Okay here's the situation:
1996 LR Disco SE7

At about 45 or 50 mph my engine shudders. Watching the RPM's it will jump down from 2500 to just over 1500 and then back. It'll do this in a perfect rhythm. Back and forth. Over and over. The truck will maintain speed. In fact, I can even speed up... sort of. I didn't really push it. It's happened twice. The first time I limped it home and didn't drive it for a while. (I had to replace the rad. That's another story) The second time I got frustrated and pushed the gas. The engine shuddered as if it wasn't getting fuel and then bumped itself back into action and came on down the road completly normal. What is the deal?

It really don't feel like the tranny, which was my first instinct. The dealer threw me a few bones such as vacuum, misfire, and fuel problems but I'm not sure.

I literally just bought this thing. It's my first LR and I love it to death. I'm not afraid to do some work on it, but I want to be pointed in a reliable direction. Can anyone help me out? Please?!!?
Thanks!

Daryl Reid
Augusta Aviation, Inc.
Augusta GA

 

So have you had any check engine lights yet if so what codes?
The first thing that comes to mind would be the alternator, it drives the tach and if it isn't putting out enough voltage also it could effect the ECU and how it manages the engine.
Mike

 

That's a negative on the check engine light. Nothing except the Anti-Lock light is on. I've been planning on checking on that but I really doubt that it's related.

Alternator, huh? And excuse me for flaunting my ignorance, but by ECU are you refering to the computer?

 

YUP!!

 

So. Assuming that the computer is fine and the alternator is also good (considering there is no Check Engine light popping on), what would be next up the line to look at? Best educated guesses, folks, I'll take whatcha got! Thanx.

 

Maybe you should check the codes anyway, you should be getting something. If you just got the truck maybe the bulb conveniently quit working or disappeared. I had similar symptoms and it turned out to be a sticky valve, but I got the characteristic codes, over and over after a few resets of the check engine light. With my truck, it would feel like driving over railroad ties at 50-55 and lose power. I replaced the vehicle speed sensor (VSS) because that was suggested, but no luck - that's fairly easy.

 

Just out of curiosity, when you first start you truck, does your Check engine light come on and then extinguish? Bulb may be out and not showing...

 

Never assume, have your local auto parts store check the alternator to make sure.
Mike

 

Disco Guy: The light does come on and exstinguish normally during start up.

Mike: I'll have my alternator checked per your suggestion, however I've not seen any changes or irregularities in my trucks electronics (ie. headlights, panel lights, etc.).

 

yes it should come on and then go out.

When you see the RPM's going up and down, cane you hear the engine tracking the same, or is the tach just off? An erratic tach could mean abad alternator.