When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
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.
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).
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 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?
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?
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.
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.
Thanks again Yamae. My home equipment is not what I'm used to when I service my clients. Most have binocular microscopes that allow high resolution inspection and repair but I only have a 4X magnifying glass. My analog solder station also has just failed so I need to get a newer digital one that regulates the tip temperature when trying to solder/unsolder vias attached to ground or voltage planes. I know what you mean by the effect of the ESR and ESL of the cap on stability. I have done designs where I had to use a very low ESR cap and then put in series a known low value precision resistor to stabilize because of the wide tolerance of ESR in electrolytics. My background is primarily in RF design but I also usually do the power supply designs for my customer's boards. As you know the temperature extremes and the very wide swings of the 12VDC during cranking make automotive electronic designs difficult. Not really much difference in RF and power design just the operating frequencies, the equipment used, and, as you say, Bode analysis. I was showing my wife an area of the board last night when she wanted to see the difficulty of the repair and I see a cold solder splash across an unpopulated surface mounted cap. This may be the problem. I will report back.
It is May 29, 2019, i hope the links in the 1st post on this thread still work so I can order the caps for my 95 LS. I live in Arizona, my LS has 260k and my caps most definitely need to be replaced. I currently have no a/c, no power when accelerating(like i am pulling a boat or heavy load) and CEL with no codes when scanner is plugged in. I will need to find someone here in Phoenix to do the job as well.
Yep, everything is relatively current. I just updated my ECU (95 sc300) using all these instructions. I purchased my capacitors (2 sets) from Digikey. Caps plus shipping was about $14. Car would run for about 1 minute, then get extremely rough and die. I would wait 5 minutes, rinse & repeat. I didn't even do any significant troubleshooting, other than look into error code. After I did the update, I've not had a single issue. Have put about 2k miles on the car since.
Thanks again Yamae. My home equipment is not what I'm used to when I service my clients. Most have binocular microscopes that allow high resolution inspection and repair but I only have a 4X magnifying glass. My analog solder station also has just failed so I need to get a newer digital one that regulates the tip temperature when trying to solder/unsolder vias attached to ground or voltage planes. I know what you mean by the effect of the ESR and ESL of the cap on stability. I have done designs where I had to use a very low ESR cap and then put in series a known low value precision resistor to stabilize because of the wide tolerance of ESR in electrolytics. My background is primarily in RF design but I also usually do the power supply designs for my customer's boards. As you know the temperature extremes and the very wide swings of the 12VDC during cranking make automotive electronic designs difficult. Not really much difference in RF and power design just the operating frequencies, the equipment used, and, as you say, Bode analysis. I was showing my wife an area of the board last night when she wanted to see the difficulty of the repair and I see a cold solder splash across an unpopulated surface mounted cap. This may be the problem. I will report back.
Update. Well Yamae I replaced my old Weller analog solder station with a Hakko digital one which regulates the tip temperature and it works great. However, I'm afraid there is internal plane damage around C103. This 10 uf cap had been leaking. With C103 removed I can ring from the -via to other grounds in the area and get good continuity. I can't ring the +via to any other connection so it must attach to something using an internal trace. If C103 is part of a buck-boost forward converter or a flyback converter it is possibly attached to an inductor,transformer or a diode. A hard wire to that inductor would maybe work but I don't know what part of the power supply is associated with C103. Can you possibly identify what the +via attaches to?
I also have access to a repaired and warranted California speced '93 Lexus LS 400 ECU, 89661-50151. Will this unit work on my Fed speced '93 LS 400 (original ECU PN 89661-50140)?
Update. Well Yamae I replaced my old Weller analog solder station with a Hakko digital one which regulates the tip temperature and it works great. However, I'm afraid there is internal plane damage around C103. This 10 uf cap had been leaking. With C103 removed I can ring from the -via to other grounds in the area and get good continuity. I can't ring the +via to any other connection so it must attach to something using an internal trace. If C103 is part of a buck-boost forward converter or a flyback converter it is possibly attached to an inductor,transformer or a diode. A hard wire to that inductor would maybe work but I don't know what part of the power supply is associated with C103. Can you possibly identify what the +via attaches to?
I also have access to a repaired and warranted California speced '93 Lexus LS 400 ECU, 89661-50151. Will this unit work on my Fed speced '93 LS 400 (original ECU PN 89661-50140)?
My specialty is mainly about ECUs for JDM Gen2 and after. Sorry that I don't know much about Gen1 although I have fixed them a lot replacing capacitors and some other parts just doing the reverse engineering. But I haven't touched Gen1 ECUs for several years now and I don't have any references any more at my hand. In Japan, Gen1s were totally gone and Gen2s are just few now. So I have no idea how C103 is connected to the internal plane. But generally speaking electrolytic capacitors are used to remove ripples of DC lines and the negative side lead wire is always connected to ground plane or trace. The positive side to in/output lines of regulators. I hope this may help you to analyze the connection.
Regarding the ECU's compatibility, as long as the model year is the same, the California spec one usually works OK in Federal models although the engine power is a bit less.
My specialty is mainly about ECUs for JDM Gen2 and after. Sorry that I don't know much about Gen1 although I have fixed them a lot replacing capacitors and some other parts just doing the reverse engineering. But I haven't touched Gen1 ECUs for several years now and I don't have any references any more at my hand. In Japan, Gen1s were totally gone and Gen2s are just few now. So I have no idea how C103 is connected to the internal plane. But generally speaking electrolytic capacitors are used to remove ripples of DC lines and the negative side lead wire is always connected to ground plane or trace. The positive side to in/output lines of regulators. I hope this may help you to analyze the connection.
Regarding the ECU's compatibility, as long as the model year is the same, the California spec one usually works OK in Federal models although the engine power is a bit less.
Update to Yamae. I bought the California unit. Installed this AM and '93 LS400 immediately cranked. Short town and highway road test indicates smooth operation. I will run this one for intensive testing for the next month or so. I probably won't unseal this unit even though it may have board damage since it will be used as a backup ECU. The cost was very good. I have established a correspondence with the seller who has told me the cap PNs and they are the ones you recommended. He shared that like me, he also is having a hard time finding junk yard units that don't have board damage. He says that out of every 100 units only about 5 turn out to be repairable due to board damage. I plan to continue to reverse engineer the failed '93 ECU where the C103 part leaked onto the board. Maybe I can find a way to hard wire traces to appropriate components that will afford stability and acceptable ripple assuming other traces have not been destroyed in that area. At any rate I now have a backup for my '93 and '94 that will serve us for long trips since Jane and I both travel in one of them at a time. Now on to my instrument panel debug where the power supply for the fluorescent tube light is failing in my '93. I think there is a repair tutorial for that on this forum. Again, thanks for your help.
05-23-19, 04:05 PM
perhaps an ECU problem?
