So I found some old records from the first time the Lexus was taken to the shop. The mechanic wrote the code on the paperwork which was at the time P1346 VVT. I believe that is variable valve timing?

And their notes specified that the engine had very low compression which caused them to check the timing belt. As I mentioned in my first post, the engine eventually reset or possibly the ecu reset at which point it started cranking again. When that happened, the shop scoped the cam sensors and they looked fine.

The only other thing that happens sometimes on the car that may or may not be related is that upon starting the car, there will be a single click noise and then nothing at all. It seems like all power is temporarily gone. But when that happens, releasing the key from start position and trying again usually cranks the car as usual. Again, I'm not sure if this has anything to do with ecu, but if it does, then hopefully it will help.

Thanks again for all the help and also the expedience of it. I just got the notification via email that I had responses to my question. I'll check back more often or see if my settings can be adjusted to alert me more quickly.

 

Keep in mind that it doesn't matter whether the ECU came from your local pull-a-part, or is the original from your car, or even bought from a reputable place online, they all need new capacitors, and pretty much every technician besides yamae and myself aren't electrical engineers and they end up not using the correct type of premium brand Japanese low-ESR capacitors, which are more expensive, so even if a place online says they have been done, they almost certainly need to be redone - Be SURE to use the exact brands and part number capacitors I linked to in post #1 when you replace your capacitors!

 

Thank you sooo much to both you & Yamae for your help. Will have the new capacitors for my 91 LS tomorrow and hope it will run better. I'll let you know!

 

I thought I would ask finally if I have a capacitor issue with my 1994 LS. I've put so much effort into it this far but I'm still having nagging issues.

I'll get a rich start up condition every once in awhile where it will blow black smoke for about 20 seconds or so then totally stop. I'm pretty sure my oxygen sensors could be original, could that also be the issue?

It will shift harder than normal every once in awhile (I have the transmission cable adjusted properly and the fluid has all been exchanged.)

The temperature gauge will always read slightly above the middle but if you park it after driving and turn the key right back on, the needle will sit right in the middle where it's supposed to. I'm not sure if it is a cluster issue as I've had a flaky gas gauge repaired by BBA Reman and it's been fine otherwise. I don't recall if the gauge would sit in the middle before I had it repaired because I just got the car and sent the cluster away to be fixed after owning it for a couple of days.

Sometimes when starting, while it's cranking you can hear the engine slow down slightly. Other times it cranks fast like it's supposed to. The battery is good and the starter has never given me any other issues. Not sure if this is even related to the ECU but it seems strange enough to be.

Thanks!

 

the rich start up condition and possibly the hard shifting could be ECU capacitor related, the gauge reading and slow cranking, probably not

all LS400's will eventually get the ECU capacitor issue, and while it is the culprit in a great many nagging and intermittent issues on LS400, it certainly is not the be-all end-all cure for every LS400 issue!

My LS400 had the ECU capacitors fail, but have also had a couple of other unrelated problems such as a faulty Idle Air Control Valve bearing and alternator ruined by leaking power steering fluid.

before doing the ECU capacitors, I recommend you replace both temp sensors, the one for the EFI (2 wire) Toyota p/n 89422-20010 as well as the single wire sensor right beside it, which supplies the gauge temp info.

 

Thanks for the reply, I appreciate it. I will pull my ECU out very soon when I get the motivation.

Since I am scared to screw up my ECU, there is a guy local to me that offers the repair service and has excellent feedback on ebay. Is there anybody that you would recommend?

Also, I forgot to add that I have already replaced the ECU temp sensor but I will get the sensor for the gauge next.

 

Above is the way how to check ripples simply at the diagnostic connector. All you need are just a good multimeter and a capacitor. What I meant to say by "a good multimeter" is that the meter can measure up to 300KHz or higher. If not, the read out result is smaller.

Measure the AC voltage between "OP1" and "E1" in series with a film capacitor 0.47uF or so to eliminate the DC.

Celsior's "OP1" is internally connected to the engine temp sensor and "E1" to the signal ground of the ECU. I think LS400s 94-00 are the same. The read out voltage are preferred roughly speaking 40mV RMS or less.

_____________________
Below are for those who are interested in the detail.
The engine temp sensor is supplied the 5V regulated DC from the ECU via a resistor and you can measure the ripple voltage "Er" at this point some. In other words, the engine temp sensor is pulled up by a resistor to the DC 5V in the ECU. So you can check the ripple without opening the ECU box.

The relationship between "Er" and "real ripple voltage" are calculated as follows.

"Er"="real ripple voltage" X "temp sensor's resistance" / "(internal resistance in the ECU + temp sensor's resistance)"

The "real ripple voltage" is calculated as follow.
"real ripple voltage"= "Er" / "temp sensor's resistance" / "(internal resistance in the ECU + temp sensor's resistance)"

Roughly speaking the "real ripple voltage" is about 25% bigger than "Er" when engine is cold. It is several times bigger than "Er" when engine is fully warmed up because the "temp sensor's resistance" varies depending on the engine temperature.

My 98 Celsior's capacitors were all replaced already as a preventive measure and the reading result was only 5.4mV when engine was cold.

Regarding the limit voltage, see the post # 218. Those values are when measured by an oscilloscope and are the peak to peak voltage at the removed connector terminal of the coolant temp sensor. Most of good multimeters show the RMS value. Also the "Er" is smaller than the "real ripple voltage". With these factors, I'd say the read out voltage by a good multimeter when cold is preferred less than 40mV RMS. (RMS stands for Root Mean Square) Higher than 40mV RMS may cause intermittent problem.

 

Thank you for the very helpful information Yamae, glad to hear from you along with LSCowboy on my issue.

I will stop off at my local Radio Shack and pick up a capacitor and see what my meter says. I'm pretty sure I need caps either way since my car sat most of it's life before I bought it (149K miles on a 1994) and I don't think sitting in the hot weather would help the ECU issue much.

 

never posted results, but i cracked my ecu open, found this and desoldered and resoldered new capacitors in. haven't had a problem since then(knock on wood)

 

Thanks for the report with a clear photo.

I have questions. Was that the only capacitor leaking in your ECU? What about others?
What kind of failures did you have before the replacement?

 

yamae is correct, you need to replace ALL of those brown Nichicon PF(M) capacitors, anywhere from 6 to 10 of them depending on the year of your LS400, because eventually the other ones will start leaking as well, and it won't take long!

be sure to please use the caps linked to in the first post of this thread in order for the fix to work correctly!

 

sorry i didn't specify. I replaced all 6 capacitors (car is a 95) in the ecu. This was the only one that actually "popped" with the liquid leaking out. i read this thread pretty thoroughly to be sure this was the issue and went ahead and fixed it in December.
Since i haven't had any issues. The issues before were pretty bad, car would start sputtering to a stop and then wouldnt completely start back up for at least a half hour to an hour. If the car didnt sputter till the motor complete cut it would go into a "limp mode" or a fail safe. Which would drop into 3rd gear no matter at a stop/idle or at 60, ac would cut off, sometimes lights would cut, speedo and odometer would cut off.
It would stop after i would cut the car off and let it sit for a period of time, but figured out it was electrical after it randomly cut back to normal when was looking at it. Then i found this thread and all was better!

 

Thanks for the detail, flmadness.
Your report will be helping others who suffer strange problems caused by the ECU. Allow me to summarize the symptoms as follows, please.

Engine sputters to a stop.
No start back up for 0.5 to 1 hour.
Goes into a "limp mode" or a fail safe.
Drops into 3rd gear no matter at a stop/idle or at 60.
AC cuts off.
Sometimes lights cut, speedo and odometer cut off.
Problems would stop after cutting the car off and let it sit for a period of time.

After replacing 6 capacitors above problems were all gone.

I am glad that you succeeded to fix your car. Enjoy driving your LS400.

 

I have opened hundreds of "rebuilt" ECU's - exactly NONE of them had the correct premium Japanese low-ESR capacitors as linked to in post #1 of this thread.

so rebuilt usually means a hack job using inferior cheap and incorrect components!

 

Original thread HERE

So, after I've tried everything to fix the car, it still wasn't fixed and i decided to open up the ECU and see if I have leaking caps. Well, what do you know I do have leaking caps, so I ordered the right caps per the instructions in here.

Replaced caps and now all of my issues are gone. With the exception of my moon roof not functioning right. Here are pics of leaked caps.



This one has the most leak out of all of my caps. And actually out of 6 caps, only 4 seemed to have corrosion and leaked. The other 2 seemed fine but i went a head and replaced them anyway.



I wonder if that burned resistor at C110 will do any damage to the ECU down the road, i tried cleaning everything as much as i can.



Here we can see the corrosion.



This one seemed fine.



So is this one.



Another of the most damaged cap.

Replaced all the caps and everything is back to normal. Idles great without random misfire and car drives just like before. I wish I opened up the ECU earlier to check during my elimination process, and if it was fine I would've known that the ECU couldn't be the culprit.

I'd say if you're experiencing any kind similar problems that I had, open up the ECU just to make sure that it doesn't have leaked CAPS before throwing money / time at the car. All the parts i replaced were all original anyway so that benefit me so I wasn't wasting money since I planned to do all that soon. Now she's back on the road healthy again I can continue with my plans to make her better.

Thanks to LScowboyLS for this thread and help. And of course CL too.