Engine Shaking, Ready To Give Up On My S80

[boosted5cyl]

You don't normally test compression with an idling motor. It's meant to be done with ALL plugs out, throttle open at cranking speed (around 300 RPM). As pointed out your readings are even, but given that they were not taken at full throttle the differences across the cylinders may not be apparent. 160psi is the bottom of the spec for this motor so personally, I would do the compression test again to be sure you have accurate data. Both in terms of the individual psi readings and the difference across the cylinders. One thing to keep in mind is that if the ignition is on for more than two mins and the motor does not start, the computer will cut control to the throttle. So remember to return the ignition switch to the 0 position. My approach is to do read all cylinders three times and average the three readings for each cylinder. This isolates many variables and ensures repeatable, comparable results.

Other sources of vibration...
Harmonic balancer pulley
Flywheel
Something on the serpentine belt driveline.

You need to get those codes pulled as they may well contain a clue as to whats going on here....
Oil in the plug hole could be simply leaking from the seam between the cam cover and head, or a leaky oil cap seal

Can you post that video somewhere?

[renzo86]

Boosted5cyl: Now that I think about it... Since I replaced my alternator and battery at the same time, I always get this message for low voltage... Then when I press on the gas everything settles down... Can this have anything to do with the harmonic pulley??? I think so. Right now I'm watching videos about it and the idea just came to my mind. I did the compression with all the plugs out. Maybe you are right, I should've taken measurements at least three times each cylinder. I'll try that this weekend.

Is this possible????

@Steve: I checked and inspected all vacuum lines when I replaced the PCV oil trap. I put new hoses and clamps all around. Also checked pipes for leaking air.

[boosted5cyl]

Low voltage could be....well an actually low voltage which could explain rough running, these cars do NOT like anything borderline in the electrical supply. It also may be a result of the alternator change,, I believe there is a part that needs to be changed with the alternator (external regulator?) otherwise you get the message for low voltage when in fact its fine. Time to slap a multimeter on the battery

The harmonic dampener is just a dampener, the belt doesnt acutally run on the dampener pully.

[renzo86]

Where is the external regulator located?? Do you have a diagram for it?

[renzo86]

By the way, how can I check the harmonic balancer pulley?? Do I necessarily have to do a timing belt replacement? If so, any tutorial somewhere?? Sounds like a challenging project!!!!

[steve850]

Good to hear about the vac lines, that's one thing out of the way ( you hope!). The harmonic balancer is basically a counterweight to offset the mass of the flywheel, and the flywheel is basically a heavy plate that carries enough energy in the form of "spinning momentum" as it were, to keep the engine running evenly between each cylinder's power stroke; so a problem with either could cause a shake at idle.

For the alternator issue, make sure you have at least 13.5v at the battery terminals at idle. It shouldn't change much as you increase the engine speed.

You can take the serpentine belt off and run the car for 15 seconds to see if it still shakes, although I can't really see that anything running off that belt would be enough to bind up the engine to that extent without breaking the belt...