dogwisper

iTrader: (3)

This is actually a very easy repair. It is located right under the glove compartment.

Just disconnect battery, remove glove compartment under cover(2 clips), pull back carpet to reveal plastic ECU protector, remove the 2 screws that hold the protector in place and there is the ECU. One nut holds the ECU in place once the ECU is removed there is just one bolt on the back of it holding the harness in place.
Quick clean and easy. I've got a 92 SC400 mine went bad a few years ago with 180,000 miles on it symptoms were very hard start, ran pig rich belching black smoke, no idle, thought I lost her. Took it to Lexus to confirm it was the ECU. They said $1,200 plus labor. Originally replaced with a junk yard unit which lasted another year. I had mine rebuilt last year with a lifetime warranty for around $100. It is a cheap fix, this is a critical component that fails and it gives you future piece of mind. These cars are very durable but given that many are over 20 years old even things that don't frequently fail will fail in a car with electronics at this age. I live in Florida so the heat may have played a role. My advice is fix it and no worries down the road. Good Luck. Pat

LScowboyLS

I have a very famous tutorial on the failing ECU capacitors here

and yes, SC400 is affected at epidemic proportions, I have personally seen this failure hundreds of times on SC400, especially lately, and especially in warmer and humid climates and cars that have sat parked for extended periods (like months)

SC300 is affected as well, but at a slightly lower frequency.

SC430 does not seem to be affected (yet)

Tam4511

iTrader: (9)

*Or a blown EFI fuse...

Ali SC3

iTrader: (10)

If you look in the 2jzge and 2jzgte repair manual (probably all of them including the v8's), the test for the ecu is one to check the light operation with Key on like RedPhoenix said earlier, and the second test is to heat up the ecu with a hairdryer and see if it causes any problems.

I would guess the hairdryer is to heat up the unit so any failing components would show up rather quickly.
Its funny because there is a diagram of an ecu being heated up with a hair dryer in the manual.
I was surprised the hairdryer did not have its own SST number.

Yamae

I don't find any hair dryer as an SST in the manual of a JDM Celsior neither. I don't neither find any tutorial to change those Nichicon electrolytic capacitors like a timing belt although they fail much earlier than the engine worn out.

We had this post below at the LS400 Forum recently from silos5 living in Tallin, Estonia, North East Europe where they have cooler climate.
Is there any one who suffers from the AT shift problem which can't be fixed mechanically here in SC400/300 forum?

GeorgeNVA

Long time reader, first time poster
Registered mainly to post in this topic
I don't own a V8 Lexus, but rather built a conversion vehicle using '2000 JDM 1UZ-FE vvti . ECU is 89661-50522 .

Since I first drove the car, it was occasionally stumbling at WOT and low RPM. Recently the effect developed into audible pinging when stumbling occurs. Tried 98 octane and injector/combustion chamber cleaning (let engine run on specialized liquid, bypassing car's fuel system) - that didn't fix the problem (other than piston tops shine now)

Diagnostic run shown fuel trims were within +-5% across all load/rev range which is acceptable, however ignition advance sometimes retarded too much, with lowest peak values as low as -10 degrees btdc. ECU visually looked mint from the inside, no signs of water, no signs of cap leak etc.

I sourced another JDM ECU (89661-50521) , it was also perfect condition visually, and replaced its caps just incase. Used cheap Panasonic Low ESR parts. That seemed to address the problem so far. What I noted immediately is that the pinging sound disappeared, and at WOT/low RPM there's no surge.

I live in Moscow, Russia so the climate isn't hot or too humid, however ECU is installed near heater and is usually exposed to temps as high as 45 C.

p/s I was inspired to try the caps trick in my own ECU after fixing customer's 1994 1jz-gte ECU. The caps there were definitely leaking, and the car had rough idle / no power.

I saved the caps from my ECU to check their parameters in future. Maybe I 'll be able to pinpoint one or two parts that are especially out of specs while the rest would be quite ok.

t2d2

iTrader: (8)

^^^ That answers my question from another thread, whether there are examples of ECUs gone bad without visual queues such as leaking capacitors. I really need to pick up a spare to test mine out...

GeorgeNVA

t2d2 - note there are other components in ECU that could fail without changes in visual appearance. Examples are coild / injector driver ICs (or , on some ECUs, individual transistors), and cracks in soldering of power drive components which are known to introduce various problems. For example, cars like RX300 may suffer from the soldering cracks, the fault usually shows up as rough engaging in transmission. Fixing the cracks is as easy as resoldering all the components that drive ECT solenoids.

p/s also note that spare ECU from a wrecker may have other issues, better find some known car to borrow ECU from / let it run on yours

t2d2

iTrader: (8)

Exactly why I don't have a spare yet. I'm not aware of anyone in the area to borrow one from, so I'll eventually have to buy one supposedly in good working order. My symptoms are that the car constantly returns to long cranking at start-up. Every time I make changes that seem to help, it's back to the long cranks a day or two later. It seems like the ECU has a hand in matters, returning to a chaotic condition each time... Other than that, everything is operating just fine.

I'm getting my new fuel pressure regulator today -- the last two arrived as the wrong part, so I ordered from a different place this time -- which is the #1 culprit I've yet to fully test. Fingers crossed that the ECU is eliminated from the suspect list...

GeorgeNVA

there's a number of reasons for too long cranking time
One of them being leaky injectors. They may fail in quite weird fashion, holding 3-4bar without single drop, but dripping under lower pressure (so there's always some fuel in intake manifold after leaving the car for some hours). Seriously leaking injectors usually can be detected as negative long term fuel trims at idle (say -15%).

Additionally, the trims affect open loop operation (including start-up) which may explain why the problem returns after some modification

You can shed some light onto your problem by trying to reset ECU before each attempt to start, and by pressurizing fuel system (run fuel pump for a couple seconds before cranking)

GeorgeNVA

p/s have to add something to my report on replacing the caps

the result was consistent within 2 days/ 150km after replacing suspected ECU with the serviced one. Then I had to leave the car at paint shop as planned, but I'll try to repeat the experiment on one or two 1uz vvti conversions showing similar problems.

To guarantee that I only change one thing at a time, I replaced ECU right after confirming the problem persists when using 98 octane, and ran engine with new ECU and remains of the fuel. The effect can't be explained by just resetting ECU (freshly installed unit is apparently in reset condition) because prior to replacing I tried disconnecting the battery for numerous times with little or no result.

Key symptoms that were cured - poor driveability in low rpm / large throttle opening, occasional surge, audible pinging. Max RPM / WOT was always ok.

t2d2

iTrader: (8)

Thanks for the comments. Leaky fuel injectors is something I looked into a few weeks back and have been really, really hoping I don't have to address... Sounds like a pretty time consuming item to get to and replace. I guess I would need access to a scan tool for measuring fuel trim?

I've reset the main ECU numerous times and tried both bypassing the fuel pump ECU and running the pump for various durations before cranking. There's no consistent pattern, just lots of brief improvements followed by settling back to the norm.

Rather than derail this thread, though, here's one I started two months ago (yikes, didn't realize it had been so long) that never got any replies:

https://www.clublexus.com/forums/sc-...esitation.html - my thread

Mtdave2

Crazy post. I looked at my box it all looks good. Never would have thought of this

eblick99

iTrader: (1)

ill have to email my local lexus dealer and ask if they service ecu capacitors.

GeorgeNVA

Never. Best thing they can is offering ECU replacement