LS400 rough at idle & Hi rpm

[LSKid]

Hey guys, i have an annoying problem.

Its a 91 LS400 240000km's. Problem is at idle once running for a while its has a slight miss. At hi (4000rpm +) under load it misses/splutters badly when you nail it from about 2000 rpm.

So far I have replaced the plugs, fuel filter & checked all the leads, also fuel pressure regulator. I've checked the intake and all ok.

In Park or Neutral you can take it up & down the rev range no problem. It's only when its under load.

A good mate that works on them has suggested either the fuel pump or a coil is starting to break down.

Any ideas. I can still drive the car if I take it easy at the moment.

 

[sideshow]

could still be the leads
fit a spark tester on each lead one at a time
make sure gap is set to about 20 to 30 mm
then crank engine each time on each lead
each cylinder should be able to jump the big gap
if u find one cyliner which cannot jump the gap then thats yr faulty lead
this tests the ignition system under big loads when u have a big gap

 

[LSKid]

I have tried with the engine running un plugging each lead separately & hearing for a difference in engine idle. Each lead made it drop down.

So this should indicate all the leads are good from memory. Also theyre about 50,000km's old Kingsborne with about 1.9-2.6k ohms resistance same as when they were new.