Land Rover Repair: Intermittent loss of power on 98 auto Disco, throttle position sensor, green paste

Question
Hello John,

My 1998 Discovery 1115,000 miles, runs fine around town, but on a long run the power comes in regular spurts, 5 seconds full power, 5 seconds about 1000 RPM less and so it goes on. Really frustrating. After 50 km the problem will stop and reoccur a bit later. Happens at all speeds and is particularly bad when the motor is under load proceeding uphill or overtaking. I have replaced the fuel filter. A road side mechanic (I live in Turkey) diagnosed water in the fuel tank, but that seems unlikely. Any thoughts?

Thanks for the great service,

Sean Crowley  

Answer
Hello Sean,

Your '98 Disco may be having troubles with the TPS (throttle position sensor), the timing chain is worn, or even the spark amplifier module.  

IF it was water, you'd have the problem when you tank becomes low on fuel.   Water is heavier and settles on the bottom.  Purchase a paste that changes colour when dipped into fuel tainted with water.  The one I know of is a green paste that turns red when water is detected.  Most service stations use this method of monitoring water levels in the fuel reservoirs.  Should be the same in Turkey.  Ask to use a small amount to detect water.

Is that 1,115,000 miles on your Disco or 115,000 miles?  I have 170,000 miles on my '95 Disco.  TPS was changed along with the spark amplifier to solve my rough idle and power loss.  RPM should be at least 750 at idle, revs above 1000 may also indicate ECU problem ( I hope not! $3000US)  I'd replace the TPS first as it is only about $80US.

Only you know how well you've maintained your Disco.  You could try new spark plugs and wires if they have not been changed for awhile.

Best of luck,

JohnMc