Noise when highway driving...no CEL???

[MLRTYME]

Hello all,

I have a 2007 Denali with the 6.2L engine. Truck has 131K miles and has been serviced regularly (every 3k) for it's whole life. I do have the piston slap at warm up, but no bad sounds or other issue to speak of. No CEL or codes thrown...so I'm stumped.

When driving around town (stop and go), the truck operates fine. Even in the Phoenix heat, things are okay. Oil press at cruise is 35-37ish...and around 11 at idle. A little lower than normal, but nothing so bad that I'm freaking out. No knocking/pinging to speak of. However, the past 2 times I have driven on the highway for 25+ miles, the truck develops a noticeable ticking/pinging sound. No loss of oil pressure, no CEL. It does not sound like a rod/main issue...higher pitch than that. Also, the sound only exhibits during cruising efforts (steady 65-70mph). If I get off the throttle, the sound goes away. When I apply a reasonable amount of throttle, the sound goes away. Maintain that speed, it comes back.

Here's the weird part...when both times...when I got off the freeway and proceeded to drive stop and go, the sound went away. No change in temps in the engine/transmission (tranny was 201). I do have access to a Tech2, but honestly wouldn't know what I'm looking for.

Any ideas from anyone?????

 

[OR VietVet]

Maybe have a problem with an exhaust manifold leak. Maybe there really is an oil pressure problem. What type and brand fuel do you use? How old are the tune components?

 

[MLRTYME]

Maybe have a problem with an exhaust manifold leak. Maybe there really is an oil pressure problem. What type and brand fuel do you use? How old are the tune components?

I cannot see anything that would show an exhaust leak (no broken bolts on the manifolds or collectors). I asked my engine builder who said that some of those years struggled with oil pumps and the internal pressure check valves. I use the same fuel (Circle K and Frys fuel) that I have used successfully for the past year. Once every 4-5 fills I do Lucas fuel system cleaner...just for insurance purposes. The tune has not been altered and all the components for fuel/spark/air/cam/crank monitoring are stock...as far as I can tell.

I have not tried to flush the engine...I think that will be the next effort. However, I watched the gauge like a HAWK the second time it occurred, and saw no decrease in pressure when the sounds started. I also thought about fuel since it was happening when warm...and it seemed that decreasing the fuel level (off the gas) made a change and adding fuel (applying throttle) made a change. Both instances have happened with the same tank of fuel. I'll go add some better fuel and see where that takes me as well.

 

[OR VietVet]

If by tune components being "stock", you mean original, then change them. I am assuming you mean they are not original but are not anything different than stock application. How old are the tune related components? How many miles? I have heard of horror stories on here about trying to flush the engine. I have also seen where it was successful. What oil and weight do you use? What oil filter? If it is close to oil change time I would do it and see if anything changes. I am not a fan of the oil pressure readings. Maybe has an oil pickup problem?

 

[swathdiver]

Hello all,

I have a 2007 Denali with the 6.2L engine. Truck has 131K miles and has been serviced regularly (every 3k) for it's whole life. I do have the piston slap at warm up, but no bad sounds or other issue to speak of. No CEL or codes thrown...so I'm stumped.

When driving around town (stop and go), the truck operates fine. Even in the Phoenix heat, things are okay. Oil press at cruise is 35-37ish...and around 11 at idle. A little lower than normal, but nothing so bad that I'm freaking out. No knocking/pinging to speak of. However, the past 2 times I have driven on the highway for 25+ miles, the truck develops a noticeable ticking/pinging sound. No loss of oil pressure, no CEL. It does not sound like a rod/main issue...higher pitch than that. Also, the sound only exhibits during cruising efforts (steady 65-70mph). If I get off the throttle, the sound goes away. When I apply a reasonable amount of throttle, the sound goes away. Maintain that speed, it comes back.

Here's the weird part...when both times...when I got off the freeway and proceeded to drive stop and go, the sound went away. No change in temps in the engine/transmission (tranny was 201). I do have access to a Tech2, but honestly wouldn't know what I'm looking for.

Any ideas from anyone?????

That motor will self destruct if you run any less than 93 octane over time, we see lots of broken pistons from folks running 87 across the forums. I would also run Top Tier fuels with the best detergents which also aid in keeping the chambers clean and knock at bay.

11 psi at idle, either the oil pump's pick up tube o-ring needs replacement or something more nefarious is amiss. You can add two more quarts of oil to the motor and see if the pressure comes back up. If it does, it's the o-ring.

What kind of gas mileage are you getting?

I would put the Tech-2 on it and see if you can see the fuel pump's actual and commanded pressure and its trim level. I could not find these things on an '07 Tahoe with a 5.3 but the menu for yours may be different. I would also look at the Long Term Fuel Trims and the four O2 Sensors. The Upstream Sensors ought to be moving up and down pretty regularly and the downstream should be fairly steady. If the downstream sensors are moving a lot, the cats are suspect. Especially if you have a rattle and if the gas mileage is down.

Use the Tech-2 to test your coils and injectors.

When was your Denali built?

 

[MLRTYME]

That motor will self destruct if you run any less than 93 octane over time, we see lots of broken pistons from folks running 87 across the forums. I would also run Top Tier fuels with the best detergents which also aid in keeping the chambers clean and knock at bay.

11 psi at idle, either the oil pump's pick up tube o-ring needs replacement or something more nefarious is amiss. You can add two more quarts of oil to the motor and see if the pressure comes back up. If it does, it's the o-ring.

What kind of gas mileage are you getting?

I would put the Tech-2 on it and see if you can see the fuel pump's actual and commanded pressure and its trim level. I could not find these things on an '07 Tahoe with a 5.3 but the menu for yours may be different. I would also look at the Long Term Fuel Trims and the four O2 Sensors. The Upstream Sensors ought to be moving up and down pretty regularly and the downstream should be fairly steady. If the downstream sensors are moving a lot, the cats are suspect. Especially if you have a rattle and if the gas mileage is down.

Use the Tech-2 to test your coils and injectors.

When was your Denali built?

Well, in AZ 91 Octane is the highest that you can normally get from the pump. Always run that premium in the tank...always! However, I also know that isn't a guarantee of success, and a bad batch of fuel can happen anytime. However, I don't have an Exxon or Chevron close to my home...so I buy the 91 Octane at the local stations. I went and grabbed some 91 from a Chevron just last night...to see where that takes us.

Yes, I'm concerned about the oil PSI for sure. I don't see/hear any other negative issues than the one listed above. As mentioned, up until that specific time on the highway I heard no nefarious sounds or knocking. But as someone that does my own engine work on my other cars/K5, the loss of PSI scares me to death! Cam bearing? Rod/Main getting ready to go? However, I normally build SBC and BBC for street cars or 1/4 mile race applications and rebuilds are frequent, so we rarely see gradual reduction in oil PSI usually. If we lose oil pressure, it is usually because something exited the block! LOL

I will pull the tech-2 out. I have had the truck for a year now and when I initially did the purchase, I ran ALL the tests I could think of. No major misfires or anything else I could see. No major change in MPG over the past few weeks (15.4 as a combo of in town and limited HWY driving).

Question: I am going to try to add 2 quarts and see what happens today. Do I drive it normally with the 2 qts added (I know overfilling can be dangerous in most applications) or just do a start-up and compare pressure to pressure while idling in the driveway? New to these LS engines and if I do need a rebuild, don't want to hurt anything I might need later.

...and the help is very appreciated! Just hoping to have some folks with more knowledge in this area help guide me to the best possible solution. Even if that is pulling the engine and starting from scratch.

 

[OR VietVet]

Add the 2 quarts of oil and idle the engine. Not recommended to drive but a short one around should be ok.

 

[swathdiver]

A guy on here or over at GM-Trucks drove around with the extra 2 quarts for about a year until he could afford to fix it.

 

[MLRTYME]

Well, I just found out that I will be working from home for at least the next month (probably more) so I have decided to just pull the engine and do a full rebuild. This way we can do an autopsy and see if anything nefarious shows up. I added the extra oil and did not see a large differential in oil pressure upon idle. I will also have the tranny gone through (since it will be sitting out anyway).

A big thank you to everyone on the forum here willing to jump in and help me out. New to this type of vehicle (everything else I own is at least 36 years old) and I'm learning to tune with a laptop and not a flat-head screwdriver and 9/16 wrench.

 

[MLRTYME]

Quick Question: has anyone updated their CVN via the Tech2-Tis2000 process? I ordered a reman transmission and they advised that I would need to update one of the systems. I figured I could do this myself with the Tech2...but does that read the most current data from GM, or do I need tis2web or the dealer to get the latest/greatest?

Appreciate any thoughts on this. Found a video that made it seem pretty straightforward. Almost too easy???