'89 LeSabre with a vibration problem stumper

A friend has a '89 LeSabre with a strange vibration problem that is stumping everyone.

A vibration that gets progressively worse as speed increases. Car becomes all but undrivable by the time you reach 50 mph.

Car has under a 100K miles and well maintained.

The vibration is there under power or coasting in neutral.

At slower speeds there is a definite lop feel like an egg-shaped tire.

He has changed out the wheels and tires and balanced all very carefully.

He has installed new brakes - pads & rotors on the front and shoes on the rear.

All suspension parts checked and tight.

Installed new CV joints.

The vibration remains unchanged.

Anyone have a clue or new direction.

Why is it problems in this forum always seem to occur at the same time? 2 weekends ago, it was water pumps, like 5 threads, the day after I had to change mine. Last weekend it was transmissions. This weekend... this weird vibration problem.

I don't know... occilation you mention, of the car almost bouncing up and down, makes it unlikely that it is the engine. Due to the fact that it's side mounted, occilations from the engine would more likely make your rock.

It almost sounds like the transmission is surging. Providing power hard to the wheels, then dropping out for a couple seconds, and repeating. That could cause the car to hop, similar to pumping the brakes when coming to a stop, but in the opposite direction.

Bouncing a car from inside the frame takes a lot of force... it takes a lot of force just to over-ride the dampening effect of the shock absorbers. Power surging on and off the wheels is the only thing I can think of.

I take that back. Have you checked the fuel filter and the fuel pressure to the fuel rail. If your engine is getting fuel in surges (as often happens with a dying fuel pump or a clogged filter), then it's RPMs would bounce up and down. That would in turn cause uneven power to the transmission and thus to your wheels.

This may not be noticed when idling in the driveway with the hood up, because the engine does not need that much fuel. However, after driving down a road at 45 MPH and slowing to the stop, the engine would have more problems getting adaquate fuel to maintain idle, as it had been subjected to driving requiring greater fuel consumption.

In addition, if ports on the fuel rail are clogged, a fuel injectors is bad, a spark plug or wire is bad, then you would only be getting power from certain cylinders. Thus your engine would spin fast when pistons fired correctly, and choke when other pistons did not.

To amplifly this effect to the level you are suggesting, I would expect it would need to occur in common TDC (top dead center) pairs or triplicates. Such a pairing would be most likely if one of the modules of the Ignition Control Module fried. (I.e. Where are the spark plugs connect in pairs.)

Now the other guys vibration problem... that sounds more like... the whole car shakes and rattles like it's going to come apart. Coupled with stalling out, that's almost certainly a sensor problem or a fuel supply problem. IMHO, whenever an engine stalls it's oil, gas, electrical, coolant, sensors, in that order. LOL

Anyway, anyone else have opinions on my opinions? Anyone wanna tell me I'm full of bull, because there's probably a good chance I am.

Anything that involves a transmission, I hate automatic transmissions, I can never tell if they are working or not. I also hate glue, just so you know.

I appreciate your response. Truly, any feedback could mention something overlooked. However, as my subject header says it is "A Stumper."

Unless my friend is misleading me he states that; "The vibration is there under power or coasting in neutral."

That alone would seem to remove any relation to an engine misfiring problem.

I heard that these creatures use hydraulic or viscous engine and transmission mounts. Anyone have experience with these causing problems.

Umm... the mounts on my 1995 Buick use standard rubber bushings to absorb any vibration from the engine or jolts from the frame.

A "hydralic" or "viscous" solution mount would involve something resembling a shock absorber. I don't think I've ever seen any such thing in a standard consumer vehicle.

I didnt see allignment in there.. or Ignition module.. checks.(replace from junkyard one). ignition wires correct.
Put the car on jacks, start it, put it in gear, NO gas edal.. Inspect for vibration.

One thing to try is taking the car for a drive and have some one else in another car watch the front end of the car, especially what the front wheels are doing. Also I am not sure what the 89 has for front air dams or shields, but they could also flap and cause vibrations.