2000 5.3 knock, help diagnosing cause?

[demarpaint]

Originally Posted By: clinebarger
That's Piston Slap. Some LS engines are really loud when it's cold!

Like Trav already stated......Fix the misfiring! Your going to ruin the converters if their not already the cause of the misfiring. A flashing MIL means the converters are being harmed.

These trucks generally set a P0101 "MAF sensor out of range/sensor performance" when the converter/s get plugged/partially plugged. But not 100% of the time.

Did you replace the plug wires?
Have the Catalytic Converters checked. You can make a Vacuum/Pressure gauge adapter out of an old O2 sensor.
Check Fuel Pressure.
Check for Fuel present at the fuel pressure regulator vacuum hose.
Spray some carb cleaner around the base of the intake (Where it meets each cylinder head) on a cold start.....If the RPM's change dramatically or makes it run rough, Change the Intake gaskets. They leak when is cold & will not necessarily cause "lean" codes.

Do you have a way to isolate the cylinders that are misfiring? Capable scan tool to watch/log misfire data?
While the Multec II injectors on your truck are not near as bad as the original Multec injectors......Their performance still degrades over time/mileage especially if it sits a lot. I think Trav checks & flows Injectors?


Exactly. I can't see how changing oil brands or grades, or filter brands is stopping a blinking CEL, and misfire.

Yes Trav has an injector cleaning business, and does top notch work! The two of you have pointed the OP in the right direction.

 

[Trav]

Originally Posted By: clinebarger
That's Piston Slap. Some LS engines are really loud when it's cold!

Like Trav already stated......Fix the misfiring! Your going to ruin the converters if their not already the cause of the misfiring. A flashing MIL means the converters are being harmed.

These trucks generally set a P0101 "MAF sensor out of range/sensor performance" when the converter/s get plugged/partially plugged. But not 100% of the time.

Did you replace the plug wires?
Have the Catalytic Converters checked. You can make a Vacuum/Pressure gauge adapter out of an old O2 sensor.
Check Fuel Pressure.
Check for Fuel present at the fuel pressure regulator vacuum hose.
Spray some carb cleaner around the base of the intake (Where it meets each cylinder head) on a cold start.....If the RPM's change dramatically or makes it run rough, Change the Intake gaskets. They leak when is cold & will not necessarily cause "lean" codes.

Do you have a way to isolate the cylinders that are misfiring? Capable scan tool to watch/log misfire data?
While the Multec II injectors on your truck are not near as bad as the original Multec injectors......Their performance still degrades over time/mileage especially if it sits a lot. I think Trav checks & flows Injectors?


Yes, the original Multec were terrible, I have box full of electrically defective ones. They usually Ohm out okay but its the current draw test they usually fail. The failure rate of those and some of the Marelli injectors is astronomical.
The Multec II have another issue and that is some have no filter inside causing them to clog but electrically they are usually okay. Through the rail or in tank cleaning solutions will usually not remove deposits from these.

No doubt it has piston slap what LS doesn't but IMO and as you said the misfire is the real issue that needs to be addressed.

 

[Scdevon]

That's classic cold piston slap. If you can modulate the hollow knock like that with the throttle around 1200 to 1800 rpm, it's piston slap. Basic engine noises 101.

 

[Mc357]

It looks like I have some work to do.
I have not changed my wires, coils, or injectors.
The misfire only happens over 2k rpm, I have been keeping it under that for the most part , hopefully the cat tests out ok.
I do know someone with an higher quality scan tool. I will have to see if I can have him help me to find out which cylinders Misfire. Maybe I just need one or two injectors.