Engine knocking sound...very worried!!!

[leofig]

Hi everyone; I noticed a knocking sound on my 2002 Surburban Z71 a few weeks ago when I first cold started it, but it goes away shortly after. Yesterday, the same happened only that it happened again later on and it hasn't gone away. It seems to come from the lower part of the engine.

I always used premium gas (93 octane) and change oil at 2500-3000 miles intervals, and the oil pressure has been around 40 psig, regardless of whether it is iddling or running. Is this normal?

What can be causing the knocking sound? Please help.

Thanks in advance,

LeoF.

[GMMerlin]

Originally Posted by leofig

Hi everyone; I noticed a knocking sound on my 2002 Surburban Z71 a few weeks ago when I first cold started it, but it goes away shortly after. Yesterday, the same happened only that it happened again later on and it hasn't gone away. It seems to come from the lower part of the engine.

I always used premium gas (93 octane) and change oil at 2500-3000 miles intervals, and the oil pressure has been around 40 psig, regardless of whether it is iddling or running. Is this normal?

What can be causing the knocking sound? Please help.

Thanks in advance,

LeoF.

I very rairly reply to the cold start knock threads, but this may be heading in another direction.
First off, how many miles on your engine?
Secondly is this knock only heard on cold start up or now as you describe..happening anytime the engine is running?
If it happens while the engine is running, does it increase and decrease severity with engine speed?
There is a concern about the "cold start knock" or "piston slap" on these engines...a lot of people have alot of opinions about it and I'll leave it as that..
What concerns me is that you state the engine knocks all the time...if so, this is a problem!

Also.....save yourself a lot of money and stop using 93 and go to 87...GM vehicles are designed to run on 87

[leofig]

I've 68k miles. As of now, the knocking occurs constanly; however, there's not increase in noise level as the rpm increase. It almost sound like the noise come from other part other than the engine itself; in other other words, there's not harmony between engine sound and the knocking sound...when the engine is running (say 50 MPH) and I give it a suddenly push the gas pedal, the knocking noise or raddling can be heard separetaly; I hope you can understand me.

Thanks for you prompt reply.

LeoF.

[gregory914]

My 97 burb has 110k miles on it and has had cold start knocking from day one. The service writer at the dealer told me it was normal?? The shop foreman told me off the record it IS piston slap and most of this vintage 5.7s have it. They, "GM", will fix it, but only if the engine blows completely.

Over the life of my burb the knocking hasn't gotten any worse or any less. I have always used Mobil 1 from the third oil change on (10k miles) and change it every 5k miles. My one neighbor told me I had a rod knock the second day I had the truck and the motor wouldn't last past 2500 miles, I guess he was wrong. And I do bust his chops about it every time he looks at my 110k mile beauty. He bought a Jeep because of my "rod knock".

I do agree with MERLIN, but not with the 87 octane statement. I have monitored my fuel consumption for almost all 110k miles and I do get up to 3mpg better fuel economy with 93 octane (if you can use the word economy when desribing a burb's use of fossil fuel!).

Just read your last comment after I entered the comments above and what's important to know is if the knock is there when the car is stopped and does it change with the speed of the engine's rpm. I have VW new Beetle and the fuel pressure releif valve makes a sound just like a rod knock but doesn't change with the engine speed or vehicle speed because the fuel pressure is a constant and the valve opens and closes to return fuel to the tank. I don't know if GM fuel systems work in similar manner?

The Volksie dealer was talking about changing my engine until their Fuel Systems Expert came in from New Jersey and properly diagnosed the problem.

[leofig]

When the truck is stopped, one can heard the knocking; it sounds almost like a plastic paddle were touching the fan blades when running. As I accelarate (still stopped), the noise increases. In the begining, it faded out after a couple of minutes, but now is constant.

On the subject of the 93 vs. 87; I tried 87 before and after a month of using it, my truck started to stall from time to time. The dealer recommended a new fuel pump (since I did not tell them about the gas). As soon as I switch to 97 and added some STP, the problem is gone.

[leofig]

I'm sorry; I meant to say 93 octane and not 97.

[gregory914]

Fuel first- change your fuel filter today!

With the engine off, look for a thread or piece of rubber coming off from the belt then look around the fan shrouding to see if something is hitting the fan. I always try the simple causes first then go from there.

It could be many different things you just have to try to find out exactly where it's coming from and that should lead you to the problem.

Other things to look at: fan, fan clutch, pulleys, belt tensioner, alternater, power steering pump, flywheel cover,water pump and don't rule out a fuel injector problem or something to do with the fuel sysyem. The first time I took my burb back to the dealer for the piston slap, the service writer told me it was probably a "noisey injector". Mine was not but yours may be, which is why a new fuel filter would be money well spent first. And it will improve your running/stalling problems but it could also end your knocking.

[leofig]

I changed the filter two months ago. The noise seems to come from the lower back of the engine. I'll check for other things.

Thanks.

[gregory914]

Try to figure out exactly where it's coming from and that will help in the diagnosis. Back of the engine could be distibutor/rotor or flywheel, but if it's inside could be bad things. Maybe Merlin may have ideas, I only quote from my own experiences.

[leofig]

I took my truck to the local dealer. They told me that the noise was not related to the TSB w/o even writing a ticket and advise me that it will cost me between 3-4 service hours ($200-$300) for the diagnosis along because they had some engine teardown to do first.

Because the truck is out of warranty and not extended is available anymore; I opted for calling GM directly and presented my problem to them. I was surprise that they are willing to work something out. They recommended taking it back to any dealer and letting them determine what's making the noise.

Monday - Dealer advise of possible rocker arm problem and checked; negative;
Tuesday - They advise of possible flywheel problem; negative;
Today - They are still investigating.

When I first heard this knocking was two or three month after I purchase the truck back on March 2002; I mentioned it to the service advisor on one occasion during a routine service appointment, but I was told it was normal. The noise was never documented and at the time the TSB was not even out.

According to this dealer's tech; the noise is the same noise mentioned in the TSB, but they just can't pinpoint it. Meantime, GM is waiting on an answer from the dealer to make a decision. If the word is that the problem is directly related to the cold start knocking and has become worse, I think they are going to cover it.

The service advisor says that they have dealt with similar problems in the past and GM has granted an extended warranty to cover for the damaged or troubled components...I'm keeping the faith and my fingers crossed at the same time.

Later.

[frootl00p3]

What happened? I have been having the same problem with my Suburban. I toook off the valve cover and found a loose lifter, but doubt that is the whole problem, just think that is my clapper.
Jodi

Originally Posted by leofig

I took my truck to the local dealer. They told me that the noise was not related to the TSB w/o even writing a ticket and advise me that it will cost me between 3-4 service hours ($200-$300) for the diagnosis along because they had some engine teardown to do first.

Because the truck is out of warranty and not extended is available anymore; I opted for calling GM directly and presented my problem to them. I was surprise that they are willing to work something out. They recommended taking it back to any dealer and letting them determine what's making the noise.

Monday - Dealer advise of possible rocker arm problem and checked; negative;
Tuesday - They advise of possible flywheel problem; negative;
Today - They are still investigating.

When I first heard this knocking was two or three month after I purchase the truck back on March 2002; I mentioned it to the service advisor on one occasion during a routine service appointment, but I was told it was normal. The noise was never documented and at the time the TSB was not even out.

According to this dealer's tech; the noise is the same noise mentioned in the TSB, but they just can't pinpoint it. Meantime, GM is waiting on an answer from the dealer to make a decision. If the word is that the problem is directly related to the cold start knocking and has become worse, I think they are going to cover it.

The service advisor says that they have dealt with similar problems in the past and GM has granted an extended warranty to cover for the damaged or troubled components...I'm keeping the faith and my fingers crossed at the same time.

Later.

[bpalmer]

Lifters have a tendency to knock on startup if the oil level is too low for them to fill up. Mine did this. Hope this helps.

[frootl00p3]

A GM Mechanic told me "off the record" to try using this stuff called Sea Foam. Pour it directly into the Oil, the whole Pint. Drive it around for about 30-40 miles and then change the oil. This stuff is a Marine product that is petroleum based that is good for cleaning out clogs or sludge in the engine and valves or lifters. My 99 needed two treatments, apparently my Dirt and Gravel road hasn't been so friendly to my engine, could also be my laziness on the oil changes . Anyway it has helped quite a bit with the lifter knocking sound on start up. I picked up a third bottle and added it to my gas tank, it got rid of the pinging on acceleration up hill. I still think I am probably going to have to take it in to the dealership and spend some money on it at some point, but that is my payback for not taking care of my car in the first place. Until then It is running really good right now. Unfortunately I have two kids and a husband who goes to sea too often. I need to make sure my suburban is back up to dependable like it was before I stopped taking good care of it.
The seafoam stuff works well, at least I have been happy with the results. I found it at Napa, but I didn't really search around for a cheaper place. I am not found of knocking noises in my engine. Good luck!

Originally Posted by bpalmer

Lifters have a tendency to knock on startup if the oil level is too low for them to fill up. Mine did this. Hope this helps.

[nflo555]

Merlin,

Hope you will enterain an answer to my Suburban's knocking.

Info on my Suburban:
2003 5.3L
68k miles
Z71
Oil changed every 3K
87 octane
Lucas Oil Stabilizer at oil changes
Wix oil filters

Issue: Knocking only occurs on cold start and reduces in noise when put into gear then eventually goes away when the engine is warm.

Thank you for your time!

[glenncof]

nflo555,

I have 97 tahoe 5.7l at 138K miles. 3K oil changes with 5-10W30 GTX dino Castrol. I have done 3 runs on Syntec syth Castrol 5W30. Never detected knock at cold start. It consumes zero oil in 3000 miles so it's good shape.

Recently I put in Mobil 7500 blend 5W30 and have mild knock when I start drivingfor ~10-15 seconds. It may even knock at cold idle. I'm in N. California. I assume in my case it's the M7500 just being (too thin) thinner than the Castrol 5w30. <It should not be.>

This type of knock typically comes from the lifters having insufficient oil and collapsing. It's often related to anit-drain back valve on oil filter allowing it to drain. The use of thicker oil and cold temperature exaggerate this problem since it takes longer to get oil to the lifters.

In your case you don't say what viscosity you are using nor the temperature environment. Consult user manual. Why use the Lucas ?? Is it a thickner ? I would avoid additives.

Also try changing oil filter especially if mounted horizontally. Look for one with red silicon anti-drain back valve but LOOK at the filter you are buying, not what the manufacture SAYs.

loefig,

You wrote, "before I stopped taking good care of it. " I have done 1000 mile oil change cycles to clean out dirty engines. I would stay away from any washing type additive, it can have sever consequences. Maybe you were just looong overdue for oil change.

I did have 5.7l once that was so worn the lifters would colaspe upon acceleration at temperature. First just knock on light accleration and worse on heavy. BTW, it was a 1975 Pontiac Firebird and was known for this issue. Mileage was 98K as I recall and had good maintentance.