What commands are given to the VVT at or near 3200 RPM

[gmcman]

So with this ongoing occasional noise I get in the valvetrain, something has been constant lately and it sounds like some clatter at or around 3200 RPM during normal acceleration. If I accelerate from a stop and pass through 3200 RPM with a shift happening around 3500 RPM, I get a light racket in what sounds like the valvetrain. After I'm at speed, if I downshift to try to duplicate this it's quiet, it's only as I'm accelerating from a stop and it seems to be in 1st and 2nd gear.

At first I thought maybe a flexplate as the torque is higher at a lower ground speed and could affect the noise if it were cracked. However it seems to be coming from the top of the engine.

The other option may be a cam phaser...I'm curious what the PCM commands for the VVT at this speed from a stop...which seems to be right before a shift but not always will it shift if I have a high throttle setting but the noise is generally still present. If I go WOT sometimes I don't hear anything and sometimes it's very brief.

Sometimes I hear the noise at idle and with raising the RPM slightly it goes away completely.

If at a stop, I can raise the RPM to 3200 with no noise.

Just curious what the cam phaser is commanded to do under these circumstances....if anything.

 

[littleblazer]

I'm not entirely sure but I believe the cam advances as you get up higher, I don't think it's full advance either maybe half and I would assume it backs off advance as it shifts just like timing. Just a guess though.

 

[Mooseman]

One way to find out would be to hook up a Tech 2 and record a snapshot of what's going on with the VVT.

But, I don't think it's anything with the VVT itself. All that does is change the exhaust cam angle and valve timing. Could be a lifter or possibly the timing chain, IMHO. Interestingly, my 5.3 is doing the exact same thing, sounding like a sewing machine between 3000 and 4000 RPM only during acceleration, sounding like it's coming from the top passenger side. No VVT in this engine. I suspect a dying lifter.

 

[Nexus1155]

It issssss the waterpump and clutch fan. Had it plague me for some time until the coolant started pissing out. Sounds as if a loud vibration from maybe the exhaust or torque converter and only seems to happen at that rpm alone. Enjoy! Give that clutch fan a good wiggle up and down left and right and let me know how you make out.

 

[mrrsm]

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