Misfire

[JayBeeBee]

Ok, Im hoping some knowledgable person can help with a problem with my 2002 LS430 before I end up scrapping it.  Vehicle has an intermittent misfire and when it does, the EML comes on and it it runs on 6 cylinders. Did diagnostics and it said random misfire cylinder 5. Checked plugs which were a bit dirty so replace all 8. Cleared codes all was well for a few days, then came back. this time saying cylinder 8.  Was told possible coil pack so replaced it and again cleared codes all was well, came back this time cylinder 3 so replaced that coil pack and the rest of them. Again, all fine then came back as cylinder 5 again. was going to swap injector to see if was fault, put diagnostics on again, said cylinder 8.  Am at a loss... can anyone suggest what could cause misfire to swapped cylinders.  Sometimes the light flashed and it it runs lumpy, other times the light stays on but performance is normal.  Any help greatly appreciated!

[Malc]

if performance is " normal " then it's a bit too far to just scrap her !

if it really is " normal " then if an auto electrician can't fix it and if no one on here can suggest the answer ........... might i just think aloud that when she goes for the MOT that your indy mechanic dealing with the MOT ensures the " light " is reading normal at that moment in time and you live with it in between MOTs

Malc

[The-Acre]

Did you do your own diagnostic?  My wife had her car checked by two garages that came up with different possibilities, we then took it to a place (although more expensive) that had vastly superior equipment and immediately they diagnosed the problem.  That's what I think I'd be doing.

[JayBeeBee]

Was done using snap on diagnostic machine :(

[The-Acre]

24 minutes ago, JayBeeBee said:

Was done using snap on diagnostic machine 😞

I would still get it to a Toyota or Lexus dealer who will use Techstream. 

[steve2006]

Have to agree with Phil regarding the diagnostics by Lexus/Toyota as this should be able to see injector function and pulse times.

Does the fault appear temperature sensitive i.e. appears more when the engine is cold/hot or at any time?

The coils are earthed at 2 separate points so may be worth physically checking both are good and sound.

The crank sensor input can also affect plug firing if the signal is corrupt.

[JayBeeBee]

No seems to do it whenever it feels like it. Although i have noticed its not as frequent when driving along motorway and that it starts to run lumpy at idle speeds. 

[ColinBarber]

random misfires across multiple cylinders are normally caused by fuel rather than ignition (e.g. injector(s) not coil packs/plugs). The ECU is normally able to reliably detect which cylinder is at fault if the ignition is at fault.

Possibly a leaking injector, rather than an electrical issue.