HELP! LS400 dies at start-up!

[pongoo]

I recently picked up a 1990 LS400.

the car starts and then immediately dies. but if u hold the key in the start position it fires and idles. is that just the cold start injector fueling the whole motor? I did a search and came up with the injectors could be clogged with gummed up fuel. I cant see every injector being that clogged, although the car did sit for 1 year. I was wondering what other possibilities it could be.


the car was missing its ecu so i grabbed one out of the junkyard. my car has traction control but the car that i got the ecu from didnt have it, could this be my issue if the ecu's are different? Also I found a thread about California cars having a separate ecu for the fuel pump. i traced the wiring in my car and didnt find a ecu for the fuel pump but the car i grabbed the main ecu from may have had one. Are the main ecu's different between California and 49 state cars?

Thanks in advance!!!

 

[Lextreme II]

I would also check the maf.

 

[spf_lexus]

Like David said, a bad MAF will fire up but will fall flat on it's face. Interesting about holding the ignition position... you dont get the metallic squeal from the starter? Just to rule out the computer I would start by getting an EXACT ECU match for your year and trim level. This will eliminate one can of worms. Very doubtful ALL the injectors are clogged but i guess you could get them re-balanced to rule that out also. If your really sure the cold start injector is causing issues, pull the manifold off and unplug it and try re-starting. It should not be required to start the car unless your in colorado like me where my LS sees 0 degree mornings.

Keep us posted, good luck.

 

[pongoo]

Thanks for all the replies I'll head out to the junkyard and grab a dfferent ecu. Today I took the intake off and cleaned the injectors. I haven't gotten it back together yet to see if that helps.

 

[Lextreme II]

You can test all of your igintion system before buying. There is a thread i posted on testing them. Another way to test if it is a fuel issue would be spray some carb cleaner into the manifold via the vacuum opening in the front of the intake. Have a friend start the car while u spray. If it starts and run, than it would be a fuel and possible ecu related issue.

 

[pongoo]

Ok so I cleaned all the injectors and changed the ecu to the correct one with traction control. I still have the same issue. It seems as if the ignition isn't holding for some reason. Any other ideas? Thanks again

 

[pongoo]

I also can't seem to find the thread for the ignition tests if simone could link it for me that would be great.
Thanks

 

[sideshow]

STA pin does jack pooo

just adjusts timign when cranking and might even do fuel enrichment including the cold start injecotr

test for injector pulse
if you have ignitor problem then yr injectors wont fire aswell
anyway u basically told us what is wrong now just find a way to test it

engine starts when cranking means running on cold start liek u said thru the circuit opening relay
so this means yr fuel system is ok

so either stuffed inejctors
no power to injectors
or ignitor/ecu problem which is disabling injectors because the ecu is in limp mode and doesnt want to flood the cylinders by runnign the injectors
check for error codes either 13 or 14 i think

 

[pongoo]

ive double checked every injector to clean and make sure the gates are opening and closing. and as of today ive tested for injector pulse.... theres power to the plug but no pulse to open\close them. do the igniters have to be matched to the ecu to function? what would cause the ecu to go into "limp" mode?

 

[pongoo]

ive also changed the fuel pump just to get it out of the way..... im totally lost on what to look for....

 

[sideshow]

check for codes
u will prob get code 14
if u do search the net for what it means

 

[sideshow]

thats not always the go

you see alot of ecus will not fire the injectors if there is no spark
this is so u dont hydraulic look an engine due to too much fuel going into cylinders
when there is no spark

basically ecu fires ignitors
ignitors fires coils
ignitors send signal back to ecu say hey i just fired coil
ecu say ok cool dude ill fire the injectors

99% of toyota ecus work this way
so u need to check for codes if u get any diagnostic code from 10 to 14
then u need to check this
its not to hard u just need an led testlight which can read pulses
then work yr way thru the signal line

i just stuffed around for 5 hours on a cressida with 7mgte and it would not fire injectors
spark was ok on 1 coil but not on the 2 other coils
this was because the return signal was not there
so as u can see this return signal is crucial to to the ecu so it can fire the next step

sta signal will not effect the running
the ecu knows that engine is turning
why do u think they fitted a crank sensor and 2 cam sensors
i can easily start a 1uz with no tps or air flow or coolant sensor

but without the ignition system working correctly u might get some spark but no injection

anyway yr wasting yr time until u check for codes

 

[Thermactor]

I recently picked up a 1990 LS400.

the car starts and then immediately dies. but if u hold the key in the start position it fires and idles. is that just the cold start injector fueling the whole motor? I did a search and came up with the injectors could be clogged with gummed up fuel. I cant see every injector being that clogged, although the car did sit for 1 year. I was wondering what other possibilities it could be.


the car was missing its ecu so i grabbed one out of the junkyard. my car has traction control but the car that i got the ecu from didnt have it, could this be my issue if the ecu's are different? Also I found a thread about California cars having a separate ecu for the fuel pump. i traced the wiring in my car and didnt find a ecu for the fuel pump but the car i grabbed the main ecu from may have had one. Are the main ecu's different between California and 49 state cars?

Thanks in advance!!!

Based off of what I've learned from UCF20 models:
1) I thought that all ECUs had a separate fuel pump ECU, not just Cali models.
2) I haven't seen any difference in ECUs between TRAC and non-TRAC models
3) California cars don't appear to have any additional sensors or anything - just different fuel and timing for emissions purposes, and an additional catalytic converter instead of a resonator.

 

[Supra510]

I'm having the exact issue, right down to the fact that if you hold the key in the position to start the car, it will run. It will even rev up if you press on the gas. But as soon as you release the key it dies. I've replaced the coils and sent the ecu in for repair/testing. Neither helped. I pulled the codes and I'm getting both 14 and 15 which is ignition signal.

Was there ever any resolution for the OP?

 

[Zuffen]

Your fuel pump drops from hi speed to lo once the engine starts.

If the fuel pump ECU is faulty it will stall if the lo speed circuit it faulty.

 

[Supra510]

Your fuel pump drops from hi speed to lo once the engine starts.

If the fuel pump ECU is faulty it will stall if the lo speed circuit it faulty.

I've already done the 12V bypass of the fuel pump ecu. It was the first thing I check actually. Unfortunately that wasn't it.

 

[gloverman]

In my experience these are the symptoms of something wrong with the ignition system like a stuffed coil or cam sensor faults. The last two I have done have had internal faults with the ECU - they had clearly burnt parts on the boards.

 

[sideshow]

easiest way to determine if its fuel or spark

spray carby clean or something flamable down the throttle body then start motor
if it keeps running its fuel related
if it stops then its more spark or ecu wiring or ecu related

if car starts then stops afew seconds later then most should be fine
fit a fuel press gauge to it also that will tell u what fuel is doing

but first test i ever do if motor wont run is put yr own fuel down it and if it keeps running
then its fuel system related
how did u do 12v bypass
maybe u made mistake run 12v from battery direct to fuel pump connector
this way theres no mistakes then work your way back from there

 

[Supra510]

It runs!! Pulled off the left front wheel as I was going to check the main battery ground . Looked up in the wheel well (yes, car is lowered) and the small black/orange wire was broken from rubbing. Soldered a new wire. Voila'

I thought it might be the wiring after I did some more reading. The car would keep running with the key in the start position with the starter whirring away you could even rev it. After researching it appeared the IGF signal to the ECU was the culprit. Honestly not sure if the black/orange wire is the IGF, but it solved my problem.

Trying to be positive at least I took care of any possible coil/ecu issues 'til this thing drops dead. And the fuel pump ECU as well so if this thing takes a dump again it won't be for those reasons.

Good to have it back on the road.

 

[ak47prince]

igf?

I taught the small Blk/Org wire is the igsw? the Igf wire color could be different..