Fuel pump won't work - but works when 12V applied from battery.

[EIL_V8]

Hi again guys, I have another problem with my UZZ31 if you could lend some advice.

Here's the issue: (Updated).

One day the car refused to fire. Cranks but won't fire.
No fuel delivery.

Swapping the main relay with the dimmer relay does nothing. Other fuses seem good in engine bay...
Applying a cable from battery directly to fuel pump allows car to fire and stay running.

It should also be noted the car has new plugs, wires, coils, distributors, timing belt, water pump, and so on. Everything but the ignition control modules on passenger side (JDM) of engine bay near fuse box are new.

I have the car rigged from Positive battery, to a fuse, to a switch in the cabin, to fuel pump behind rear seat.

Does anyone have any ideas what is going on?
Bridging +B and FP does not allow fuel pump to work when key is turned.
Only applying 12v lets fuel pump run.

Also, my diagnostic dashboard codes are not working for EFI and ECT, they come up as - -.
We've tried 3 different ECU's now, no codes on any. Codes work on other cars.


I am running a Crown 1uzfe ecu apparently, perhaps that has something to do with it...
I am running a "31" ecu from a newer Soarer allegedly.
Fuel pump issue existed with original uzz31 ecu also, it was actually swapped because of it, but never fixed issue.

Thank you!

 

[numbchux]

Bridging +B and FP does not allow fuel pump to work when key is turned.

I would start here. Do you have battery voltage to B+? If it does, I'd check continuity between FP, and the output from the fuel pump controller, and the pump itself.

 

[EIL_V8]

Hey thanks Numbchux.

I'll buy a meter today and check, but from memory a while back there was no +B, or +B was half the voltage?
I may be wrong.

I have swapped 3 ECU's, all have same symptom.
+B and FP doesnt let fuel pump run. Only wire from battery does.

Fuel pump is original to my knowledge, it's time it failed.
But can it fail in a way that it won't work when key is turned, but will still work when 12v is applied from battery?

If no +B at diag port, what to check?

Thanks!

 

[blackdemon_tt]

Have you bypassed the fuel ECU in the back seat? I jumped mine and would work fine but then stalls and hard starts returned so I replaced fuel relays and reconnected the fuel ECU, its been a week on this trial and error so far so good.

Side note, don't drive with the jump, I did and the jump wire got fried and left me stranded. Damn near caught my car on fire too... if you must bypass the fuelECU have some one clip and solder the bypass with heat shrink protection.. otherwise trial and error with both relays and you may be lucky and not need the bypass..

 

[Zuffen]

Some Crowns don't use a fuel ECU. They have a large resistor that drops the voltage to the fuel pump.

When starting the fuel pump is in high speed mode and drops to low almost immediately (say 3 seconds) and this may be your problem.

If you don't have the resistor in circuit it may not supply power the the pump after start up.

Don't drive the car with the fuel pump "hotwired" as the pump won't turn off in an accident

 

[EIL_V8]

Have you bypassed the fuel ECU in the back seat? I jumped mine and would work fine but then stalls and hard starts returned so I replaced fuel relays and reconnected the fuel ECU, its been a week on this trial and error so far so good.

Side note, don't drive with the jump, I did and the jump wire got fried and left me stranded. Damn near caught my car on fire too... if you must bypass the fuelECU have some one clip and solder the bypass with heat shrink protection.. otherwise trial and error with both relays and you may be lucky and not need the bypass..

Fuel ECU is still plugged in, but the cable from the battery in engine bay (to switch in cabin, then to fuel pump in back seat) provides 12v and allows the car to fire and idle. So the wire from battery bypasses relays or what not, providing power straight to fuel pump as I understand.

Now, what I noticed is that usually when I flick fuel pump switch off, the car cuts out as there is no fuel. But sometimes (1 in 20 times), if I flick the switch off the car will stay running as the fuel pump is getting power again. But then if I turn car off and on - it won't fire up again unless I turn the switch on.

I've changed the silver round relay with the other one in the engine bay fuse box and same condition. Fuses appear good.

I have "engine electrical error" on dash, but no codes.
I also have a low idle which may be related (same with 2 ecu's). (Goes to 400rpm in "D" and sometimes stalls when playing up. Or might rev to 1500rpm in park, but 800 in D, then after 10 mins driving goes to 400 in D and may or may not stall).




Thanks!

 

[EIL_V8]

Some Crowns don't use a fuel ECU. They have a large resistor that drops the voltage to the fuel pump.

When starting the fuel pump is in high speed mode and drops to low almost immediately (say 3 seconds) and this may be your problem.

If you don't have the resistor in circuit it may not supply power the the pump after start up.

Don't drive the car with the fuel pump "hotwired" as the pump won't turn off in an accident

That's good info!

The fuel pump not working issue happened with the UZZ31 (29) ECU, and that is why it now has a (31) crown ECU (or something). The ECU looked good to me aside from bad caps, but I was told it was bad and to swap with his one. I may have been scammed seeing as how this fuel pump issue happens with all ECU's, so it wasn't the ECU at all.
It did fix my idle rolling up and down (bouncing off at 2000rpm over and over).

Thanks for the heads up though.

 

[EIL_V8]

Still wondering what the issue could be?

I have recently found out I have a hydro fan leak...