Not usually one for resurrecting old dead threads but..... Finally got to the bottom of this one, and whoever said VSS gets a gold star. I had not experienced this problem for about the past five or six months, and for whatever reason it did it to me this morning on the way into work, and I happened to be staring at my ultra gauge at just the right moment finally and noticed that when this event occurred, I had exceeded escape velocity and was traveling at 186 mph. Even though it still felt like 70. The sputtering and skipping stopped when the speed locked back in and read correctly. Has anyone had any luck with the VSS rebuild procedure, or know of a cost-effective source for a replacement part, those darn little things are pretty pricey

 

I ended up getting a VSS from bputah.com, the $105 aftermarket one. Too many posts said VSS consistent with intermittent loss of speedometer that I also experienced (my earlier post reported success with fuel cleaner during a trip where I experienced the intermittent power loss). Replaced it last week, then went on long trip with no speedo/power loss issues (had brake lockup problems, but that is a separate post that I will comment on once me and my mechanic figure that out).

It was easier getting to the 5mm hex head bolt when sliding under the vehicle from the passenger side to position arm/hand to access the bolt (I was at it for an hour going from driver side and could not get good hand/arm position, went quickly once I changed positions). There was space above a heat shield for my right arm to go to get my hand into position. Take a flashlight or shop light under with you as the bolt is at the top and it is a tad dark up there. Also, the electrical connector has a little locking tab so take a small flat blade screwdriver to pry that up a little to disengage.

When you remove the VSS, look up into the hole and you will see a small square tube; the pin on the VSS goes into this tube so make sure you line up the VSS pin and get it into this tube as you replace the VSS (this is critical but the pin and tube appear to be self aligning making it a little easier, I just happened to see it and I don't recall anyone mentioning this). It was easier for me to also have the bolt in place in the VSS and use the allen wrench engaged into the bolt to help position the VSS. Be sure to use some thread lock on the bolt. Once VSS is in place, I used a finger from left hand to hold it in place while I tried to engage the bolt into its threads (took me a few tries, worth looking up when you check the tube to also get an idea of where the bolt hole is as it is not straight up from the tube).

When I was reconnecting the wire harness, it would not quite engage the locking tab. Turned out the harness was getting caught on something preventing it from moving just far enough to engage the lock, so make sure the harness is moving freely before you reconnect it. There is a little half circle tab that the wire harness goes into to hold it in place once you reconnect the connector.

If the speedo does not work when you test drive, my guess would be that you did not get the VSS pin engaged into the tube. It looked to me that it was possible to do this as the pin on the VSS has a fair amount of slop in its movement. Everything worked first try for me. Good luck!

 

Thanks for the writeup, looks like I need to tend to it sooner rather than later. Was hoping to let it slide for another six months but it skipped on me again today, this time tho the ug only said I was going 141. Interestingly, the speedo has never flinched. Must be some filtering going on there.

 

Dicovery 90K - 2nd engine rebuild.

Intermittent momentary loss of power while driving.

speedo and dash lights bouncing and flashing then back to normal.
noise on stereo when using elctrics, windows, gas sometimes?

what is VSS and ECU?
First time using the forum am at the end of my tether with this issue.
getting dangeruos when car stalls on slowing down at lights and no brakes of power steering, just tons on metal with little control.....

Appreaciate any help,

Thanks,

Gary

 

VSS is Vehicle Speed Sensor that is attached to the transmission. ECU is Electronic Control Unit, there are several of them (do your rear windows still work? no? that's the window ECU) but the main one, called the Electronic Control Module (ECM), controls engine activity, gauges, etc. According to the service manual, the VSS is for determining road speed for the electronic speedometer, cruise control, and the idle air control. As noted in this thread, a faulty VSS will report a high speed (like 150mph when you are doing 70) causing the ECM to reduce speed like a governor so it feels like you let off the gas when you did not. My experience is that the speedometer temporarily goes crazy and I recall getting some radio static at the same time. Just found this helpful phrase in the service manual, "Should the vehicle speed sensor fail in service the ECM idle air control would become erratic."

Stalling when slowing down, causing loss of braking and power steering, may be a separate issue. I have not had that problem yet (knock on wood). Loss of power steering and vacuum assist on the brakes seems to indicate that the engine died. Did you have to restart the engine? Is the vacuum line that goes from the brake assist to the valve cover rotted and intermittently causing a vacuum leak?

Replacing the VSS might be a good way to start. As someone noted above, there is a repair thread in this forum somewhere and my last post above details what I did. I have had no speed and speedometer issues since replacing it.

Good Luck!

 

LR Discovery 1 2500 TDI 1993. Located in Tanzania, East Africa
Cruising nicely at just over 100 kmh when hit by sudden loss of power and huge clouds of black smoke. Pulled off the highway and checked under the hood - nothing amiss to see. Engine would idle fine but not rev beyond about 1500 rpm. Not overheating.
Needed to be towed home however today the car runs fine.
What do I look at first?

 

Not a diesel guy, but a quick internet search says EGR valve failure gets you smoke and loss of power. Do a search on "discovery tdi egr" and you will get several hits, most of them on removing it interestingly enough. Might be able to clean it and get by for a while. Happy wrenching!

 

Thanks for your thoughts. Mine must be one of the very early Disco 1 models as it is not fitted with EGR. I am no fan of this technology so am relieved to see that it is not there.
Now I am thinking that the wastegate must have jammed open and then later returned to normal function.