I figured I'd post here since the SC400 has the same engine.

So my mom's 93 LS400 will not start. The car cranks hard and you can hear the starter trying but it just won't fire up. Also, when I take the key out I can still hear fuel moving in the engine bay and I can hear the fuel pump on in the trunk. I checked the EFI fuse and even swapped it out but it still won't start.

We just replace the battery but I still can't get it to start, not even by jumping it. Any ideals CL?

 

Plugs are too wet (from fuel). Maybe take them off and dry them out then give it another shot. At least dry out the #1 plug on each side.

 

I'll check that, but why would the fuel pump stay on indefinitely once I take out the key? This is what's draining my batter.

 

There is probably something wrong with the EFI main relay.

 

That's what my mechanic buddy said. Where is the EFI main relay and how can I check it? I looked in the owners manual and didn't see anything.

 

here you go... FYI, this is for SC's... Maybe the LS is in about the same location.

 

Ok I got the car to start by following the procedure in the owner's manual for starting a flooded engine. First I connected the battery in the LS to the battery in my SC and let it charge for a bit, then I got in the LS and tried to start it. At first it cranked but didn't fire up. I pressed down the gas peddle to the floor then turned the key and it fired right up and idled perfectly.

But there's still a major problem, the fuel pump stays on still when I turn the car off. I located the main EFI relay and swapped it with other relays but that didn't do anything. Also, I tried unplugging the fuel pump ECU in the trunk to see if that would turn off the pump but it didn't.

So basically there is a relay somewhere that is giving power to the fuel pump even though the car is off... and it's not the EFI relay.

 

so, its always "ON" even when the car is off? "ON" for how long? Till the battery dies? I also would have thought that when you unplug the fuel pump ECU that the pump will shut off immediately.... Are you the first owner? Maybe previous owner mess with the wiring and wanted it constant? Maybe there is an on/off switch somewhere and he bypass the ECU completely?

At least you got it fired up now... just a matter of troubleshooting the fuel pump from turning it off.

 

Ya the pump stays on until the battery dies or until I pull the EFI fuse or EFI relay. The EFI fuse and EFI relay are fine though, I swapped both of them out.

I am not the first owner but I know that the fuel pump has not always been constant, this is a recent thing.

 

I'm still trying to figure out why the fuel pump does not turn off when you unplug the fuel pump ECU. That module seems to have been bypassed. You said it just started recently??? hhmmm I suppose you need to check all the connections, grounding....

When you disconnected the fuel pump ECU, the fuel pump should turn off... It does not make sense why it is still on but its off when the fuse or relay has been disconnected... There is a short somewhere over there

 

Here's something you can check. Maybe it is the fuel pump ECU.

 

So I thought I had fixed it but something new happened today. While I was driving, slowing down to a stop sign, the car died. It wasn't a loss of power, just a loss of fuel.

The good news is that the fuel pump does not stay on anymore when the car is off so the battery isn't being drained. The bad news is it has never died while running before and it won't start even when jumped.

My buddy thinks it's a bad ECU, any ideas?

 

Will a 91 LS400 ECU work in the 93 LS400?