By Scott A. Keen (Scottkeen) on Tuesday, July 24, 2001 - 08:01 pm: Edit

I had been heading back 350 miles on I-95 this past weekend. During much of the stretch of highway, I noticed that the Disco was "lurching" intermittently every few minutes, when I maintained speed at 75 mph.

I tried switching off the A/C to see if the compressor was kicking in and putting load on the engine. Nope, still lurches.

I also tried it both with and without cruise control. Same problem.

If I slowed down to say, 70 mph, the lurching stops.

My friend who was with me says it's probably because I'm just at some RPMs where the transmission is switching between gears.

Anyone know what this lurching is all about?

By Alex Schubow (Alex) on Wednesday, July 25, 2001 - 01:07 am: Edit

Sounds like a defective vehicle speed sensor.

Alex

By AntonyK on Wednesday, July 25, 2001 - 02:17 am: Edit

Also try the Throttle Position Sensor on the Plenum Chamber.

My 1997 did a similar thing and it's not happened since.

By Scott A. Keen (Scottkeen) on Wednesday, July 25, 2001 - 03:21 am: Edit

Can you guys tell me where to find these components on the vehicle?

btw, this is a 1997 SD

Scott

By Daniel on Wednesday, July 25, 2001 - 05:02 am: Edit

Scott,
Please post the results of your work here. I am having a similar problem, although I can only barely detect a very slight lurching at highway speeds.
Thanks,
Daniel

By Jay R. on Wednesday, July 25, 2001 - 06:34 am: Edit

What exactly is "lurching" ?

I had a similar problem with my 97 Disco. It would feel as if the engine is cutting in and out. The rig would loose power for a moment and then regain it.

If these are symptoms, I would recommend checking the vehicle speed sensor (or replacing it). After the VSS was replaced on my rig, I have never had this problem. Seems to be a pretty common occurence.

HTH,
Jay R.

By Alex Schubow (Alex) on Wednesday, July 25, 2001 - 11:52 am: Edit

The speed sensor is mounted on the transfer case, on the driver's side of the vehicle, behind the brake drum. Kinda tight in there, but you should be able to squeeze a ball-end 5mm (I think) allen key in there to remove it.

Alex

By jec on Wednesday, July 25, 2001 - 06:30 pm: Edit

The lurching was also the first sign of sticking exhaust valves on our 95. We'd notice it only at highway speeds or when the truck was pulling hard up a hill.

By Daniel on Thursday, July 26, 2001 - 05:36 am: Edit

Jay,
In my case, "lurching" is a slight loss of momentum. It feels sort-of like the truck is shifting gears, but it happens between 70-80 mph going a steady speed. It is very vague. My girlfriend, who is usually in the truck with me, says she doesn't feel it most of the time. Does this sound familiar?
Thanks for your input,
daniel

By Jay R. on Thursday, July 26, 2001 - 12:14 pm: Edit

Daniel,

Is the truck still under power when lurching ? Do you notice a loss of power ?

The problem with my truck was a loss of power for short periods of time (<= 1sec ?) at hwy speeds. It felt like the speed governer cutting out the engine power.

If what you are describing happens without any loss of power, it might be a different problem.

jec,

I was under the impression that sticky valves would trigger the check engine light. Is this not true ?

By jec on Thursday, July 26, 2001 - 07:07 pm: Edit

Jay:
They didn't trigger the light in our 95, and we certainly had a bad case of them. Don't know if they will trigger on an OBDII 96 and later. There is an engine misfire code, but I don't know what triggers it. Anyway, Scott's original post about thinking it was the A/C or cruise control was exactly what we were thinking. We'd be going along the highway at 70 with the cruise on, and every few seconds there was what felt like a momentary loss of power for a fraction of a second. Barely perceptible, but enough to tell you that all is not right with the Rover. Then we were going up a 15% grade at 9500 feet and the engine started sputtering and would barely pull the grade in first gear. Dealer pulled the heads, said several exhaust valves were badly carboned, rebuilt the heads with the new-style valve, and all has been fine (at least with that problem) since. Thank goodness for extended warranties!
John

By jec on Thursday, July 26, 2001 - 07:13 pm: Edit

Jay:
The engine misfire thread going on simultaneously started with a check engine light in a 96 being diagnosed as valves. So it sounds like it lights with OBDII.
John

By Daniel on Friday, July 27, 2001 - 04:32 am: Edit

Jay,
My truck (98 Disco) actually has a bit of a story to it.
But here it is as briefly as possible:
I bought it 1 1/2 months back w/68K and it started with a rough idle and check engine light shortly thereafter. I put in new plugs, wires(one wire came apart in my hand as I removed it) and air filter and the idle has smoothed out considerably but I don't think completely. But, the engine light has gone out by itself.
The only engine symptoms I am noticing now are this lurching, which is a very brief thing and not severe at all, almost like it is shifting, and a very low popping sound from down by my feet(I think). I think the latter has to do with the exhaust somehow. It does not coincide with the lurching. I was going to address that after dealing with the more pressing issue. Which is deciding whether the lurching is actually a problem or am I just paraniod.
I am driving a hundred or so miles this weekend. I will monitor it closely and see what happens.