joytech22

Hi guys,

As per the description, I have a 1995 made (1996 plated) LS400 and the thing is a rocket when cold but it is an absolute slug when it is warmed up - no CEL (OBD 1 model, Australian)
I replaced the ECT sensor to no avail, that really annoyed me making no change since it was a real pain.

It is horrendously slow when it is warm, I'm talking slow like can't keep up with a 1.8L Nissan Pulsar (or Sunny in some places).
The exhaust note changes too, it has a much more V8-ty sound cold than it does warm, WOT warm you don't really hear the engine until 4000RPM...

No surging/stalling/sputtering issues here, just lack of power.
FYI just so you guys don't jump down my throat, I don't WOT the thing after starting. I drive it 10 or so minutes sedately - that's "cold".

Warm is when it finally hits just over half way on temp gauge.


Any recommendations? MAF? O2? What could cause this?


Thanks in advance.

djamps

These years are notorious for bad ECU capacitors. This guy has same issue as you too:

https://www.clublexus.com/forums/ls-...nk-2-only.html

Mega thread:
https://www.clublexus.com/forums/ls-...capacitor.html

joytech22

I did read a lot of these bad cap threads, but my car isn't displaying any of the symptoms from the mega thread.
It runs fine, no CEL it's just slow as crap when the engine is at operating temperature - it doesn't even bog, it's like it loses 50HP throughout the RPM range.

I mean I can needlessly spend money fixing the caps on the ECU but I think that's just an unnecessary/complicated/expensive thing to do without additional troubleshooting.

Yamae

A smart guy would quickly check the ripple level to see the condition of ECU capacitors explained in the FAQ page.
https://www.clublexus.com/forums/ls-...-by-yamae.html

Anyway it's been 20 years and it sure is long enough for those QAS capacitors to loose the capability to work properly.

joytech22

Thanks for the feedback djamps/Yamae, sounds like you guys might be on track as much as I hate to admit it.
Uuuuughhh.... Always the expensive bits to break. I'll try and diagnose the ECU - Might just yank it out and take a look myself and do some measurements.

Lexus wanted $6000 for a steering rack and $1600 per shock assembly..

There's quite a bit wrong with the car, I was willing to fix the rest but this has pushed it over economic repair territory. I don't have the financial backing to invest this deep into DIY... Sydney's like the second most expensive city in the world to live lol

I'll try and get a quote for an electronics place to repair it (if I provide the caps).

djamps

Whatever you do don't be tempted to buy a used one online or from a junk yard as nearly all of them are either failing or close to it. If the ECU is the issue it's a relatively minor repair compared to other stuff as you've mentioned, as long as you can deal with the downtime. And lastly a dealer is the last place you want to get work done on an out of warranty vehicle (they call them stealerships for a reason here in the states).

GasBuggy

Just to give some helpful input. I had this same issue with my 94, and I rebult the ECU myself. That solved a lot of my problems but not my slow when hot issue. I changed the master temp sensor, it's green plastic and brass.

joytech22

I was going to do something similar, but buy an ECU from a junk yard and if it was not damaged by cap leakage recap it and use it in my own car.
The quotes from Lexus were just for the part, not the work lol.

What is that? I replaced the coolant temp sensor but that's it so far. Is that what you meant? The replacement had a plastic green connector but the original had a brown one. Replacement apparently reports to the ECU in the same temp range.

joytech22

Just an update, I have purchased the capacitors and am waiting for them to come in.
I have a work friend who is a technician and will help me install them (as I have a $10 soldering iron and minimal experience).

GasBuggy

You replaced the correct sensor. In that case new capacitors will probably work.

joytech22

A quick update, I had all caps replaced - car is now as good off the line as it was when cold and pulls strongly to redline.
I suppose I expected my LS400 to be as fast as my Falcon G6E, same engine size at 4L but inline 6 with more power/torque - just goes to show how far technology has advanced.

I'll definitely miss my usual off-the-line advantage when I drive the Lexus compared to my G6E

jaaa

Cost me $12 to fix the caps on two ECU's. I wouldn't call that expensive.

joytech22

It gets expensive when you begin investing in the tooling required to do every little job.

I have the soldering iron but not the tips or skill, so palmed it off to a friend to do for some cash.

Also caps cost me $70, first batch was from the US and was incorrect since they have different ECUs to Aussie models so had to buy locally. Labor $100.

dicer

So Yamae should get a gold star on this one, he was right on.

joytech22

djamps/Yamae both deserve kudos, not sure if this site has a reputation system to rate them or best answer but I thank all involved.