Liybzd

Hello, today my 96 ls400 started to run really rough on a lunch break, the CEL flashes from time to time, I found 5 codes: P0300, P0302, P0304, P0306 and P0308. So apparently it misfiring on one bank, I doubt if it's related to individual spark plug or the coil, please help diagnosing, it's the first time that it happens.

Note: I noticed it got really rough while idling and smoother when driving, probably fuel pressure regulator?

Update 8/24:
The problem went away after I replaced the caps, but it came back today, it was quite brief and the car ran smooth again after 5mins, I read the code and they’re p0300, p0306 and p0308, two cylinders on bank 2 misfired.
I erased the code and drove for another 10mins, it didn’t come back. Any idea what could be the issue? I plan to start from spark plugs

mckruzer

Have you had the ECU caps changed yet? I was having misfires also. Codes 300,302,303,304,305,306,308. I changed both coils, wires and plugs with no results. Then i had my caps changed and it solved all my issues.

Liybzd

No, I haven't, is there a way that I can open up the ECU and check?

mckruzer

Yes. Refer to Cowboys link. I also have the 96 ls400. I took it to an electronics shop and he was able to fix the copper tracks and check all caps and resistors to make sure they were up to par. It fixed all my issues.

https://www.clublexus.com/forums/ls-...capacitor.html

YODAONE

After 23 years the capacitors are tired...and if they start leaking can damage or destroy the circuit board.

Go to the ECU capacitor link in this forum, order the correct parts specified in the post, and find a qualified electronics repair shop to extract old capacitors and install new.

mckruzer

The circuit board copper tracks can be repaired by a qualified tech. Mine was.

Liybzd

Thanks for your suggestion, just bought the capacity pack on eBay. Looking through the symptom list, my car had a few issues intermittently in the past: the speedo didn't work after starting up the car and suddenly back to life after a few minutes driving; the cranking is not consistent, some times took a second and sometimes can be 3 or 4 seconds; and of course the smell of the exhaust today is very bad, as if I ran straight pipe.

mckruzer

Im not a pro at this. But from reading Cowboys post theres all kinds of strange intermittent issues due to a bad ecu and sounds like your experiencing the same weird stuff. My thought process was that if the rebuilt ecu didnt fix my main issue, it would fix another that I wasnt aware of.

oldskewel

iTrader: (1)

Hopefully you got the good quality / specs on the eBay capacitors. Should be clearly listed in the capacitors thread.

I did the job myself on my '91 pre-emptively, figuring if it was a known defect, and it would be needed one day if not now, it would be better to swap them out before they leaked and caused further damage.

So I was slightly surprised when it seemed that a few weird minor problems got fixed by doing this ... things I did not even know were problems, but they were, and they got fixed.

I'm sure if someone were to look at my ECU board, it would be clear that the caps had been swapped out. Yours may be similar - the new caps and solder will just look different enough from everything else that you will know if it has been repaired or not.

Liybzd

Status update, had my caps replaced yesterday and misfire went away. From just the appearance, I had 3 out of 6 caps leaking. Thanks all for your suggestions

jaaa

thanks for coming back and posting results.

RA40

iTrader: (6)

Glad that resolved the issues. Getting the caps replaced is one of the top areas to check with these year LS's.