Engine Loses Power and shakes?

Question

Starts great, idles, accelerates great. When you get to 45-50, it starts losing power and shakes like it's going to shake right off the mounts. Will now do about 30, floored in third gear. Pull over, it settles back to a good idle, all over
again,...accelerates up to 45 and then starts losing power.....

Changed coils, wires, pluge, carb, catalytic converter, distributor. Went to points, wired coil directly to the battery. No diff. Checked fuel pressure and volume.
Dodge slant 6 , manual trans van, '84. Doesn't smoke, was good workhorse. I know what fuel starvation is like. It doesn't shake violently. Same with spark interuption. This engine SHAKES bad when it starts losing power. It's got everybody stumpt.

Answer 1

Transmission and clutch plate. When was the last time that you had them replaced/checked. Does the engine sound as though it is working a bit harder that usual around the 45 mark or does it sound like it's power isn't going to your wheels?? What are the rpm's telling you?

Answer 2

The ignition coil must be wired through a "ballast resistor" before it connects to the battery or it will draw too much current from the battery. The hot engine idle is most affected by engine vacuum (you should be measuring almost 20 in Hg on a vacuum gauge at hot idle) or loss of vacuum by vacuum leaks through any bad hoses, vacuum diaphrams, engine gaskets etc. Also, engine timing retarded engine timing will cause a rough idle. So you need to plug the spark advance vacuum hose on the distributor and check the crank shaft timing mark with a simple timing light driven off the number one spark plug. Rotate the distributor to set to the correct timing advance. Make sure your carb choke is opening fully.

Answer 3

Disconnect the exhaust pipe from the manifold and try it. I have run across cases in which the inner wall has collapsed and created the same type of restriction as a stopped up catalytic converter. This is a long shot, but it would be the next thing I would try, Just before taking it to the dealer to get it put on the dyno to check it out with a diagnostic machine.
It could be weak valve springs, but that will show up on the dyno test.

Answer 4

These engines require a valve adjustment. Hardly anyone ever does this. You should, though. Try removing carburetor top, and cleaning out the accelerator pump and metering jets and valves. I would be suspicious, also, of a leak in your fuel pump diaphragm, causing loss of pressure at higher speeds.

Answer 5

Are all your u-joints and drive shaft in good shape? If a u-joint is bad, it could be that at that speed, it is binding causing the shake and power loss (from the binding friction). I know this isn't likely, but just trying to help by thinking outside the box (or engine compartment).

Answer 6

if it shakes then its choking, check the fuel pump and filter