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I began having the usual problems with the fuel pump ECU in my '93 SC300; rough starts, no starts, engine stalls. The fuel pump would not kick on (I can hear when it does). Since then, I have replaced the fuel pump, screen, and filter. No dice. Then I found the following diagram and instruction from this forum: http://www.supraforums.com.au/forum/...fuel-pump-mod/
I bought the Bosch relay, wired it and the Fuel ECU like so, only to get 0 result. The relay coil won't switch. I tested that the relay worked by taking it out of the car and hooking it up to a battery pack so it isn't a bad relay. I put my multimeter on the contacts and when I turned the key, only got voltage at the 12V wire. The orangish wire (85) on the far left of the Fuel ECU only puts out 12V when the contact was disconnected. Is it unusual for your switching source to get 0 volts when connected, but to show 12 volts when disconnected? It doesn't make sense to me.
My band-aid has been to employ the same wiring as in the diagram, but adding a jumper between the 12V source wire (87) and the Fuel Pump wire (30). This way, the fuel pump gets 12V but it is unreliable. Ignition does not always occur this way. My ground is good. My wiring is good. My instincts tell me to look into that orangish wire at 85, but I'm not sure how since I detect voltage at it, albeit only when it isn't connected to anything.
If your wire at 85 reads 12V and the relay doesn't switch when you connect it, you have insufficient current to energize the relay coil. The voltage dropping to 0 when connected would make me suspect the circuit in the fuel pump ECU that is intended to drive the fuel pump. (A bad relay ground would still show 12V at 85)
Your band aid bypasses the relay, so it's the same connection as linked to in post #1 of the supraforum thread. You can remove the relay and it will continue to function as it does now.
If your wire at 85 reads 12V and the relay doesn't switch when you connect it, you have insufficient current to energize the relay coil. The voltage dropping to 0 when connected would make me suspect the circuit in the fuel pump ECU that is intended to drive the fuel pump. (A bad relay ground would still show 12V at 85)
Your band aid bypasses the relay, so it's the same connection as linked to in post #1 of the supraforum thread. You can remove the relay and it will continue to function as it does now.
-Tim
Thanks for the input, Tsmith. I'm hoping the circuit inside the ECU itself isn't the case because if I replace that and it doesn't work, I might then have to consider the main ECU as my problem.
Can anyone else offer some advice before I pull the trigger on a used Fuel Pump ECU?
Effectively, that is exactly what RanD has done. The relay serves no function since 87 & 30 are shorted.
The reason for using the relay and turning it on with the fuel pump ECU is to prevent the pump from running when the engine is off.
Bypassed as it is now, the pump will run as long as the ignition is in the on position. If you're OK with that- just remove the relay, cap off the ECU wire going to 85 and connect the 12V wire directly to the fuel pump wire. This should not be unreliable.
11-27-17, 06:22 PM
Wiring Refined Fuel Pump ECU Mod
