Rumbling and shaking...?

[Blue90]

Hey guys I've got yet another conundrum...
90 K5 Blazer
Bought it 10 months ago, the seller told me it was a blueprint motor with only 30k on it, but after my extended examination it looks like a rebuilt motor, but I cant verify either way...
Trans could be stock but I'm not sure.
This is honestly boggling me, but here is the gist of what's happening.
Randomly...
Only at stops (traffic lights and so on ....randomly, but relatively often.) There is a vibration that can be felt in seat and steering wheel, and petals. It's not violent by any means, but its noticeable, and concerning.
I've mildly experimented with it by placing it in neutral at the light for 5-30 seconds.
5 seconds had no effect on the vibration.
30 seconds seemed to make it dissipate, but I cannot say that would happen every time.
My guess is the torque converter? but that honestly its a shot in the dark.

Any ideas?

 

[MEANSTREAK K30]

It could be bad motor mounts/ transfer case mounts. You say it only happens at a dead stop? possibly the transmission bolts have loosened slightly from the engine?

 

[paratrooper307]

Mounts would be the first place to check. I put poly mounts in mine, and at some RPM levels it resonates a little because they're a lot stiffer than the factory ones.

I believe all Blueprint engines are rebuilt, as opposed to a new casting like a Goodwrench.

 

[Blue90]

It could be bad motor mounts/ transfer case mounts. You say it only happens at a dead stop? possibly the transmission bolts have loosened slightly from the engine?

Yes only at a dead stop. Dosent speed up or anything as a accelerate away, just sitting still while in drive.
These are things I've only visually checked. Tonight I'll verify and replace if I see any concerning mounts / loose bolts.

 

[Blue90]

Mounts would be the first place to check. I put poly mounts in mine, and at some RPM levels it resonates a little because they're a lot stiffer than the factory ones.

I believe all Blueprint engines are rebuilt, as opposed to a new casting like a Goodwrench.

I'll check the mounts tonight, I've only visually inspected them so far.

Ah ah, makes sense. I was under the impression they were the same as a crate motor, but I honestly don't know.

 

[Blue85]

Could it be misfiring? Maybe the O2 sensor is cooling and it's going open loop?

 

[Blue90]

Could it be misfiring? Maybe the O2 sensor is cooling and it's going open loop?

I've checked and don't see any codes but I suppose it could be doing this and not throwing a code?