When you say you "pulled" the relay, do you mean you swapped it or did you do a test run without it? (I'm not sure if that's even possible though)

 

I would pull each relay one at a time and ensure both pumps were working, also check pressure at the rail for each pump. If pressure is good then I'd say the pumps were not the cause of the problem.

 

Sorry....what I meant was that I took each relay out in turn then started the car and revved it while stationary.


Its strange as on a short run it behaves but on a longer one this develops....as if something is breaking down after 20 minutes or so use.


I've got to get hold of a pressure gauge to do that next.

 

At first it sounded like water getting into your spark plug wells, but since it is after warmup the miss fire starts, it could be the spark plug boots themselves leaking as the rubber sofens up. Not too hard to pull them to check see, and maybe tape them up for a quick test to prove this. (I don't know if you could slip garden hose or something similiar in there or not as a test) The missfire mine had was IF I parked it outside and it rained in thru the louvers. I got out my vaseline and greased up the coil cover plate gasket and it's been running fine a couple years now. Lack of fuel miss fires usually occur only under high load or speed conditions.

 

Looking trough the history file it seems that this has been an on / off fault for some time.


the first 'fix' was water in the plug wells and the covers seem to be sealed with mastic.


The dealer I bought her from 'fixed' an intermittent misfire with a new fuel filter.


He said the way they diagnosed a fuel pressure problem was by installing a pressure gauge and taping it to the windscreen while driving it hard.


I'm assuming I have the same problem still so think I'll take it to my local rolling road and get them to do a test run.