Hello you Rover Super-Geniuses,

I've been searching around in the threads looking for an answer to my Disco's peculiar behavior. It has developed a tendency to "lose power" while under way. It feels as though it loses fuel pressure or spark. It does this in a rhythmic pulsing manner in about a one to two second interval. The RPMs will drop from say 2000 to 1500 and then bounce back up rhythmically. Sometimes it does this for just a few seconds, and sometimes it goes on for 10 minutes. At the worst times, the speedometer will flick back and forth wildly and occasionally it will go dead and stay that way until I restart the engine. Twice now it has caused the yellow check engine light to flash. (I didn't even know it could do that...)

It never seems to do this standing still, only rolling. And it seems to be more frequent at freeway speeds and when its hot outside.

I keep getting codes 1158 & 1313. (I've had that O2 sensor replaced and it didn't help at all.)
Having read thorough similar threads, I'm suspecting the VSS and / or the IACV.

I've got new plugs, a relatively new fuel pump (2 yrs), the 8mm Magnacore wires, K&N air filter & a new alternator.
I've been running Seafoam in the fuel pretty regularly lately. I usually fuel up with 92 octane.

96 Disco, 4.0 Bosch, 180k, lifted & re-geared

The VSS and IACV seem pretty easy and cheap, but troubleshooting mechanics is not my specialty. Does it sound like I'm on the right track?

Thanks in advance,
Chris

 

The VSS sounds like your on the right track, it's the only thing that's gonna bounce the speedo. On the flip side there was an issue with early 96 4.0 intake valves sticking due to the initial stem profile. I doubt that is it but thought I'd mention it. That would make the engine mis or stumble. Also.... just so ya know and not to embarrass the D1 and early P38's are GEMS (Sagem w/Lucas injectors) and not Botched fuel injection.......neither are worth bragging about...... unless you direct inject it.

 

Thanks ihscouts!

I'll start with the VSS and go from there. I actually found one on Amazon with the same part number as the AB unit for a fraction of the cost.

And yes, It seems I brain-farted and its the GEMS.

Best,
Chris

 

possible cracked coil pack?
does it do it in the morn when its misty or moist?

 

Nope. It really never does it cold. It really likes giving me the business after I've gotten on the freeway and gotten it up to 60+.

More often on the way home than on the way in to work.

 

Two thoughts....
1. the P1313 is "Catalyst Damage Bank A Misfire Fault"... so your cat may be on its way out.

2. If the trouble happens at speeds generally above 50 mph I'd say it is your VSS. When they go bad they sometimes send bad data to the ECU which thinks the car is traveling at a speed more than 120mph and shuts down part of the ignition system to protect the engine. I've been there.

You could try to re-build yours. Depending on its condition it may be better than the reasonably price aftermarket VSS's out there. The aftermarkets units are kinds junky but they do work.

Also, to get to the hex bolt on the which holds the VSS to the xfer case you'll need a LONG 4mm (IIRC, could be another size) hex driver. The longer the better because there are a couple of things in the way which will prevent you from getting the body of the socket close tot he head of the hex bolt on the VSS.

 

whoa now........ "ECU which thinks the car is traveling at a speed more than 120mph and shuts down part of the ignition system to protect the engine. 'I've been there'" - you've been there,..... I can only get mine up to 106mph! hahaha

yeah if no issue when moist or cold coils shouldnt be the issue

 

Ha....what I meant is that my VSS has acted in this manner. The elevated MPH interpretation actually shows up on a real time OBD reader.

Here is how I came about diagnosing it in my truck. The top reading on the video is coolant temp, the bottom is the MPH from the ECU.

https://landroverforums.com/forum/di...eed-ecu-79498/