1995 lexus ls400 not wanting to stay running

[justafurr]

I have a 1995 Lexus ls400 that for the life of me don't know whats going on. about 7 months ago i had my ecu fail, luckily when i went to the junk yard i found an ecu with matching numbers that was already rebuilt (by denso) swapped it in and off to the races or so i thought. about at the 2 month mark of this new ecu the car just died on me. so i thought it might have been the ecu again. asked a buddy of mine that also has an ls400 for his ecu as a loaner to see if the car will run but that didnt help. No CEL light on at all. already replaced the cam sensors. crank sensor, fuel pump, relays, fuses. you name it I've probably replaced it. and the car still doesn't want to stay running. I called up Lexus to see if possibly my car has the immo but the said my car didn't come with immo. i can keep it running on starting fluid but after that it just dies, it has good fuel pressure at 40 psi cranking, the car will fire up for a about 5 seconds before shutting off. I've done testing to make sure it isn't losing a sensor while its running and all signals are present, the ecu seems to be cutting the injectors after start up (tested with noid light). honestly love the car and would hate to get rid of it. if there is someone that might know whats going on please help out

 

[Zuffen]

When I first had my conversion running about 20 years ago I had a similar issue.

I tracked it down the the fuel pump turning off as soon as the engine started.

The problem was the fuel resistor (it was a Crown engine) was faulty. Bypassed it and it ran well,

I now run a Soarer engine and don't use the fuel computer and it just runs the pump fast all the time with a tachometric relay to ensure it stops pumping if the engine stops..

I'd try fitting a temporary power supply to the fuel pump and see what happens. You could have a faulty fuel computer and I'm pretty sure it doesn't throw a fault code.

 

[justafurr]

my version didnt come with a fuel pump ecu just the resister. tried bypassing it and even putting power directly to the pump and samething

When I first had my conversion running about 20 years ago I had a similar issue.

I tracked it down the the fuel pump turning off as soon as the engine started.

The problem was the fuel resistor (it was a Crown engine) was faulty. Bypassed it and it ran well,

I now run a Soarer engine and don't use the fuel computer and it just runs the pump fast all the time with a tachometric relay to ensure it stops pumping if the engine stops..

I'd try fitting a temporary power supply to the fuel pump and see what happens. You could have a faulty fuel computer and I'm pretty sure it doesn't throw a fault code.

 

[Zuffen]

When the engine stops, does it still have fuel pressure. Crack a union to see if fuel squirts out.

Normally these shut down the injectors if they have an ignition problem, but this is the reverse.

I'd be confirming there is fuel at the injectors whilst it is running on spray and after. If there was I would suspect a poor power supply to the injectors. It's unlikely all four ground drivers would fail at once.