I have a 2000 Grand Marquis HPP with 108k miles. I’ve had some issues with it lately.
First, when I’m cruising at around 30-40 mph it shudders, but going at 45 and up it doesn’t shudder at all. Also, lately I’ve heard a slight ticking noise from the lower back of the engine. I don’t hear it on the inside. It’s barely noticeable. I hope you guys can help me. Thanks.
Your Transmission will shift into overdrive and lock the torque converter around 35mph. If your fluid is dirty and the filter is clogged, you can loose pressure and can get a shutter. Overdrive is affected first (normally). I would drop the transmission pan, replace the filter and dirty fluid in the pan. Depending the condition of the fluid (if it is burnt) you may also want to drain the torque converter.
If that does not fix it, your torque converter is probably going out. They have some weird friction sticks that can be added to the fluid that can help, but will not last. First try changing the transmission filter and fluid. I always use Castrol TransMax Mercon V.
For the ticking, it may be an exhaust manifold leak. Spray some soapy water around the manifold when it is cold and see if it blows bubbles. Probably won't do it long, so it may help if you have someone else start the car.
