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Thanks Yamae for the quick answer. Should you still clean and flux both sides? Is it ok to use old leaded good quality solder? or buy new lead free? Thank you for the help? Will open up ecm soon. Pretty certain this is the problem. Intermittent misfire #6,less on #4 cyl. check engine light etc.Has new plugs, wires ohm ok. no secondary leakage found? car runs fine then out of the blue it happens .
Thanks Yamae for the quick answer. Should you still clean and flux both sides? Is it ok to use old leaded good quality solder? or buy new lead free? Thank you for the help? Will open up ecm soon. Pretty certain this is the problem. Intermittent misfire #6,less on #4 cyl. check engine light etc.Has new plugs, wires ohm ok. no secondary leakage found? car runs fine then out of the blue it happens .
You are welcome. As long as "no clean" flux is used, you don't need to clean but what is written here would be your help.
The solder used for LS400 contains lead because Toyota had never used the lead free solder for LS400. The regulation RoHS was not yet considered at that time. You'd better to use good old classic leaded solder.
Hope your ECU board is not yet corroded by the leaked QAS liquid and your capacitors replacement will be going well. It would be nice of you if you can come back and report the results.
I was having codes P300, P302, P303, P304,P305, P306, P308 and P172 all pop up. Before I found this thread I threw new plugs, wires, and coils. Codes still popped up and car would lose rpm at stop lights and eventually stall. I ordered capacitors and took the ECU to a local electronics shop for him to solder. He fixed the capacitors and a few resistors along with the copper tracks that melted away from the acid. He had the capacitors on hand. He charged me $140 but its because he made other repairs on the board and not just solder the capacitors.
Installed it today and no check engine light on. Car has tons of power now. Thank god I found this thread. Shop is in Norwalk Ca if anyones interested.
Hey all. I set out on doing this capacitor replacement got caps, then some time later found time to remove the ecu.
My problems are seemingly a miss fire and lack of power. the problem only shows itself after the car is up to temperature. and is especially apparent when going 75 and trying to accelerate on a hill.
I have the weird red light on with the six bars on it, 3 on each side. of which i dont know what it means. I did have an idle problem, it was always high and it wouldnt go over 80 very well. but then after replacing what could have been the original fuel filter the idle is fine now and will go over 80 but still has the missfire. I dont know if a car can run on a 26 yr old fuel filter but there was 'stuff' in it. I mean, the new one was like an empty soda can the old one had weight to it. all kinds of stuff came out of it.
I went to replace the caps today and when i get the ecu out and opened, its obvious that the caps have been replaced already. they look in good shape, you can see where the board around the 220mf 50v cap area has been cleaned. There was also a date written on the ecu of 2010 , and the cap brands are the ones in the description opposed to the ones i could get at this time.
So, could the replacements have failed? in 9 years?
And what other things can i do to find my problem. i took one plug out to examine it. seems fine, caps and rotors seem fine. And if you being an experienced lexus owner/repair person could explain any procedures in detail would be helpful.
Over time the check engine light and the trac light would go on, I could floor it from a stop up to maybe 45-50 then they would both go out. Well they arent going out anymore.
I'd like to keep the car, but its getting difficult to find exterior parts (currently i need a driver side fog lamp assy) and i dont want to throw parts at it for nothing. And when i bring it to a mechanic the 1st thing they want to do is grab their odb2 and have the computer tell them whats wrong... they find out its odb1, they dont know how to fix it.
Any help would be appreciated. I took a couple pics of the ecu. which does not really show anything conclusive. and i was entertaining making a video of the problem its having while driving. again just a miss fire. and lack of power. let me know if that would help.
The dash light with the 3 bars on each side may be a parking lamp failure.
On cars this old various connectors are now brittle with the years of heat cycling Many sensors as well may be due. Would have to check those to verify a good contact.
I did have an idle problem, it was always high and it wouldnt go over 80 very well. but then after replacing what could have been the original fuel filter the idle is fine now and will go over 80 but still has the missfire.
This explanation reminds me of a weak fuel pump. A badly clogged fuel filter becomes a too much load for the pump and there goes too much current to coils in the pump motor via brushes and the commutator causing extra heat. This often shorten the life of the pump motor and the torque becomes less. The pump can't supply enough fuel and you'd have power problem at higher speed.
Originally Posted by lobsterman
There was also a date written on the ecu of 2010 , and the cap brands are the ones in the description opposed to the ones i could get at this time.
So, could the replacements have failed? in 9 years?
Judging from the year 2010, the capacitors used were not correct ones. Probably those are only selected seeing the capacitance and the voltage. You'd better to use capacitors listed in the capacitor's thread.
My 1998 Lexus LX40 will not start. The dreaded red light shows on the dash and I've replaced the battery in my key, attempted to get the car to recognize the key but it still won't start. Over the past several months this has been going on and now just won't start. I noticed that the car loses power while driving as well.
I've decided to remove the ECU and check for corrosion of the capacitors and I've posted a photo below. I'm not seeing anything that jumps out and I thought I would let you educated minds have a look.
@Mauser has graciously offered some advice. I'm wondering if I could purchase another used ECU like this off ebay and swap it in to fix my issues? Would I need to reprogram my keys?
Hard to tell due to the angle but make sure none of the caps with an "X" on top are bulging on the top. They should all be perfectly flat. Also, I don't think the 98+ ECU's had nearly as high a failure rate as the earlier models.
My 1998 Lexus LX40 will not start. The dreaded red light shows on the dash and I've replaced the battery in my key, attempted to get the car to recognize the key but it still won't start. Over the past several months this has been going on and now just won't start. I noticed that the car loses power while driving as well.
I've decided to remove the ECU and check for corrosion of the capacitors and I've posted a photo below. I'm not seeing anything that jumps out and I thought I would let you educated minds have a look.
@Mauser has graciously offered some advice. I'm wondering if I could purchase another used ECU like this off ebay and swap it in to fix my issues? Would I need to reprogram my keys?
I would do the ripple test first before I doubt the ECU. You can find the way to check the ripple at the FAQ.
Incidentally have you scanned?
I also have to inform you that when you swap the ECU, you need to rewrite or transplant the immobilizer data chip. This is not for everyone since it needs some skills and tools. So only buying another ECU is not OK.
The fuel pump was one of my thoughts as well. I was happy to find that the fuel filter was not inside the tank like some cars. Though there might be slight wisdom in putting it there. You'd replace the pump if you were there if it was bear to get to it and was cheap enough. I dunno.
But, recently the car seems to have changed. I get more power than before, and had it up to 110mph. Y'all know what it takes to get there. Anyone that drives this car, see your thinking of it now... There's still the little skip .. The car seemed to have eaten through 'most' of whatever the problem is. I suspect injector. But again, thats not something i ever troubleshooted before as a mechanical type, above average, person.Guess I'll get out my 1.5' 3/8 extension and my ear and see if that works..
Mayhaps it's that simple.
I'll leave updates for those that are curious or still have this vehicle or maybe have the same problems..Time passes............
Just a quick description to get it off my chest. Especially after finally reading 80% of this thread after I've been here 10 yrs.
Well, time for me to finally jump on this bandwagon. About 6 months ago with my 94 LS400, all of a sudden when pulling off from a stop sign or light (after it reached operating temp) it would go good up to 2k RPM and then felt like the fuel just shut off. Let off the gas pedal a touch and it would kick back in but go slowly, so I was thinking either fuel filter or pump but if I downshifted to 2nd it would take off good up to 3k RPM and then die the same way. Then I thought, maybe the ECU is bad. So I changed the ECU with the one I pulled from my 93 when I junked that. That one had it's own problems like the A/C didn't work, shifted weird, high idle, and other stuff but I still used it cuz I'm only fixing things on this car to get me around 5 miles a day. (waiting for it to literally fall apart) But a couple days ago I go out and came back, the car was fine. A few hours later I go to start it and it seemed like it would start for 1-2 seconds and die. Just what I need with all the other problems I have in my life. So I switched the ECUs again, put the 94 ECU back in, at least I can drive it slowly with it's problems. As I took out the bad one I could hear something rattling around inside. I opened it up to see if, just maybe, I can repair it. But there's no way my eyes are gonna let me fix this. These pics on here sure make it look alot bigger. The rattling was one of the caps burnt itself off. It was c104. So now I'm just driving it under 2k RPM til I can send out the one from the 93 when I can afford it. (fixed income sucks) Hopefully the board is still good and it can be fixed. I usually don't let other people work on my car, but this is different.
Just checking, is https://www.taninautoelectronix.com/ still the place to go and approximately what does it cost to recap a 93 LS ECU nowadays? (with the correct caps)
Thanks for listening to all that.
I would also like to thank Yamae for his knowledge.
Last edited by deanshark; 09-27-19 at 01:27 PM.
Reason: putting the right cap # c104
Happy that the monster thread was helpful. We've had two prior cars have ECU issues in this household. Knowing now, would have been nice to have been able to open them up and keep them going. Well, except for the Saturn SL2. Dad wasn't happy to have to buy another car but he grew to dislike the GM product after that experience. The 82 Maxima and father-in-law's '82 280ZX was another that were due to an ECU issue. I relayed to FIL I'd check his ECU but his mechanic had talked him into a major parts hunt-swap so by the time he'd dumped all the $ he was sick of it and sold it for a hurtful amount to get a Honda.
I've gone on to use the soldering iron for other fixes like replacing these micro switches in the mice:
Last edited by RA40; 09-26-19 at 10:21 PM.
Reason: additional
I think your '93 ECU is bad. Just changing caps as I did in my '93 with leaking caps didn't fix it and your cap falling off is not a good sign. The internal planes are likely toast from the leakage and the board is probably bad. I haunted local junk yards for several months and finally found a 93' that had been repaired and it worked. I did repair my '94 with new caps before the old ones leaked and the repair was successful. I finally bought a California spec unit that had been repaired for a good price and it works. I keep this unit with me on long trips as a back up. I still haunt the junk yards whenever a wrecked '93 or '94 shows up that was running when a collision stopped it under the assumption that the ECU had been repaired. If I find one that hasn't stopped due to a wreck I pull the ECU covers in the yard and check the caps for signs of leakage. If I see one that looks good I will take it home and replace the caps and use it as a permanent backup for the other LS400. I tried to trace the wiring on the '93 in hopes that I could surface wire it to make it work but so far that '93 won't work. Absent an XRAY machine that I used to have access to when I am working as an engineer I have given up on this one.
07-04-19, 05:54 AM
So I switched the ECUs again, put the 94 ECU back in, at least I can drive it slowly with it's problems. As I took out the bad one I could hear something rattling around inside. I opened it up to see if, just maybe, I can repair it. But there's no way my eyes are gonna let me fix this. These pics on here sure make it look alot bigger. 
The rattling was one of the caps burnt itself off. It was c104. So now I'm just driving it under 2k RPM til I can send out the one from the 93 when I can afford it. (fixed income sucks) Hopefully the board is still good and it can be fixed. I usually don't let other people work on my car, but this is different.
