Caanon

Edit:So I skimmed your post a bit too quick and missed some stuff about why you're parting out...I'll just leave this like this for the information it has. Basically how the ignition works is as follows: The ECU takes info from the engine speed sensor and cam position sensors and decides when a spark needs to happen. It sends a signal to one of the two ignitors(there are two, but they are in the same small box) the ignitor the sends power to the coil and then coil sends power into the distributor on one side of the engine through the center of the 5 wires. The distributor then sends power to the spark plugs. Even though there is a left and right distributor I think each one sends power to plugs on both sides of the engine, it is not that one side only does that side, it is split up. This is what the coils look like http://www.carsteeri.../CUF72-Map1.jpg You can see one here, right by where the coolant goes into the engine: http://lextreme.com/...e-SC400 013.jpg The other one is on the drivers side below the cam/distributor cover(not inside, but nearby) You can test which side is not giving spark by unplugging the center wires going to the distributors and seeing which sparks to ground. I haven't done this next part, but saw it recommended in my research, remove and switch the coils and if the sparking reverses you know that not working coil is for sure the problem. If the problem stays on the same side it is either the ingnitor or the wiring somewhere between Ignitor ->coil -> Distributor.. You've already switched out ECUs so it's not that. I think if it was the ECU you would have no spark at all which is my problem. I definitely not an expert, but I've spent a lot of time figuring all this out recently. So I skimmed your post a bit to quick and missed some stuff...I'll just leave this like this for the information it has.

It is probably the Ignition coil for the passenger side, or the ignitor. I'm pretty certain you can swap the coils and if the problem reverses to not firing in drivers side it is the coil, if no change than that would point to the ignitor. I've learned a lot about the ignition system in the last month, my problem was no spark at all due to a faulty ECU. I think a coil or ignitor are each around $50, but not sure.

What happened with mine is that the wire broke. I guess from opening and closing for 12 years. Open up the black plastic sleeve by the right side hinge and check if the wire is in one piece.

If a search here doesn't work to find any info, you can try searching first, then asking at clublexus http://www.clublexus.com/forums/forumdisplay.php?forumid=6 Quite a few people there have changed to 95+ LS400 brakes.