I smoothed out the death rattle by….

So here’s a weird one.. I’m working on a car that has the notorious death rattle. I decide to do a compression check via tech stream (although I can never get this to run properly) while the engine is shaking violently and what do you know, the engine runs smooth as silk as soon as I turn on the test.

As soon as you stop the test the engine goes back to rattling like a car possessed. I look at the live stats while running this compression check and the fuel pump is still engaged, Vapor in the fuel lines, injectors are still firing, And the coils are still firing.

the only difference I see is afs voltage b1s1 is at 4.95 volts during a compression check where as disengaging the test it falls flat on its face down to near zero volts, which I assume is either a rich or lean condition causing the car to stumble.

This almost sounds like it’s a fuel mixture problem. I’ve had several cars have this violent shaking problem with no resolution, and every one clears when running the compression check action in tech stream while the cars running.

Any additional input as to why this Would happen? I’m all ears.