Two months ago my disco developed an occasional intermittent misfire on cylinder 4 that slowly got worse over the course of a week. I pulled the old spark plug and replaced it with a new one and the issue went away for about 20 miles, then came back slowly again. It would miss usually only while climbing hills and when bogging down the engine. Upon further inspection, I realized that the cyl 4 plug wire had a bad burn spot and I decided to replace it. This fixed my issue for about a week and then the misfire slowly came back but this time is on cyl 6 and 2. As time went on, the miss became worse and now it misfires about 50% of the time rough and smooth switching back and forth every few seconds. Next, I decided to change all of my wires, plugs, as well as my coil pack assembly but the issue still remains.

I am planning to do a compression test soon just to be safe, but besides a blown head gasket, what else could the problem be? Possibly injectors? Please let me know what you all think.

 

I'd pull the upper manifold and check injector wiring harness...and injectors. The wires going to the injectors are bent over pretty good, at the top of the unjector, and the wires looked really brittle on mine (but we're okay). However, i've read of folks having issues with the wires. Also, replace the o-rings on your injectors while you're in there...or replace/rebuild them also. If you are seeing misfires, me...l'd just replace them.

Brian.

 

You can use a cheap USB boroscope/endoscope hooked to your phone to look inside the cylinders for signs of coolant. That would point to either a failed HG or failed block.