Can I backflush an oil pickup screen

[i6pwr]

Motor on 02 Envoy has intermittent knock, not bad when warm, can't really hear it when cold...but from about 3 min after a cold start until hot there's a knock or tap but I don't think it's a rod. The motor is the 4200 Vortec Inline 6.

I have cut open last 2 oil filters and there is nothing but some slight black grit deep in the peats and only in a few pleats, don't see any distinct metal bits or gold.

The oil pressure gauge isn't a real gauge but it's slightly slower to rise then from about a year ago. I change oil realistically every 5-6K, mostly synthetic.

I want to say the noise is in the valve train, I don't really hear it underneath as much but mainly around or just below the valve cover.

I pulled the coil packs one by one and zero change in pitch, I even pulled the coil in the previous firing sequence and still no change.

I have just changed the oil to Castrol Edge and I want to say when the engine is hot, that the noise isn't as pronounced. To remove the oil pan is a major PITA on this vehicle especially with 4WD. I was thinking I could possibly install a sandwich adapter at the oil filter housing and reverse flow some solvent into the oil pan without damaging any seals.

I don't know if there is a one-way valve in the pump but would this be possible? I figure if I could do this and knock some debris out then maybe it's an oil starvation issue. I can open the oil fill cap and see a good film of oil hanging on to the front of the cam phasers but anything is possible.

Maybe drain a quart and add 1qt of ATF,I really don't want to pull the pan but if I do I'm going all out and pulling the timing cover and changing the pump....MAJOR PITA.

 

[Chris142]

no. theres no way to push oil backwards through the pump.

 

[Trav]

Stop before you do some damage. A plugged screen is highly unlikely going by what you said.
Pulling coil packs on a energized ignition system is a good way to pop the ECM.

A lot of things could be causing the noise including carbon knock, a sticky lifter/lash adjuster, rocker arm, piston slap, VVT issue, injector, the list goes on.
You need to get this vehicle on a scan tool/scope and check it out. Check the oil pressure with a mechanical gauge, electrical ones are not all that accurate.

Make sure there are no codes and the ignition is working properly, the injectors are working properly then pin point the noise.
It could be something or nothing more than carbon knock. Carbon knock and piston slap or very common on the these engines but it cant really be accurately diagnosed over the internet, just best guess.

BTW Seafoam does not help with carbon knock you need to soak the pistons with a product available from the dealer.
Yes there are ways of cleaning the pickup in the engine without taking it all apart but i think you would be wasting your time.

 

[Cujet]

I vote for piston slap as the most likely cause, or as a distant second, very mild wrist pin knock. Valves are typically a tick and nearly everyone knows what a ticking lifter sounds like.

Since you claim it subsides when hot, it's very unlikely to be a rod knock.

You can try a higher viscosity, high mileage synthetic to see if it changes the sound characteristics.

 

[turtlevette]

Originally Posted By: i6pwr
I was thinking I could possibly install a sandwich adapter at the oil filter housing and reverse flow some solvent into the oil pan without damaging any seals.

I don't know if there is a one-way valve in the pump but would this be possible? .


You won't be able to back flush a stationary pump, because it's positive displacement. On the old engines that drive the oil pump with the distributer you just pull it, put the primer in, and run the drill both ways. I did that on my old trans am.

 

[Cujet]

Typically, the use of synthetic significantly reduces or eliminates sludge. Since you say you use syn, I suspect your oil pickup screen is clean.

 

[i6pwr]

I was able to get a video and a pic of the filter media. I don't have a hot engine vid but I agree it doesn't sound like a tick but the noise is at roughly 4-5 per sec which is cam speed with a 600 RPM idle.

The exhaust bolt in the very back is broken but doesn't sound like a leak. I'm aware of the piston slap issue with this motor but I never really heard it, was extremely faint if at all when cold.

I used a stethoscope and around #4&5 I could hear what sounds like an xylophone and could be the noise I'm hearing while likely muffled on the outside.

The filter media is practically free of debris, I will get a real gauge on it this week but this motor has had a cold start tick and is most present on cold days with fresh oil, doesn't tick all the time but my fingers are crossed it's a lash adjuster.

I didn't pull a coil pack but the harness when testing.

 

[i6pwr]

This is an audio clip through the stethoscope. Sounds like a piston or pin but not sure if it's related to the knock.