Jeep Commander Forum banner
1 - 3 of 3 Posts

·
Registered
Joined
·
30 Posts
Discussion Starter · #1 ·
This is on a 5.7 hemi.

Previous Jeeps I've had, were manual transmissions with the tach. This is the first automatic transmission with a tach I've ever driven.

No problem during accelleration. I see the RPMs increase, when I feel the transmission shift, the RPMs go down, and start increasing again. No problem. Normal.

But sometimes, when I'm on fairly flat roads (30 - 40 MPH range), the RPMs will suddenly decrease from 1,500 to 2,000 range, down to 1,000 and sometimes to 500 RPMs. To catch the engine RPMs suddenly decreasing, without any apparent reason (like shifting up) or speed decrease, causes me some concern.

Is this normal? Is this something like the transmission disengaging?

If after I get up to speed, and I let my foot off the gas, the RPMs seem to stay constent. It seems that it only happens when I still have my foot on the gas, but in the way you would do to keep a consent speed. Then the RPMs falls.

When this happens and I do give it some more gas, there is a lag time before I notice the RPMs increasing and then the increase in speed.

This is not on cruise control.

Is this "one of those" problems that will hit me later or perhaps, a gas saving feature?

After having the engine braking of my old Jeeps, it seems that when I come to a red light, my Jeep speeds up. I know it doesn't, it is just I expect engine braking at that point.

Anyway, I bought it in January and have 1,200 miles on it.

Thanks

Tom
 

·
Registered
Joined
·
8 Posts
Sounds like the MDS engaging. With the Hemi the computer tells the engine to shut down 4 cylinders and reduce the revs for low-load situations (like when you're doing 40 to 45 mph) on a level road. Enjoy it. You're saving gas!!
 

·
Registered
Joined
·
195 Posts
Comment on the braking. I had 3 Cherokees, all with sticks. Now, the JC 4.7 with its auto. I find myself running in the city mostly in 4th, downshifting to 3rd on braking. (Mileage 17-18.) Habits maintained with the auto.
 
1 - 3 of 3 Posts
Top