All my crazy Lexus issues SOLVED!! (ECU-leaking capacitor)
10-08-18, 06:09 AM
#1501
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Cold start problems
Thanks for this important and instructing information. I will solder new capacitors soon and hope it solves my cold start issue where the engine does not rev up as normal even if the Idle valve is wide open. .My LS 1990 has a loud hissing noise on cold start and it seems to come from the idle control valve area. I have heard that there is a valve in the cruise c unit that can leak and make a loud hissing. Another possibility is that the EGR valve is clogged so much that even if the idle control valve is fully opened the engine does not get enough cold start air??. I do belive that the engine is getting plenty of air to do the cold start but the old and bad capacitors are not able to give the needed puls time to injectors so that the fuel mix to the high amount of air makes it stall and not rev up. Anyone that may have thoughts on this issue. (Cold winters in Norway so this is a serious problem) .
10-14-18, 09:25 AM
#1502
HOLY MOLY THIS IS THE MOTHER OF ALL THREADS!!! There is just so damn much info here. Does anyone want to start a project to make it more cohesive or build an sub-thread for ECU repairs??? This is a lot to go through. AND I STILL DIDN'T FIND WHAT I NEEDED!!! 
The exploded view and instructions here for removing the ECU apply to the 95-97. The 90-94 is also behind the glove box, but mounted under it and on the front of the dash. I found instructions for an RHD model HERE. It's mirrored, but has good pics and detail.
I'm about 99% sure both my 1991 and 1994 need this work done. I'll pull the ECUs and decide between DIY and shipping them off. Hopefully they boards aren't f'ed up.
EDIT: Is there anyone in Oregon who fixes these?
The exploded view and instructions here for removing the ECU apply to the 95-97. The 90-94 is also behind the glove box, but mounted under it and on the front of the dash. I found instructions for an RHD model HERE. It's mirrored, but has good pics and detail.
I'm about 99% sure both my 1991 and 1994 need this work done. I'll pull the ECUs and decide between DIY and shipping them off. Hopefully they boards aren't f'ed up.
EDIT: Is there anyone in Oregon who fixes these?
10-14-18, 07:44 PM
#1503
So I pick up this 1991 with a dead electrical system. It starts right up, shifts pretty well, the entire front suspension is beat, the steering is mushy, the left front wheel bearing is going out and the PS pump is dead. SO I DRIVE IT 131 MILES HOME!
About halfway, and hour or so, it dies on the highway. Luckily I'm close to a city and it cuts off right as I'm approaching an exit. I just make it to the top before I run out of momentum entirely. Dead battery = dead alternator. Take it to Auto Zone and get it charged. Back on the road, off the highway, and 15 minutes later it stalls out again. But just as it does EVERYTHING COMES ON! I pop the hood and the negative terminal has come off. I hook it back up and head on. I'm super happy because I can finally adjust the seat. Everything works, but the dash keeps blinking, the TRAC light is blinking, and when I make it home the battery is drained again.
So I'm thinking ECU. I pull it out, and aside from a patina of fine white corrosion on the outside, this thing looks BRAND NEW. So I snap some pics and button it up.
it's a 89661-50042. Based on my problems, I'm guessing I should go ahead and send this to be rebuilt. I've scanned through this thread and there doesn't seem to be any easy manner of testing, and since this was pretty dusty, it's unlikely to have already been repaired.
Any objections? Questions? Want to see pics?
For my next trick I'll be removing the ECU on a 1994!
About halfway, and hour or so, it dies on the highway. Luckily I'm close to a city and it cuts off right as I'm approaching an exit. I just make it to the top before I run out of momentum entirely. Dead battery = dead alternator. Take it to Auto Zone and get it charged. Back on the road, off the highway, and 15 minutes later it stalls out again. But just as it does EVERYTHING COMES ON! I pop the hood and the negative terminal has come off. I hook it back up and head on. I'm super happy because I can finally adjust the seat. Everything works, but the dash keeps blinking, the TRAC light is blinking, and when I make it home the battery is drained again.
So I'm thinking ECU. I pull it out, and aside from a patina of fine white corrosion on the outside, this thing looks BRAND NEW. So I snap some pics and button it up.
it's a 89661-50042. Based on my problems, I'm guessing I should go ahead and send this to be rebuilt. I've scanned through this thread and there doesn't seem to be any easy manner of testing, and since this was pretty dusty, it's unlikely to have already been repaired.
Any objections? Questions? Want to see pics?
For my next trick I'll be removing the ECU on a 1994!
10-30-18, 04:16 PM
#1506
Racer
11-11-18, 05:55 PM
#1507
I just wanted to share my 1998 SC400's bad ECU capacitor symptoms in case anyone is unsure. All these issues went away after changing the capacitors, which had no evidence of leaks but were the ones that Yamae listed as problematic. The capacitors were changed five months ago and none of these issues return since then.
- My car would crank but will not start. If I waited 15 minutes and tried again, it would start like normal.
- The idle RPM was very low while the car was in drive. I stalled twice at stop signs until I turn on the A/C to keep the idle higher.
- My car's battery, which was two years old at the time, would completely drain overnight (about 8 hours of sitting.)
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Yamae (11-13-18)
11-12-18, 04:39 PM
#1508
Moderator
I just wanted to share my 1998 SC400's bad ECU capacitor symptoms in case anyone is unsure. All these issues went away after changing the capacitors, which had no evidence of leaks but were the ones that Yamae listed as problematic. The capacitors were changed five months ago and none of these issues return since then.
- My car would crank but will not start. If I waited 15 minutes and tried again, it would start like normal.
- The idle RPM was very low while the car was in drive. I stalled twice at stop signs until I turn on the A/C to keep the idle higher.
- My car's battery, which was two years old at the time, would completely drain overnight (about 8 hours of sitting.)
Yes, QAS electrolytic capacitors are problematic because those fail quicker than other conventional capacitors. The internal impedance or the ESR is badly increased at the end of the life, so it would be better to replace those before that. One of simple ideas to judge is to check the ripple level posted in the FAQ page.
I have a question TRDMan. Is your 98 SC400 equipped with a manual transmission or a 5 speeds AT?
In my experience, those 98 and after models (VVT-i engine with 5 speeds AT) tend to have AT gear shift problems when those capacitors begin to fail. I don't see this in your descriptions and I just want to confirm. Thanks, in advance.
11-13-18, 12:21 AM
#1509
Thanks for sharing your experience with detailed descriptions, TRDMan. Your post would help others, I'm sure. It would be nice of you, if you were able to post it at the SC400 Forum too.
Yes, QAS electrolytic capacitors are problematic because those fail quicker than other conventional capacitors. The internal impedance or the ESR is badly increased at the end of the life, so it would be better to replace those before that. One of simple ideas to judge is to check the ripple level posted in the FAQ page.
I have a question TRDMan. Is your 98 SC400 equipped with a manual transmission or a 5 speeds AT?
In my experience, those 98 and after models (VVT-i engine with 5 speeds AT) tend to have AT gear shift problems when those capacitors begin to fail. I don't see this in your descriptions and I just want to confirm. Thanks, in advance.
Yes, QAS electrolytic capacitors are problematic because those fail quicker than other conventional capacitors. The internal impedance or the ESR is badly increased at the end of the life, so it would be better to replace those before that. One of simple ideas to judge is to check the ripple level posted in the FAQ page.
I have a question TRDMan. Is your 98 SC400 equipped with a manual transmission or a 5 speeds AT?
In my experience, those 98 and after models (VVT-i engine with 5 speeds AT) tend to have AT gear shift problems when those capacitors begin to fail. I don't see this in your descriptions and I just want to confirm. Thanks, in advance.
11-15-18, 08:09 PM
#1510
10th Gear
I am considering buying a 1998 LS400 from a private seller. The car has some problems that his mechanic can’t solve. I suspect the ECU but I would like to hear from some people who have much more experience than me. I did ask the seller to send me a summary of the problems and the work that has been done. Here is what he sent:
“The only issues I’ve encountered since obtaining the vehicle include intermittent CEL and starter failure. The starter, as you know, was replaced in approximately 08/2017 with about 105k. During the repair the shop also replaced the throttle body gasket (and I want to say the manifold plenum or something was also replaced, this may be the incorrect item, I can’t remember from memory. It is listed on the service document).
The CEL first occurred around May 2016 and has been on and off since then for approximately half of the time. The longest time without the light was from 09/17 – 09/18.
After May 2016: Replaced air filter, and cleaned MAF sensor. Replaced gas cap. Then replaced the MAF sensor with aftermarket sensor, and cleaned the throttle body (without disassembling). This whole process probably went about 6 months, then the light was off for approximately a year and would sometimes come back on for a few moments while driving, or when first starting the vehicle. I generally attributed this to changes in humidity/temperature, as it seemed to be on more during the colder, winter months. Never experienced any issues with driveability, nor with rough idle on cold start.
Since Sept 2018, approx. 128k miles:
· Replaced air filter, cleaned MAF sensor. Disassembled throttle body and thoroughly cleaned, replaced gasket. Disconnected ECU/reset CEL. Light returned.
· Identified air intake tube crack and replaced with OEM tube. Reset ECU, light returned.
· Checked all vacuum hoses and sprayed carb cleaner with engine running to identify leaks, none found.
· Replaced PCV valve with OEM part.
· Mechanic ran smoke test, identified leak where MAF sensor connects to MAF sensor housing (after air box), replaced o-ring, mitigated air leak.
· Mechanic removed and cleaned a plugged/clogged OCV (I’m assuming this was the driver side as I believe passenger is difficult to access). ECU reset, light returned.
The light would come back on anywhere between 20 – 200 miles after resetting.
The only issues I’ve noticed as I’ve become hyper focused on performance are: rough idle on warm start (after driving for 20 miles, letting sit for an hour, then restarting, for example), with addition of what I might call sluggish first acceleration on cold start. I’ve monitored my fuel consumption since obtaining the car and have consistently achieved 23 - 27 mpg, with higher fuel economy during longer, highway trips. I haven’t specifically noticed decreased mileage.
Live data I’ve tracked (not stored digitally, just in my head):
Fuel Trim:
· On idle: STFT and LTFT approximately 15% and 21%, respectively (both banks similar).
· After applying static load (neutral or in park): STFT decrease to 0 – 5%, LTFT increase to 28 %
· When applying load while driving: STFT -5 – 5%, LTFT 34% (once load is reduced, LTFT immediately decreased back to 21%, STFT gradually increase back to 12-15%).
Bank 1 Front O2 sensor:
· Fluctuates between ~0.25 – 0.75 V while driving. This is the only sensor I was particularly concerned about and these the only one I have specifically tracked.
Fuel Pressure:
· Mechanic states the fuel pressure (I think the term he used was rail pressure?) was 47 – 48 psi, he indicated that was good.
The only code I’ve ever had come up is the P0171, lean condition bank 1.
“The only issues I’ve encountered since obtaining the vehicle include intermittent CEL and starter failure. The starter, as you know, was replaced in approximately 08/2017 with about 105k. During the repair the shop also replaced the throttle body gasket (and I want to say the manifold plenum or something was also replaced, this may be the incorrect item, I can’t remember from memory. It is listed on the service document).
The CEL first occurred around May 2016 and has been on and off since then for approximately half of the time. The longest time without the light was from 09/17 – 09/18.
After May 2016: Replaced air filter, and cleaned MAF sensor. Replaced gas cap. Then replaced the MAF sensor with aftermarket sensor, and cleaned the throttle body (without disassembling). This whole process probably went about 6 months, then the light was off for approximately a year and would sometimes come back on for a few moments while driving, or when first starting the vehicle. I generally attributed this to changes in humidity/temperature, as it seemed to be on more during the colder, winter months. Never experienced any issues with driveability, nor with rough idle on cold start.
Since Sept 2018, approx. 128k miles:
· Replaced air filter, cleaned MAF sensor. Disassembled throttle body and thoroughly cleaned, replaced gasket. Disconnected ECU/reset CEL. Light returned.
· Identified air intake tube crack and replaced with OEM tube. Reset ECU, light returned.
· Checked all vacuum hoses and sprayed carb cleaner with engine running to identify leaks, none found.
· Replaced PCV valve with OEM part.
· Mechanic ran smoke test, identified leak where MAF sensor connects to MAF sensor housing (after air box), replaced o-ring, mitigated air leak.
· Mechanic removed and cleaned a plugged/clogged OCV (I’m assuming this was the driver side as I believe passenger is difficult to access). ECU reset, light returned.
The light would come back on anywhere between 20 – 200 miles after resetting.
The only issues I’ve noticed as I’ve become hyper focused on performance are: rough idle on warm start (after driving for 20 miles, letting sit for an hour, then restarting, for example), with addition of what I might call sluggish first acceleration on cold start. I’ve monitored my fuel consumption since obtaining the car and have consistently achieved 23 - 27 mpg, with higher fuel economy during longer, highway trips. I haven’t specifically noticed decreased mileage.
Live data I’ve tracked (not stored digitally, just in my head):
Fuel Trim:
· On idle: STFT and LTFT approximately 15% and 21%, respectively (both banks similar).
· After applying static load (neutral or in park): STFT decrease to 0 – 5%, LTFT increase to 28 %
· When applying load while driving: STFT -5 – 5%, LTFT 34% (once load is reduced, LTFT immediately decreased back to 21%, STFT gradually increase back to 12-15%).
Bank 1 Front O2 sensor:
· Fluctuates between ~0.25 – 0.75 V while driving. This is the only sensor I was particularly concerned about and these the only one I have specifically tracked.
Fuel Pressure:
· Mechanic states the fuel pressure (I think the term he used was rail pressure?) was 47 – 48 psi, he indicated that was good.
The only code I’ve ever had come up is the P0171, lean condition bank 1.
11-16-18, 07:53 PM
#1511
Moderator
I am considering buying a 1998 LS400 from a private seller. The car has some problems that his mechanic can’t solve. I suspect the ECU but I would like to hear from some people who have much more experience than me.
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The only code I’ve ever had come up is the P0171, lean condition bank 1.
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The only code I’ve ever had come up is the P0171, lean condition bank 1.
Generally speaking a non genuine MAF is not quite OK for a 1UZ-FE engine especially with the VVT-i. You'd better compare the readout voltage with a good genuine one or simply swap it to troubleshoot quicker.
The code P0171 only is mostly caused by the simple vacuum leak. To use a vacuum gauge will help you to judge. You need to check intake lines thoroughly. Sometimes the deteriorated gasket used at the intake manifold causes it. There are many other vacuum lines such as the canister line, PCV lines, the brake booster line, the power steering control line and others. Sometimes the intake de-resonator is cracked or it's ventilation lines are broken. A smoke machine is useful to find the exact leaking point.
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gmcbean (11-17-18)
11-17-18, 08:17 AM
#1512
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hi guys I know this maybe the wrong thread but I need help I have a 96 Lexus ls 400 it is missing and using fuel like crazy I have replaced the plugs and wires the coolant temp sensor the fuel pump and I have no clue where to go from here the check engine flashes seems worse when its cold after it warms up the problem seems to stop or least decrease a bit it has no acceleration when cold and jerks badly so if you guys have any ideas please let me know
11-17-18, 11:26 AM
#1513
10th Gear
Thanks Yamae for your helpful reply.
The owner had his mechanic do a smoke test. One leak was found and repaired but the CEL still comes back on. I know this sounds like a crazy question but is there any possible way that a smoke test wouldn’t show a leak or be in such a place where it would be hard to spot the leak?
We appreciate your help!
Greg
The owner had his mechanic do a smoke test. One leak was found and repaired but the CEL still comes back on. I know this sounds like a crazy question but is there any possible way that a smoke test wouldn’t show a leak or be in such a place where it would be hard to spot the leak?
We appreciate your help!
Greg
11-21-18, 02:58 AM
#1514
Moderator
hi guys I know this maybe the wrong thread but I need help I have a 96 Lexus ls 400 it is missing and using fuel like crazy I have replaced the plugs and wires the coolant temp sensor the fuel pump and I have no clue where to go from here the check engine flashes seems worse when its cold after it warms up the problem seems to stop or least decrease a bit it has no acceleration when cold and jerks badly so if you guys have any ideas please let me know
11-28-18, 09:26 AM
#1515
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First off thank you for all the information in this thread. I just bought a 1990 LS400 at the beginning on November with 157,000 miles. The seller told me about a few of the issues the car had and when I test drove it none of those seemed to be apparent. I have been reading through most of this site when researching cars and have been on the look out for a car that would be more reliable than my 2000 Dodge truck, spent more time in shop than on the road, and decided on a Lexus. Now call me crazy for getting a 30 year old car but from the wealth of knowledge here I think I made the right decision.
After reading this thread and what the car was doing I decided to sent the ECU out to get recapped. Known issues are as follows:
High idle upon start up at around 2,000 rpms
Not wanting to start/would take around 30 seconds of cranking before the car would fire up.
Hesitation/vibration/jerking sensation at around 42-48 miles per hour but only if I would try to hold that speed, if I would speed up through that range or let the car coast back down I would not experience that sensation at all.
The first two issues seem to have been resolved with the recap. The third issues I have not got to test to see if it is resolved still tied up with out of state inspection and getting title, tags, insurance...work schedule for me has been a little busy. There is an earlier post in this thread I can not find at the moment but he used a guy that repaired old Sega arcade games, I had him redo mine as well. He said my ECU was one of the better ones he had seen. (No pics sorry) From reading and finding the original QA stamp date on mine I appeared to be all original. May 05 1990 was the stamp on the side. Ken who did mine said it had no leaking caps but a few were slightly bulged.
After reading this thread and what the car was doing I decided to sent the ECU out to get recapped. Known issues are as follows:
High idle upon start up at around 2,000 rpms
Not wanting to start/would take around 30 seconds of cranking before the car would fire up.
Hesitation/vibration/jerking sensation at around 42-48 miles per hour but only if I would try to hold that speed, if I would speed up through that range or let the car coast back down I would not experience that sensation at all.
The first two issues seem to have been resolved with the recap. The third issues I have not got to test to see if it is resolved still tied up with out of state inspection and getting title, tags, insurance...work schedule for me has been a little busy. There is an earlier post in this thread I can not find at the moment but he used a guy that repaired old Sega arcade games, I had him redo mine as well. He said my ECU was one of the better ones he had seen. (No pics sorry) From reading and finding the original QA stamp date on mine I appeared to be all original. May 05 1990 was the stamp on the side. Ken who did mine said it had no leaking caps but a few were slightly bulged.