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indy-tech, Australia Car Mechanic
Category: Australia Car
Satisfied Customers: 7065
Experience:  All import and domestic car repairs and diagnostics
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I have found the fuel pump control unit but trying to work

Customer Question

I have found the fuel pump control unit but trying to work out which colour wire is the PWM (FPC) on my SC400 (1991) Sorry my name is ***** ***** Kilby]
JA: Thanks. Can you give me any more details about your issue?
Customer: If I connect the fuel pump to B+ the fuel pump runs at full power (noisy) but car starts and gives dark grey smoke
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Submitted: 1 year ago.
Category: Australia Car
Customer: replied 1 year ago.
I have some info here:
Customer: replied 1 year ago.
It doesn't have colours on the pinouts for the wires. Just codes like B+ (battery 12v) FPC, Di (sends 12v back to to tell ecu is working) I think one may be earth, so that is 5 pins
->B (12v)
<-fuel pump
Expert:  indy-tech replied 1 year ago.

If you can energize the Fuel pump with the jumping the B+ in the DLC 2 then check the EFI main opening relay .

Or have you tested this relay .


Customer: replied 1 year ago.
The fuel pump runs with B+ no problems albeit at full power. I need to keep the variable fuel pump rate.
Customer: replied 1 year ago.
If I can work out what wire does what. At least if I can find out which wire is the pulse width modulation, I can make up my own circuit to regulate the power going to the fuel pump.
Expert:  indy-tech replied 1 year ago.

Here is the diagram of the fuel system .

Hope this is what you need .

Check the fuel pump ECU

Print and stick together as one sheet in two parts .

Rgds Greg

Customer: replied 1 year ago.
Ok so now I know what PWM is, how do I check to see if PWM is working? Do I use AC on an analogue meter? Or do I use a digital meter on AC?
Expert:  indy-tech replied 1 year ago.

Kilby PMW do not read or speak Analog, only digital .

What you trying to test .

Check the connections and wiring to the Fuel pump ECU if you have the pump working then you are not getting power from your FP ECU.

Rgds Greg

Customer: replied 1 year ago.
Fuel pump works. If the fuel pump controller isn't getting a pwm signal, then basically it won't turn on the pump. So that's why I want to check the pwm signal. But how?
Expert:  indy-tech replied 1 year ago.

Do you have power at pin 6 green wire (Fuel pump ECU) when cranking the engine .This is power to the fuel pump when cranking ;

No power , check the voltage at the FPC red / green wire..if no power from the ECU then you have a bad ECU


Customer: replied 1 year ago.
There is no PWM coming from the red/green line. But when I connect the OBD scan tool to the car, I get a connection error. Strangely, if I force the fuel pump to work using +B (joining Red wire with green wire) , the engine will start.
Customer: replied 1 year ago.
I mean +B and FP joined will start the car but pump will run at full speed. There is no pulse width modulation coming down the FPC line. Does that mean the ECU is not happy? I tried to connect to the ECU using an ODB1-> odb2 wireless reader but so far no luck.
Expert:  indy-tech replied 1 year ago.

Sounds like a bad ECU.

You need to try another .