Fuel pump ground?
05-03-12, 02:24 PM
#19
Ok, with more testing, I think I know what's going on. I attached a motor load across FP and FP- and the controller behaves as designed. The motor did not run until I applied 5v to FPC. Then the motor ran as expected.
The bad news is that it seems that I was correct in assuming that the GS pump is not grounded to chassis. At least I am 99% sure of it. If I ground the negative terminal of the motor to "chassis" as it is set up in the SC, the motor runs full bore regardless of FPC signal.
Bottom line is that I dont see how this thing will work on my car unless I do some crazy dangerous fuel pump rewiring.
The bad news is that it seems that I was correct in assuming that the GS pump is not grounded to chassis. At least I am 99% sure of it. If I ground the negative terminal of the motor to "chassis" as it is set up in the SC, the motor runs full bore regardless of FPC signal.
Bottom line is that I dont see how this thing will work on my car unless I do some crazy dangerous fuel pump rewiring.
05-03-12, 03:05 PM
#21
Which pin D are you talking about? If you are referring to pin DI, pin DI is just the diagnostics pin, and its sole purpose is to feed a signal back to the engine ECU. As long as the engine ECU sees signal incoming on DI, it will continue to control the fuel pump ECU via pin FPC. If nothing comes in on DI, the ECU assumes the fuel pump ecu is bad and will cut signal on FPC, effectively turning the fuel pump off.
The problem keeping me from using this fuel pump ecu on my SC is ground isolation at the pump itself. I know of one guy who made this controller work on an SC, but his car was a 98. I am not sure if the 98 SC is wired differently, or if he rewired his pump ground circuit. I'm going to PM him, but he has not really been active on here for the past 2 years so I have little hope of a response.
The problem keeping me from using this fuel pump ecu on my SC is ground isolation at the pump itself. I know of one guy who made this controller work on an SC, but his car was a 98. I am not sure if the 98 SC is wired differently, or if he rewired his pump ground circuit. I'm going to PM him, but he has not really been active on here for the past 2 years so I have little hope of a response.
05-03-12, 09:02 PM
#22
If PIN DI is the signal to the PCM and the FPC controls the fuel pump, E is grounded always. The fuel pump cannot be turned on unless key is in ON position. You are saying with the key is off the Fuel Pump is always running? Or the fuel pump is not working because you cant find a ground?
05-04-12, 08:31 AM
#23
Neither. When I turn the key to ON, the fuel pump runs. It stops when I turn the key OFF. IF I isolate the fuel pump ground from E, the fuel pump ecu will work as expected. The problem is that I CANT isolate the fuel pump ground from E unless I get really creative with the fuel pump hanger and the wiring at the pump. The SC was designed differently than the GS. The pump and its ground are bonded to chassis in a couple different spots, and isolating it would not be easy or really safe IMO. I think I may approach this differently and try to modify the FPC signal to trigger a Supra FPECU instead.
See how the SC bonds the pump to chassis? I have no clue how this other SC guy made his work. My curiosity is killing me.
See how the SC bonds the pump to chassis? I have no clue how this other SC guy made his work. My curiosity is killing me.
05-04-12, 09:35 AM
#25
That is the problem though. With the SC wiring, you can see that fuel pump negative is bonded to FP-, which means I am already grounding FP-. That is what causes the pump to run at full speed. By NOT grounding(bonding) FP-, the pump operates as it should and not wide open as soon as the key is turned to ON.
05-04-12, 10:45 PM
#26
The FPC is the one that controls the speed by sending a variable voltage depending on load, not the ground. The ground is just to complete the circuit. The Fuel Pump is controlled by the positive side, not ground. That's the realistic purpose of that system. Now since you are using a different ECU on a different car, maybe that's why it's not recognizing?
I think you got a bad signal wire for DI. Check that wire if it's shorted to ground.
Or try tapping the FP-, to the E Ground and see if it works differently. It's safe. Ground to Ground is fine.
I think you got a bad signal wire for DI. Check that wire if it's shorted to ground.
Or try tapping the FP-, to the E Ground and see if it works differently. It's safe. Ground to Ground is fine.
Last edited by GS4_Fiend; 05-04-12 at 10:49 PM.
05-05-12, 05:19 AM
#27
Trust me here. I have tested this thing extensively and I can make it work like it is supposed to on the bench. As long as I wire it exactly per the GS diagram I posted, everything works. No big surprise there. The problem is pump ground isolation. The SC wiring essentially attaches FP- to E, and that is the whole problem here.
As soon as I BREAK the connection between FP- and E, the pump works as it should through the fuel pump controller. DI does not make a bit of difference in my case because I am putting my own signal on FPC.
As soon as I BREAK the connection between FP- and E, the pump works as it should through the fuel pump controller. DI does not make a bit of difference in my case because I am putting my own signal on FPC.
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