Thats really good news Perry.Congrats on the fix.

Great news! Highly recommend getting that ECU rebuilt now before you run into the same issues down the road. Every one of them will have some form of cap leakage.

Except the one that I sent to you, right?

Not sure what the techs found specifically with yours. There was no major leakage all over the board. There could have been some starting under the caps or like you mentioned going bad internally, prior to leaking out.

I'm not sure, either, because I never got a straight answer from your staff except "it can't be fixed, but we'll sell you a replacement for $399".
But it couldn't be the caps - that's what you guys do, right?
You replace the caps, and the ECU works again. You've done it a hundred times.
But since your staff said it can't be fixed, it must have been something besides the caps.
So, as I said, the caps were fine, and, unlike what you said, not all of them have some form of cap leakage.

No, not entirely true. The caps can be bad and even leaking all over the board and an ECU will still "work" and a car will run without any visible issues, or have very slight noticeable issues such as a hiccuping idle.

If you open up your new ECU you will likely see some signs of cap failure if they haven't been serviced before.

perhaps an ECU problem?
 

i've read through many of the responses on this thread and tend to think my problem (crank-start for 1 sec and car shuts off) is associated with the ECU. even if its not, my car is an 1990 ls400 heavily modified and ECU was never touched. i should replace the capacitor even if my issue isn't caused by the ECU. for a car that has been in storage for 12 years (during that time, never started it once because i was overseas). i came back to find a lot of things basically falling apart. I've since then did a lot of tune up here and there and still it will only crank up but no start (sometimes i get lucky and it starts but for 1/4 of a second and shuts off). NOTE: it will only start if i spray starter fluid in the intake for however many seconds depending the amount of fluid i spray. if you have not seen my post in my attempt to try to resurrect this once "a show car" please take a look.. any advice you may have is appreciated.

https://www.clublexus.com/forums/ls-...-12-years.html

out of curiosity from all the information in this thread i read thru 100s of responses. today for the first time, i took out the ECU. it "appears" to be in very very good condition. given that the car only has 100k miles on it even though its almost 30 years old. i was looking for any thing out of the ordinary like capacitor leakage/damage traces and found none. however, i understand the fact that capacitor has a life cycle so i will probably take the chance to change it all out. i bought another ECU today just as an back up if i screw up... the P.N doesn't match my current one but its from a 1992 LS400 non TRAC so i think i am good. posting some pics here in case someone out there has an sharp eye and see some flaws that i dont see. either way, wanted to reach out because many folks here have had their success and i am just starting my journey (once again).

https://cimg2.ibsrv.net/gimg/www.clu...71b740ea77.jpg
this car has seen its better days.
https://cimg1.ibsrv.net/gimg/www.clu...3719dfc44b.jpg
https://cimg2.ibsrv.net/gimg/www.clu...93b2c6e9a5.jpg
https://cimg5.ibsrv.net/gimg/www.clu...cd2dd3a16d.jpg
https://cimg7.ibsrv.net/gimg/www.clu...92f40e3bd4.jpg
https://cimg8.ibsrv.net/gimg/www.clu...dfbc35bd5e.jpg
https://cimg9.ibsrv.net/gimg/www.clu...2bd348f0ab.jpg
https://cimg2.ibsrv.net/gimg/www.clu...592ec0d42d.jpg
https://cimg3.ibsrv.net/gimg/www.clu...2c113cee63.jpg
https://cimg4.ibsrv.net/gimg/www.clu...d1d47c5f41.jpg
https://cimg5.ibsrv.net/gimg/www.clu...e24ee8874f.jpg
https://cimg6.ibsrv.net/gimg/www.clu...fc06c14292.jpg

i changed out my capacitors as well on my 92 SC. It also had no visible leaks, but I've been told by other EE's that electrolytic capacitors have a shelf life of 10 years, so they're overdue for changing, and wound up replacing them. I noticed my car ran smoother afterward. I also had a similar issue with the car dying immediately after start. Do you have black soot and a foul smell coming out of the exhaust? A new MAF fixed the issue. GL on the repairs

I haven't been able to start my car long enough to observe anything coming out of the exhaust. I'm going to check my MAF with meter. I've already cleaned it but somewhere deep down my gut I think is a fuel issue. Lost of pressure or clogged injectors as its been stored for 12 years. Ecu capacitor replacement is def on my list but I'm trying to isolate the issue and it's so hard to do considering all the modifications. LOL

Repaired my running '94 LS400 caps as a precaution against cap failure and it has been running fine for months. My '93 ECU failed just recently so I replaced the caps with recommended Digikey caps and reinstalled the ECU and it ran fine at first with only slight hesitation coming off idle. I had then been to my junk yard haunts to find another '93/'94 ECU as a backup in case of failure on the road I would have a spare in the trunk. Lucky I did because I found one that had been repaired by someone and had a warranty sticker on it. Also lucky I had it in the trunk of my '93 when on one of my 300 mile road trips the original that I repaired failed after reaching my destination; turned it off and a short time later tried to turn it back on and it showed typical bad ECU symptoms. Got my tools and the warranted ECU out and installed it. The unit ran like a charm. Opened up the one I repaired (not) and could find no solder bridges, corrosion, etc. I had also been checking deals online for a backup for the '94 and was corresponding with a potential ECU shop about my cap repairs The response I got was:

Hello, we see these all the time, where people change the caps before hand.
Just changing the caps will not repair anything.
Very rare situation for cap change alone to make a difference so it
looks like you got lucky once.
If it isn't working right, then it obviously isn't right.
I'm sure we can restore it, but sorry I can not tell anything from the pic.
We can overhaul it at $250. w/5yr warranty, quick turnaround time.
Here is the listing for that:
Ebay item # 183784065942

The listing we are speaking through now,
is to buy our ECU, and yes we definitely want the core.
Thanks, Andre'

Any comments on this guy's response? Do you think there is an flash update or some other high failure component that we need to know about?

Hi Yamae,

Do you have a picture of a good trace for C102 on a 89661-50220 ECM?

Thanks in advance

Al

See the 5th photo of the post #240.
https://www.clublexus.com/forums/att...ps654e510e.jpg
The positive side of C102 is connected to the big diode D104 and the negative side to the ground, I believe.

You don't need to flash at all. Just replace those infamous capacitors. You can find many people who are happy on the forum here. They just changed those QAS capacitors and the car runs like a new. That guy you introduced is like a so called stealership. I don't mean all the dealerships are so.

Thanks Yamae. I trust you. I am still puzzled why the original '93 ECU worked (except for a slight hesitation coming off idle) for 3 weeks and then failed whereas the '94 I repaired has worked for 3 years. That '94 had no board damage at all but the '93 had some slight leakage of 10 uf cap C103. There was some residue on the board but I carefully removed that and tested for continuity as best that I could without benefit of a ECU schematic. With C103 removed I could find no shorts to ground on the + via and good continuity from the - via to other -via caps in that area. There was also good continuity of each via to both sides of the board so I don't think the plated through holes were damaged. However, there could be opens on the internal planes that wouldn't be visible from the top side that I couldn't check without benefit of a schematic of the ECU that would identify hidden traces. I re-populated the entire board with new Chemi-Con caps you recommended from Digikey. I also know that if these caps are used in switching regulators, the question of stability comes up since gain and phase margin could be affected by ESR of the caps. Are there other small surface mounted caps that are used in the feedback networks that might have been damaged in the areas where the electrolytic caps were. Some small 0201 caps near the larger electrolytic caps that might have been accidentally removed when I replaced the larger caps. Anyway, I am still haunting junk yards within a 200 mile radius in hopes of finding other ECUs before the others get to them. Is there a way to obtain a schematic of the ECUs without violating your position with Lexus. I worked as a consultant to a small company, Wavecom, designing Machine-to-Machine cell transmitter and receiver circuits for Denso about 10 years ago and remember having close relationships with Denso engineers. My wife and I love our Lexus's and don't want to let them go for newer models.

Unfortunately Toyota or Denso never releases any schematics at all. All we need to do is the reverse engineering. Sometimes a good X-ray machine is needed to investigate how the internal layers are consisting of.

I understand that you are one of few people who understand the BODE plot and how important it is to control the phase and the gain. I used to design both switching and series voltage regulators and I always plotted those to check the margin. Those ECUs were designed in 80s when very very low ESR electrolytic capacitors were not yet released from capacitor manufacturers but as far as I knew, those margins were well thought of. As long as I did experiments, using many of latest low ESR electrolytic capacitors, the regulators in the ECU do not cause any stability problems. But once a high capacitance SMD ceramic capacitor is used replacing an electrolytic capacitor, there happens stability problem and sometimes a strong oscillation is caused.

Without analyzing your '93 ECU myself, I can't say enough but judging from the symptom "slight hesitation coming off idle", there must be some problem lying. I wonder why it happens. The reason why so may be the key to investigate your '93 ECU. If I were living close to you, I could be analyzing the ECU together with you.