My 98 200K miles started cutting off and on, like it would lose power for a second or so then back to normal for a few seconds. It cranks fine, I drive it for for about 15 miles and it starts this cutting out. Funny thing is it started this about 3 years ago, only once in a while. After a month or so it stopped. Then it started up this up again a few months back. ( I don't drive it that much, once a week at most to town). My son had it and it went dead on him at a stop light. That turned out to be a few pump. Changed the filter as well. I figured problemed solved. Then it came back after a few trips to town. It always after at least 15 miles or so driving. Changed plugs and plug wires. Autozone said I was getting misfires on 5 & 7. (did not get the codes from him). I was told it could be a coil pack. Cylinder 5 is on a different coil than 7. I swapped coils 2 & 3 with 1 & 4. Hoping the trouble moves. I went to Advance Auto this time and had them to erase all my codes. I know I need to go back and have a reading again to see if the troubled moved. (Might as well buy an OBD reader). From other threads similar I've read it could be anything, from plugs to blown head gaskets to slipped sleeves. Seems this would act up more ofter if a gaskets etc. The vehicle is warmed up here good in Florida after a few miles. There's no water loss nor smoke out the exhaust. Sometimes it starts running ok after a few miles of this cutting out. It does it in Nuetral also standing still, the tach will fall back then jump back up. Any ideads or do I need to get the codes first? Oh, I just had to replace my worn out water pump this month and alternator last month and of course the fuel pump just before that. But that's the first time for all that.
Thanks guys.

John

 

Speed Sensor / Transducer - Vehicle - Road - Vss | Land Rover Electrical Parts, Batteries, Relays, Lamps & More

Problem solved.
It is also the speed limiter for the truck, when it thinks you are going to fast it kills spark to the engine one cylinder at a time to slow you down.
When it goes bad it kills spark at random and for no rhyme or reason.

 

Thanks Spike. $174 is a lot of money, but if it makes this go away it will be really be worth it and it could be worse. I read something that it can cause the Cruise Control not to function, you hear of that? I was just trying my cruise control yesterday for the heck of it to see if the Disco acted the same under that, and the cruise control would not work.
The VSS is on the transfer case???

Thanks again

 

Yes the VSS is on the t-case, there is a write up on how to replace it in the tech section of discoweb.org --.
If you shop around you can get it cheaper than at AtlanticBritish, check e-bay and Google.

 

will do and I'll post my results. Thanks

 

Before you swap try pulling it out, cleaning, greasing and putting back in. This is according to disco mike. I've already checked around to see if anyone had a dead one I could dissect but nada. Also couldn't find any on eBay. Looks like though on d-web, if it doesn't spin freely or is rough, it's shot.

 

Thanks. I tried to Google and looked at Ebay and Amazon, nothing. I'll try what you suggest first. Something else I wonder but haven't tried, will it run with the VSS unplugged, meaning if I unplug the wiring connector from it?

 

Yes you can unplug the VSS and drive, your speedo will not work but this is a good way to verify that the VSS is bad.
Sorry I did not mention this test before.

 

I'm going to assume no as the vss talks to the ecu and the ecu is making constant adjustments. But someone else may want to chime in.

Well there you go, Spike is much smarter than most.

 

The GEMS will adjust for the lack of a signal from the VSS and estimate that value.