Cadillac Repair: loud knocking, engine knocks, hesitates

Question
i have a 1985 cadillac fleetwood brougham 4.1 liter. the car starts and runs fine but when i hit 45-50 mph and come to a stop or slow down a lot and then try to accelerate it makes a realy loud knocking noise and it hesitates on gaining speed. if kept at 35-40 mph or below it runs fine what could be the problem

Answer
Hi Alex,

     There are several things that might be happening to contribute to all the noise or hesitation and each needs to eliminated as a possable cause.

     (1)Engine main bearing will make a loud knocking noise but won't affect the accelleration.

     (2)The timing could be wrong or the air door in the aircleaner houseing could be closed and that would cause a ping or knock depending upon how hard you accellerate. It is a top-end noise and will affect accelleration.

     (3)The torque converter bolts can loosen up on the flywheel and make a knocking noise only.

     (4)1 or more rocker arm supports could be broken and that will affect both.

     (5)1 or more lobes on the camshaft might be going round and that will show up as poor accelleration and popping through the throttlebody on accel.

     (6)The fuel pressure might be lower than 12psi and can cause accel. problems.

     (7)Might just need a major tune-up. A bad/burned cap to coil rotor button can cause running problems.

     As you can see there are several things to check and it might be best to have your mechanic do the tests and see what is happening so you don't spend money on a car that might turn out to be a money pit. Bill