could it possibly be an oil pressure light? Not sure if we even have one on these trucks, but if it's too cold and the oil isn't moving yet, if we had one, it might come on temporarily until the oil is flowing.:m2:Never heard of that with 10w-30 though, it would have had to been really cold.

Super 88
04-03-2009, 10:37 AM
Hmm well that's odd, it didn't start coming on till after we put the thicker oil in it and we'd changed the oil in the truck 2 times before that. Guess it was just coincidence. Someone said it measured the toxicity and thickness of the oil too and that was why it would come on but then go off once the truck warmed up cause the oil thinned out. I don't do well with these vehicles with all these silly lights and dings to tell you gas or oil or whatnot lol, I grew up working with cars you just had to know. I'll try that pedal thing this morning when I get in see if it stops doing it. Thanks!

I don't know who told you that, but it is completely wrong. The OLM is not that sophisticated. Do a search on this forum and others (like bobistheoilguy.com)

"What happens if the oil is changed and the system is not reset?
Since the GM Oil Life System does not actually sense oil condition, it is important that the engine computer knows when an oil change takes place. By enabling the reset (read owner's manual for instructions), it lets the computer know an oil change has taken place. In the event that an oil change is done without resetting the system, the 'change oil' indicator will remain illuminated until the system is reset."

http://www.gm.com/corporate/responsibility/environment/maintenance/simplified_maintenance_qa_040104.jsp

Could it possibly be an oil pressure light? Not sure if we even have one on these trucks,

I don't think our trucks have an oil pressure light - that's what the dummy gauge is!

lift_r_up
10-26-2009, 01:24 AM
Well he just got out there and checked the exhaust manifold.... no such luck. No cracks, no damage. :hopeless Back to searching.

Hi there been off for awhile and I was just going through this thread and saw this. Now if he didnt find a crack there is a good chance the manifold needs to be resurfaced. Normaly what happens is it will make noise until its warm then go away that wood be a symptom. My truck deos the same thing I havn't done this yet because I just don't have the time what so ever but I'm 99% sure that would be the issue.

Chevy Girl
10-26-2009, 06:51 PM
Hi there been off for awhile and I was just going through this thread and saw this. Now if he didnt find a crack there is a good chance the manifold needs to be resurfaced. Normaly what happens is it will make noise until its warm then go away that wood be a symptom. My truck deos the same thing I havn't done this yet because I just don't have the time what so ever but I'm 99% sure that would be the issue.


Well if it wasn't for the fact that the knocking never stops I might agree. The knocking is constant and gets worse when the truck is shifting gears. I've had 2 shops tell me the piston sleeve has slipped on one of the pistons. Which makes sense. And the I6 in the Envoy is notorious for that and it explains the gas mileage issue and such. Bad thing, only way to really know is to tear the motor apart. :cry:

efi-diy
10-26-2009, 07:01 PM
If a sleeve has slipped enough usually the top piston ring will catch it and then pull the sleeve down into the crankshaft which then comes to a fast halt.

Since its still running I don't think that is your problem. I'd get a microphone stick it under the hood connected to a laptop and record the sound. Then post it here. It'll help diagnose whats going on.

gutzj
05-02-2010, 07:24 PM
Anyone know what the fix for this was? My '03 is doing the EXACT same thing. Thanks!!:confused:

omega0509
05-05-2010, 04:28 PM
:iagree: I remember back in the 80's reading an article in Popular Mechanics (I think) saying that GM would void the warranty on an engine if you used 10W-40. Fortunately oils have changed a lot since then, but I do know GM states in the 05 owner's manual "Do not use SAE 10W-40, SAE 20W-50 or any other viscosity grade oil not recommended"

Hmm. I had a '90 Cadillac Deville with a 4.5L Cadillac (pre northstar) V8 that specifically required 10W-40. That said, for the 2002 Trailblazer the manual recommends 5W-30 for all temps, but indicates 10W-30 can be used above zero degrees Fahrenheit. Anyone have any tips on mitigating the amount of oil flowing down your arm when removing the oil filter?

gutzj
05-08-2010, 09:11 AM
Well, I think that I have pretty much confirmed it is a rod knock. It is for sure not an exhaust leak and it's not carbon knock or piston slap because it never completely goes away even after warming up. I even tried the Sea Foam. The use of a stethoscope has lead me to the rod knock along with a video on YouTube of a running engine with the tranny removed - the sound is exactly the same. I am now searching for a used engine:sadcry: It only had 143,000 miles on it and I was hoping for atleast 250K.

pmatrac
05-08-2010, 09:33 AM
From your description it sounds more like a piston slap then a rod knock. Have you noticed any variation in oil pressure? A rod with wear will usually cause a pressure variation because the clearance between the rod bearing and the crank throw has changed.
Piston slap is caused by wear on the skirt. Again clearance between the piston skirt and cylinder wall has changed. You can run a motor with slap you just wear that cylinder. Is the problem worse when cooler?
Another place to look is pin clearance.
You did not say anyhing about the power level of the vechile.

gutzj
05-08-2010, 05:54 PM
Oil pressure seems fine but these gauges aren't the best or most accurate. Upon start up when it is cold there is VERY LOUD knocking but it dies down very quickly (1-2 seconds) to a quieter level.
The knocking seems to get a tad worse once it warms up. Power seems fine but I have not pushed it or let it wind out since the knocking started. This knocking started all of a sudden with no prior hint of any knocking or tapping.