View Full Version : no power to fuel pump during starting

07-26-2012, 09:48 PM
so ive finally gotten most of my electricals gremlins exterminated. but there seems to be one more thats giving me a hard time on my st165. right now, the car wont start. and theres no fuel pressure when i try to turn it over. and when taking a voltmeter to the blue plug in the trunk for the fuel pump, i get 0 volts when trying to start it. so when i jump the two ports on the diagnostics plug to turn on the fuel pump, i only get 7 volts to the pump (the pump does work, its a brand new TT supra fuel pump and i get pressure when i jump it on the diagnostics port)...i feel it may have something to do with the ignition switch as well.. because i always have a code 11. which is momentary interruption to the ecu, and when i start it (new battery, new starter, and starter relay mod) sometimes itll click and tweak out. my question here is, i would like to either test, or just replace ALL wires involved with the fuel pump. as well as the ones coming from the ignition switch area. does any one have any suggestions on this before i attempt it? or am i pretty much just stuck with looking up the fuel pump diagram and going from there? any input is appreciate, thanks! :D

07-26-2012, 09:54 PM
Seeing as how when you jump the terminal you get (some) voltage back there says that the wiring is somewhat ok. Resistance builds up over time, just do another relay like your starter relay and that'll get 12v to the pump all the time (using the old blue wire as the signal to open the relay).

Other than that, I have no clue :) I'm not an electrical guy. I would just add another relay because that supra pump likes power.

07-27-2012, 02:57 PM
You're using a 185 ECU?
What about the harness? Which one are you using? And which relays/AFM are you using?

07-31-2012, 06:45 AM
im using a 165 ecu, 165 afm, and 165 harness. now, i did the fuel pump relay mod and when jumping the terminals on the diagnostics plug, the fuel pump sees full voltage! awesome! only problem, is i dont get a signal to the original wire that goes to the fuel pump. so the relay doesnt turn on. i checked the voltage further upstream of the pump. and checked the blue wire with black stripes, all the way as far forward as the driver seat, where it goes into a yellow plug, down by the fuse area. and i was only seeing .2 volts. then i went to my fuse box, and theres a brown plug that the OE fuel pump power wire goes to, that goes to the bottom of the relay box. looks like it connects to the EFI main relay. anyways, when i turn the car over, i see full voltage there. so somewhere theres resistance...also, i jumped the fuel pump resistor to keep it in high mode and when i turn the car over, i dont see any volts going thru that. argh, so frustrating

08-04-2012, 05:01 AM
look for FC pin on your third ecu plug, and check for continuiety from ecu to your circuit opening relay.

08-06-2012, 02:44 AM
He doesn't have an FC pin in his ECU, it's in the AFM; he has an ST165 [FYI this is why I asked what ECU/wiring you're running; the ST165 and ST185 work differently in this case].
Most likely either your AFM or your Circuit Opening Relay [COR] are bad.

Inside your AFM is a switch that gets' closed when the AFM door opens. This switch allows current to flow through a coil inside the COR. When current flows through the coil inside the COR it closes a switch inside the COR. This switch closing allows current to flow to the Fuel Pump Relay. I think you know the circuit from there. :)
This circuit is a safety feature. If your engine stops running [like in a crash] the AFM closes, and this stops the fuel pump from running.

Your COR should be up against the ECU, OPPOSITE the firewall side. IIRC The connector is facing the passenger side.

At the AFM the circuit runs through pins 1 & 2. 1 Is green, 2 is white/black. With the key on you should have 12V at pin 1. Once the engine is running you should have 0V at pin 1 [can check with FP/B+ jumped/engine running]. You can also check for continuity with the AFM door open.
At the COR it runs through pins 2 & 4. 2 Is black/yellow, 4 is green [same wire as pin 1 at the ECU]. With the key on [engine off] 2 & 4 should both have 12V. With the engine running 2 should have 12V, 4 should have 0V.

There is one other thing.
When you try to start your engine the AFM isn't open yet, so the switch inside won't close, so no fuel.
To get around this problem there is a second coil inside the COR that gets power from the starter. This coil also closes the switch inside the COR.
So when you go to start the car the starter powers the second coil, allowing the fuel pump to turn on, then as the engine actually starts the AFM door opens and powers the first coil, keeping the fuel pump running. Once you turn the key back from start to on/run the starter no longer powers the second coil, but the first coil is now powered so the fuel pump keeps running.

Wiring for the second switch in the COR is pins 3[+] & 6. 3 Is black, 6 is white/black.
With the engine cranking pin 3 should have 12V, pin 6 0V. I'm not sure what the resistance is supposed to be, but you should have continuity across 3 & 6.

You can also jump the pins in the COR connector to verify.
You'll want to jump 3 & 6 to check the second coil, and pins 1 & 2 to check the first coil. Pin 1 is blue/orange.

I hope this helps. :)

08-06-2012, 02:46 AM
One other thing, I'm assuming your EFI relay is good, the COR gets power from it.
If you don't have 12V at pin2 of the COR the EFI relay [or EFI fuse] is probably bad.
And, just in case you don't know, there's also the possibility wiring or connector pins are bad too. But check the other stuff first. It's easier to rule out. :)