Land Rover Repair: Engine Misfire, engine misfire, coil pack

Question
I own a 96 Disco SE @ 97000 Miles (Manual)
When driving uphill in 4th or 5th gear at 55MPH at approx 3000 rpm I feel a rough vibration from the engine and loss of power, when easing of accelerator it will go away but will drive slower or have to down shift. Instead when accelerating more, check engine light will come on. LR text book diagnosis found misfiring in multiple cylinders, and they mentioned I need a new Coil pack @ $650+. Why would this only be on a hill and not when just accelerating fast.  

Answer
Hi Alex,

interesting question.  I suspect the added load of the transmission (drag + speed) is compounding the coil faults.  

Depends also on the grade of that hill.  In my Disco,  my RPM would be around 2100 at 55mph (5th gear).  Downgearing to 4th would increase the RPM and the engine would be firing faster.  IF there is a problem in the coil, not enough spark is being provided.

Have you had your spark amplifier module tested?  I've heard that with SAM failure, loss of power and misfiring can happen.

Have you checked out the internet for a replacement coil pack?  http://www.car-part.com/

I've seen a '96 coil for as low as $68US.

IF that is your problem.

Best of luck,

JohnMc