If it's 3 seconds or 5 seconds, it might be an inhibiting mode.

The intake air temperature sensor is built in the MAF.

 

im thinking 1-2 seconds max....like you only realize it started then died

 

My thoughts were the same. When I lost the keys to my 1997, I had to remove the immobilizer and when I went to start it again I had forgot to plug it back in. Car would start perfectly normally for exactly 3 seconds, I could rev it freely but it would immediately shut off and not start until the key was removed from the ignition and reinserted.

 

still no luck with the lexus 400 I have ordered a esr tester to test the capacitors in the ecm.....to be something simple wrong or would not fire up

 

1-2 seconds so probably not inhibiting mode but thank you all for your input........we can do this!!!

 

as of now still not running.......the other mechanic that had it for 6 months told me the car has the immobilation system on it....tag on door says 1995 title says 1996 ive been under impression these had no immobilzation circuitry

 

update....car ls400 1996 will run on propane.........i have replaced the computer with a known good one in which ever single number on the case matched!!!! results the same fires up shuts off.....thinking of a 1996 lexus barbeque!!!!

 

Just a post that I have reached this non-resolution with similar problem....

I am looking for Theory of Operation that might help explain the Circuit Opening Relay which seems to have the job of cutting off the Fuel Pump Power.

Need to know: WHY it the Circuit Opening Relay doing this? Is it the Same 4 Reasons that
@Yamae asserts will activate the "inhibit" mode to prevent motor damage?

What are those conditions? There are 4 below. When one or more of these are detected, the ECU stops the fuel supply opening the circuit opening relay.
1, No signal from the MAF for more than 3 seconds.
2, No signal from the crank position sensor for more than 5 seconds.
3, No signal from the cam position sensor for more than 5 seconds.
4, No IGF signal from the igniter for more than 3 seconds although the IGT signal is sent.

I am in the condition that if I jumper +B to FP in the Diagnostic Connector (which bypasses the Circuit Opening Relay) the motor starts for a few seconds.

So my thoughts are, the ECU is Unhappy about SOME SENSOR even before you crank the motor, and that is why the Circuit Opening Relay is preventing the Fuel Pump from running.

But I get NO CODES in this OBD 1 era dinosaur, sad to say. I DO have an Oscilloscope or two.... but it is unknown to me what signals should look like. Is this correct?

I wish
@kuality had some status update!

Anybody? Thanks!

 

It's kinda obvious that you need to test each sensor and figure out via scope which one is not producing a useable/correct waveform. According to what you said there are only those four possible issues so just go down the list and eliminate them.

Also you have already checked the ECU right?

 

Thanks, I agree with you ..... IF you make the leap from [CONDITIONS THAT TRIGGER INHIBIT ON A RUNNING ENGINE] are by design the same as [CONDITIONS THAT CAUSE FUEL PUMP DISABLEMENT BEFORE CRANKING].
I listed those 4 conditions because that's all I can find.. I am MORE THAN reluctant to make that leap though!

I assert that the decision to disable the fuel pump is being made statically, before cranking, and the damn ECU KNOWS what it finds unacceptable but WON'T TELL ME (throwing no codes).

When you say "Checked the ECU" do you mean something other than checking for codes?
My wording was a little ambiguous but when I said "I get NO CODES in this OBD 1 era dinosaur" but I meant I checked for codes using the E1-Te1 jumper and found none (fast flashing only).
Further, when I disconnect the MAF and go through the crank-run-inhibit drill, I then get the 24 and 31 codes as expected for missing MAF.

Stumbling forward!

 

If it's faulty, the 400s are known to have ECU hardware failures. Looks like you have eliminated one possible issue already, nice job and you know it's not the MAF

 

yeah mine still same issue.....quit on it but still waiting and watching this thread....one day i may take an interest in it again....it just makes no sense...i hope someone finds the answer and posts it here.....thanks

 

It seems to me that the answer lies within your past post. The intake air temperature sensor is a part of the MAF sensor. One of elements of it is working as a temperature sensor. I'd simply check the output voltage of the MAF sensor using an air compressor. The important points are the initial voltage when there is no air flow and how the voltage increases in accordance with the increased air flow.

This video might be useful for you to check.

 

I would start with changing the fuel filter.
then coils.

 

did both coils long ago when i started.....it may help this other guy i have good fuel pressure and but yes checked them thank you