Having some serious problems. Car shudders under a load. Started off doing it occasionally between 45 and 55 mph now does it all the time. So far i have changed the fuel pump, fuel filter, wires, plugs, pcv, air filter, and coil pack. Any suggestions??? :confused:

I forgot to mention it gets worse with the A/C on graemlins/clonk.gif

The question is how fast does it shudder? Is it about once a second or more like a fast vibration of a few hundred a second?

If it shudders just a few times a second, It could be the torque converter lock up mechanism engaging and disengaging and needs a good mechanic to trace it down that has found the problem before and knows where to look.

If it shudders in overdrive above 45mph, and you shift it to drive, does it still shudder at that same speed range or go away completely. The lockup happens about 45 to 47 mph.

If the shuddering stays at that same speed range it is possibly a CV joint. You can push and pull on the CV joints as you slowly rotate each of the front tires. If you find a joint that is bad it will allow the axle to slide up or down and cause the tire to bind in rotation when it does this- causing the shudder. You need to have a hydraulic jack to jack each of the front wheels up one at a time close to the wheel to keep the CV angle near what it is with the car weight on it. Make sure you use a jack stand as well in case the jack slips.

If it goes away after shifting out of overdrive into drive at 45 to 55, it is possibly the lockup in the torque converter. Just drive it in drive instead of overdrive till you find someone to fix it. You will only loose about 2 mpg.

Or if it moves to a slower car speed in a lower gear it is still possibly a bad coil or spark module--did you check that your are getting spark at all 6 plugs after changing all those parts? With the engine off, pull one plug wire from a spark plug and stick an old plug in the wire and ground it to the engine.-- Start the car or have a friend crank the engine, and see if you get spark.

Shut the engine down and do this on one wire from the next coil and repeat this with one wire from the third coil. If you find no spark or weak spark from one coil, next try the wire on the other side of the coil to see if it is the coil.

I can "hear" many V6's running on 4 cyllinders, they sound different, every third cyllinder does not fire. You do not notice it in the car until the torque converter locks up above 45 mph. The engine really slows down when the converter locks and the engine slows way down to about 1500 rpm. The missing on 2 cyllinders is not noticed at higher rpm's above 55.

You said you changed the coil pack but not the ignition module under it. If you find that you have a dead coil (neither plug wire will fire the spark plug) with the new coil pack and you re-install the old coil pack and find that same coil is not functioning, then it is the spark module under it.

The old coil pack could have taken out the spark module so use the new coil pack on the new module.

The resistance across each coil tower is 12,000 ohms to 15,000 ohms.

The resistance across the coil primaries is about .3 ohms, that is a third of an ohm if you are wanting to check your old coil pack. I would check both.

Let me know what you find.

Thanks for the info I went through all the tests you described but what I found after doing a fuel pressure test and removing the fuel rail is that the number 2 cylinder injecter was not working. I cleaned it best i could and put it back together. Seems to be running fine now I am going to have the fuel injection system cleaned next, cause i still have a slight hesitation. Thanks for the help!