1UZ ECU - How specific are they to each engine/model - LS400/Celsior

[roadkill]

Hi All,

I have a 93 LS400 here that has a bucking/surging issue and i'm currently leaning towards it being an issue with the ECU. Now, so far i haven't been able to find anyone with the same part numbered ECU. I have an 89661-50180. I can get an 89661-50170 though to throw in and see if it is the ECU or something else. The pin setup is exactly the same on it and from everything that i can find the pin out is the same. So, if i swap this ECU in, do you think it'll run the engine and what differences could there be in it?

Any help is appreciated.

bEn

[CrUZida]

UCF10 and UCF11 will have different numbers, but should be compatible (UCF10 may not work in a UCF11...)
Likewise LS400 and Celsior will have different numbers as they'll be programmed for different fuels, but should be compatible. JDM stuff will also have speed cut at 180kph.

I say go for it.


Bucking/surging is unlikely ecu (in my opinion). Disconnect different things one at a time in the engine bay, and see if it helps. AFM, TPS, etc.
If something is faulty the surging will go away when you disconnect it.

[roadkill]

Hi,

cheers for the info. I never thought it would be anything to do with fuel but that def makes sense. I also have a celsior but it's a 90 model and has different pin setup. The ls400 doesn't have traction control which i think is the biggest difference between the celsior and the ls400.

So far i've tried swapping an another working TPS, disconnect AFM, EGR, Cam sensor one & two, Bypass fuel ecu, bypass fuel pressure reg (so it has full pressure all the time) am still yet to disconnect teh 02 sensors (there's 4 i think) and going to try to see if it is an ignitor/coil tonight (i really don't think it is) Most people with ls400's in the states that i've come across have had issues with the ECU but not all. For the sake of swapping one in to see if it'll work can't really hurt.

It does throw a TPS error but no CEL. That was the first thing that i swapped out and did the exact same thing. Everything that i have tried doesn't seem to change anything........

bEn

[CrUZida]

If its throwing a TPS error with 2 different TPS's then perhaps the wiring is corrupt?

The surging I've had in the past has been caused by the TPS going into IDL mode when you've been at light throttle (ie, the ecu thinks the throttle plate is closed), and it starts to open and close the ISCV causing the surge.

But, I suppose its possible that the ecu is the cause of it all.

[roadkill]

yeah that's another thing that i've gotta try yet too, but kinda hard to do by ones self. Prolly on the weekend i'll see what the continuity is when i have some extra hands.

That does make sense though from what you've said there. ECU thinks that the throttle is closed, so hence not enough fuel and seems like it is dying, then when the revs come back to near idle it picks up again......

Doesn't explain though why it runs perfectly fine it park......

bEn

[George]

roadkill, get pdf repair manual for the LS400 and see what it suggests for dealing with your error codes. http://www.ls400.ru/lexus-89-2000/index.html

I've done some 10 of UZ's so far (mostly JDM stuff though,1993-1999) and no one had any issues with ECU. LS400/ ucf10 ECU's should be interchangeable as long as they have similar connector configuration

[Cuzzo]

Leaky caps?

I'd be swapping the afm first.

[roadkill]

Hi,

i'll follow the diagnostic tomorrow after work. See if i can find a dead wire or something. The ECU that i have had two leaky caps, and another with green feet. We've replaced those three and no change.

What makes you suspect on the AFM? It's throwing a TPS code. Hence the tps was the first thing i swapped out....

bEn

[dumbass]

ive only got an ealry celcior ecu no 89661 50102
i had an 02 to 04 celcior ecu with chunky plugs 2 weeks ago from a customers job
but thats gone back to sydney with his loom

i would check the ecu capacitors and also wire up diagnostic plug and read live data
i do it all the time when theres issues since my scanner can read about 20 bits of data from toyotas,
as the early oval/rectangle diag plug ecus give pretty crappy live data so u need to know what to look for
when trying to diagnose

[roadkill]

Hi,

ok, so i had a little bit of time up my sleeve this afternoon to get into this again, and i didn't end up getting this other ECU so i have to keep diagnosing. Now, for the first time i've managed to get it to error in neutral. It only does it if i go WOT though. Quickly checking the diagnostics port found that the fuel pump goes up to 12 when initially WOT but then as soon as the revs die (roughly 4k) it drops back to 8v and stays there. The ignition circuit however goes to 0v! So, that to me says that the reason the revs are dropping off is there's no spark.

Now, why is the spark dropping out..... Can crappy igniters/coils do this? I should hopefully be able to get a spare pair of hands for saturday to test the tps to see if everything is connected properly there too

BTW replaced 3 caps in the ecu. 2 were leaking and one had green feet, so we assumed that it too was leaking or had leaked at some point. Everything else looked right

bEn

[dumbass]

what do u mean ignition circuit goes to 0v

the orangblack wire?

[roadkill]

Hmmm, will have to check the wite colour when i get home. I connected the IG terminal in the diagnostic port at the top of the engine to the earth. The IG is the one at the back left, kinda by itself and is the biggest one in there. Going to check others tomorrow to what also changes (if any)

bEn

[dumbass]

Ig- is tacho signal

Nothing to do with making car run rough
Be carefully what u ground out as u could fk things if u have no idea what they do
I could look at it if u want to pay someone
Otherwise maybe find someone else on here
Or bring it to powercruise this weekend I'll be fixing all the shitboxes heheheh

[roadkill]

Wow - thats silly. I will admit twas a guess as i didnt have time to look it up. All testing has been done with a multimeter, so should be safe......

Car isnt rego'd so cant take it anywhere. Got a mate coming over on the weekend to give me a hand so we'll see what we can find then. If we get stumped i may have to invest in your expertise.

In no hurry, just annoyed by its not running..... Worst case the engine comes out n the car gets junked....

bEn

[4th surf]

I have been thru this with an LS and also the Soarer 1UZ that is in my own Surf. With the LS we did throw a Celsior ECU in it and it ran fine even with the cost of the ECU and a bit of refreshment to it (which also removed the 180 cut out) this proved to be a good upgrade due to different fuel and ignition maps in the JDM Celsior. However the "bucking and surging" still remained. It had new leads, plugs, caps and rotors and the coils tested perfectly yet it still surged and gave some strange O2 readings with the scanner plugged in on live data both with the original ECU and the Celsior item. So one Saturday over a few beers we decided to give Repco a call and see how much new coils were as that was the only thing not changed. Two were in stock at a pretty good price. Collected and fitted along with a set of green top injectors. Problem solved.. It was "Sit down. Shut up and hang on". L/H coil was breaking down as soon as the engine warmed up so in effect it dropped 4 cyls intermittantly