rcftx68

1993 Lexus SC 400 stock
Since I hve been anticipating my poor running to worn capacitors in my ECU, I went and purchased a use ECU from a junk yard this morning. model 89661-24230 the exact same as my original. I took off the covers to inspect the board and sure enough a few of the capacitors are leaking. The leaking has not been sufficient enough to destroy the board and with new capacitors I should be able to revive it....But just for fun I installed it to see what the car would do. After installing it...I let it initialize once I reconnected the negative cable to the battery and then let it sit with the ignition key on start for a few minutes. Once I to start it...it started immediately, however as soon as I take it out of Park and put it into gear it immediately shut the engine down?....So i am wondering what gives??? Anyone know? Could it be the two capacitors that are leaking or is the ECU not properly initialized with my particular SC400? Again it is the exact same model ECU as my original....It should be a plug and play correct???

Thanks for your thoughts,

RCFTX68

Yamae

What I assume is that the ECU from a junk yard was already partially dead or you damaged it. Did you pay enough attentions on the ESD and countermeasured it using a wrist strap while or something similar doing the job?

Without re-writing any data, another 93 ECU should work as long as the part number is the same and not damaged.

Incidentally why did you use an IS forum to post a SC400 related question?

rcftx68

Hello and thanks for the response. I am sorry if I mistakenly posted this question under the wrong format within the club lexus forum. Anyway, relative to the ECU I acquired I did very carefully open the ECU without disturbing anything to view the Capacitors and noticed two were in fact leaking slightly. Other than that I did not do anything to it since I am waiting for the capacitors I ordered from DIGIKEY to arrive at the end of the week. I was just curious that the engine with this ECU installed would allow the engine to start normally but as soon as I put it into gear ..it would immediately shut everything down! Could just two mildly leaking capacitors do that??? and if apparently so hopefully the correct and new low esr, high temp resistent long life capacitors researched by LScowboyLS and approved by you should correct the problem. I was uncertain since I saw videos on Utube about swapping modules out of an original non working or damaged ECU to allow a new ECU to initialize with the vehicle. Apparently as you have indicated that is NOT necessary with an early Lexus as in the 1993 Lexus SC400. Therefore, other than fixing any potential damage on the board ....once repaired all I would need to do is just plug it in and let it reinitialize with the key on start for a few minutes and then with the ignition turned on it should be good to go.....Am I correct making that assumption?

Thank you for your expert advice...

Regards,
rcftx68

Yamae

I don't know that I should write the answer here or not since this is an IS related forum. But anyway I answer you here.

>Could just two mildly leaking capacitors do that?

Yes, any minor leak means that the capacitor is completely dead. Even no leak is already nearly dead and not working properly as long as it is aged. A 93 is aged enough.

You need to know that those QAS capacitors become not in good conditions any more when aged even before the leakage starts. The pH level inside becomes too high and the capacitor can't work well and finally the legs are corroded due to the too strong alkali level inside and the leak-out starts. At this stage the car doesn't run well but also traces around are damaged. So the minor leak is already too late as you can see the photo at the page below.
https://www.clublexus.com/forums/ls-...capacitor.html

Unfortunately many Toyota/Lexus high-end cars in the final decade of the last Century have QAS capacitors inside of the ECU. Those ECUs have to deal with many processing jobs and need good DC supplies even at very cold conditions. For this purpose, QAS capacitors were introduced to remove the ripple well and those had been working good for a decade + α. But those seldom work well for 2 decades according to my experiments + experience. That's why I suggest people to replace those capacitors as a PM.

The capacitor thread above is now too huge to read thorough but you will be finding many happy LS400 and other Lexus cars owners who have replaced those QAS capacitors as a PM although they never had noticed any leakage. Some say, "Runs like new" or "Never noticed that the car runs that better".

Hope your project will be going well.