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All my crazy Lexus issues SOLVED!! (ECU-leaking capacitor)

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LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

All my crazy Lexus issues SOLVED!! (ECU-leaking capacitor)

Old 10-08-18, 07:09 AM
  #1501  
janelur
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Default 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) .
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Old 10-14-18, 10:25 AM
  #1502  
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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?
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Old 10-14-18, 08:44 PM
  #1503  
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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!
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Old 10-17-18, 11:19 AM
  #1504  
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Yamae has a ripple test for the ECU here:
https://www.clublexus.com/forums/ls-...-by-yamae.html
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Old 10-30-18, 01:07 PM
  #1505  
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Any idea how much it would cost to have this shipped out to get the capacitors replaced?
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Old 10-30-18, 05:16 PM
  #1506  
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Originally Posted by DerekD1010 View Post
Any idea how much it would cost to have this shipped out to get the capacitors replaced?
Send it to driftmotion in Montclair Ca,and 90 bucks later its rebuilt and your problem is solved.
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Old 11-11-18, 06:55 PM
  #1507  
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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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Old 11-12-18, 05:39 PM
  #1508  
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Originally Posted by TRDMan View Post
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.)
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.
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Old 11-13-18, 01:21 AM
  #1509  
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Originally Posted by Yamae View Post
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.
My car is a VVT-i 5 speed AT. I did not experience any transmission issues while my ECU was having problems. This could be attributed to the fact that I only experienced my ECU issues over the course of three days; I parked my SC400 on the third day and drove my other car while I waited for the capacitors to be replaced. Perhaps I did not drive my SC400 enough to experience any of the transmission issues that usually arise.
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Old 11-15-18, 09:09 PM
  #1510  
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I am considering buying a 1998 LS400 from a private seller. The car has some problems that his mechanic canít 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:

ďThe only issues Iíve 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 canít 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 Ė 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 (Iím 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 Ė 200 miles after resetting.

The only issues Iíve noticed as Iíve 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. Iíve monitored my fuel consumption since obtaining the car and have consistently achieved 23 - 27 mpg, with higher fuel economy during longer, highway trips. I havenít specifically noticed decreased mileage.

Live data Iíve 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 Ė 5%, LTFT increase to 28 %
∑ When applying load while driving: STFT -5 Ė 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 Ė 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 Ė 48 psi, he indicated that was good.

The only code Iíve ever had come up is the P0171, lean condition bank 1.

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Old 11-16-18, 08:53 PM
  #1511  
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Originally Posted by gmcbean View Post
I am considering buying a 1998 LS400 from a private seller. The car has some problems that his mechanic canít solve. I suspect the ECU but I would like to hear from some people who have much more experience than me.
------------------------
The only code Iíve ever had come up is the P0171, lean condition bank 1.
If it were the ECU capacitors problem, those symptoms wouldn't be common among a 98 and after. A simple ECU capacitor check can be done measuring the ripple voltage. The method can be found in the FAQ page.

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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Old 11-17-18, 09:17 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
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Old 11-17-18, 12:26 PM
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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 wouldnít show a leak or be in such a place where it would be hard to spot the leak?
We appreciate your help!
Greg
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Old Today, 03:58 AM
  #1514  
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Originally Posted by jamesdean9 View Post
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
I'd simply replace ECU capacitors in accordance with the post #1. Your " no acceleration when cold and jerks badly" issues are the typical symptoms of failing capacitors.
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