1993 LS400 gearbox issues?

[roadkill]

Hi All,
I have a 1993 LS400 and when in park or neutral the engine revs fine, will red line etc and has great response and runs as it should. But once put in gear its horrible. It misses, revs drop etc from about 1500rpm onwards. The speedo doesn't work either but i think that might be a separate issue. If i ease the throttle on slowly it will rev up kinda ok, but it's still pretty ordinary. Even a granny would put their foot down harder. I'm thinking it's either gearbox issues or the ecu not communicating to one another well. Any ideas?

Any help is appreciated,

bEn

[dumbass]

fix speedo problem first
see what that cures

[4th surf]

Drive the car and see if the odometer still ticks over. if it does then the VSS is still working but if not then you've found the problem so as has been posted above.

It may also be an idea to check for codes as sometimes they will log them and not bring up either the check engine lamp or O/D "flash" so connect TE1 to E1 in the diagnosis plug and see what flashes up. For engine you are looking at the check engine lamp and trans the O/D lamp. O/D switch on the shifter must be in the "on" position. If there are no codes both lamps will flash constantly

[dumbass]

u could also try remove all electrical plugs from auto
manaully change gears with the gear shifter
u wont get all gears but will give u good idea if its mechanical or electrical
friend has ls400 with similar problem at yatala which i looked at for him
he has fkt gbox

[roadkill]

Hi,

so I took this for a better drive today and it turns out the speedo DOES work. The trip meter works too. So theres nothing wrong there. I think that i just hadn't had it quick enough to jump up over 20. So anyway, just went and check the diagnostics and it threw out error code 41 which is a throttle position sensor. I'll swap in the one from my celsior and see what happens!

bEn

[roadkill]

Hi,

so, the celsior one is different as the lexus is a 93 and the celsior is a 90 model. Anybody got a 93/94 lexus tps i can borrow to see if it is indeed the tps? I'm kinda hoping that it is. By the looks of it too, there's a camry that has the same TPS Alternatively, does anybody know how to test if the TPS is shagged or not?

Food for though - i cleared the engine codes. Re-started it and it def had no codes. Let it run, revved it up and everything in park and was fine. Slip it into gear, go to drive and it gets to about 1500rpm with a bit of the right foot into it and it starts doing the same thing.

bEn

[roadkill]

Hi,

so got a TPS and swapped it over, but it does the exact same thing. So that rules out the actual sensor, but there's nothing to say that it isn't the wiring either side of it.

I have done some more reading as i'm trying to think of other things in the system that it could be and i've come up with one quite likely potential problem. The fuel pump! According to everything that i've found the fuel pump runs at two different voltages. One (lower voltage) for idle/low fuel consumption and 12v for when the engine is running under load. This is controlled via a relay that has an input from the ecu to make it run through a resistor dropping the voltage. This leads me to the potential that when it is supposed to be operating at the full 12v it simply isn't getting the power, fuel pressure drops and so hence the car doesn't accelerate. My question is, does anyone know where this relay is located? If i can locate this relay i can see if it has signal etc and go from there. I also have a ucf11 celsior and i've found it there (near the abs module behind the drivers headlight) but on the ls400 it doesn't have it there! I have no idea where it is so help is appreciated.

I plan on getting it up on the jack stands on the weekend and disconnecting the electrics from the auto and seeing if that changes anything. Just hoping the fuel pump idea is the winner!

bEn

[dumbass]

i doubt the fuel pump low voltage will cause issues
they change to hi voltage at 4000 rpm
the engine ecu controls thre auto too
i have a jap spec celsior ecu if u want to try if u come round and fit it

maybe pull yr ecu apart and check the capacitors

[roadkill]

Hi,

hmmm, bugger. Just from what i'd read the ecu changes the voltage on the fuel pump dependant on load. If i light foot it i can get to 3-4k revs (changes gear then) but heavier and it starts to accelerate a bit harder and it just won't do anything. Coughs and splurts. Was just thinking of bypassing the lower voltage and have it have a constant 12v when ignition is on. Worth a shot.

That'd be cool if i could try the jap celsior ecu. I've got a celsior here too but it's a 90 model, the ls400 is a late 93 so from what i can gather theres a few little differences. But i can always try it n see. Also, the ls400 doesn't have trc, but the celsior does.

Whereabouts are you located?

bEn

[roadkill]

Hi All,

ok so i spent more of today trying to diagnose what is going on here. I did ALOT of reading on the interwebs last night and found a few similar cases but none of their theories have worked for me so far. I've tried;

Disconnect fuel pressure reg - constant pump controlled pressure
disconnet afm - gets the ecu to run base tune
disconnect egr - make the exhaust gas not go through the engine
clean out fuel pump - duh
re-routed the power for the fuel pump to be 12v constant and not stepped down for low revs

swapped another tps - and this is where i'm at now! So, i thought that i'd muck around with the tps, see if it was just not quite properly aligned. But something has struck me as odd. Regardless of where the tps sits the revs stay the same - ~650rpm. I tested the tps on my celsior and the revs go up/down according to the direction that you twist it. SO, this brings me to the conclusion that the tps's signal is either not getting to the ecu or that the ecu isn't using the signal. Now, does anyone know where i can get the pinouts for the ecu for where those wires are supposed to run to? So i can see if there is continuity through them or not? If there is continuity then the only thing that i can see is that the ecu is shagged. So if someone has one that i can borrow that'd be fricken schweet!

I still haven't tried the gearbox disconnect cables thing yet as i haven't had time jack it up and get at those connectors. EVERY single example i found on the webs last night had similar issues and not one had anything to do with the gearbox. So that's probably going to be my last resort.

Many thanks,

bEn

[dumbass]

i dont know y people just go hell for leather changing sensors
get a multimeter
porbe the tps
if u get anywhere around half a volt at idle and slowly going up to 4 volts at full throttle then its fine
it seriously much quicker than changing it

[roadkill]

Lol - sounds good. I'll check it when i get home tonight. As for replacing the tps it was cheap n easy, and more to the point i didnt know how to test the tps at the time. My celsior has now benefitted from previous said tps. Ls400 is still poo. Do you know where those signals from the tps run to on the ecu? I want to check for continuity in them to make sure theyre sending the signal to the ecu. Replacing a wire if broken is cheaper than an ecu :-)

bEn

[dumbass]

its prob 5% chance of broken wire in a std untouched car

toyotas are pretty good

[roadkill]

If its not a broken wire, then its prob a broken ecu..... Will hopefully confirm this tonight!

[dumbass]

look at wires on tps
one is brown on one end of plug
next one is idle next one is tps signal final one is 5v
test signal one at tps with ign on and plug plugged into tps

then remember the wire colour and go find same coloured wire at ecu
and test same voltage
if there is more than one wire with same colour try em all
or get wiring diagram and find the "vta"