Fuel pumps...

U

unity

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I have a theory on my cut out problem. Anyway, I noticed the 96 has a two speed pump? Do all Marks?
 
So there is really no "two speed" pump. How does the ECU control the "high speed pump"?

I am now very sure I am only getting low speed.
 
I know, but the ECU commands the VRCM. Its the VRCM I suspect is bad, or a wire considering this car is ancient.
 
The VCRM and VLCM's in Markviii's uses whats known as PWM. Pulse width modulation. This is the normal power system for the fuel pump. When the ecu grounds the fuel pump controller, it sends power thru the pwm circuitry. This reduces pump speed/output, without damaging the pump. This was designed to limit recirculation of the fuel, thereby limiting heating and outgassing of hydrocarbons.

During heavy loads or wot, the ecu will command the VCRM or VLCM via the databus (scp protocols), to ground the fuel pump relay. This is the relay located inside the power distribution box. This will now give you full pump power.
 
Ok. And I did swap that relay with another too. I really think its not getting full power. I am going to again get pressure readings.
 
What would be the danger of wiring it to always run in "high speed"? I assume pump life and heat?
 
Psychostang said:
The VCRM and VLCM's in Markviii's uses whats known as PWM. Pulse width modulation. This is the normal power system for the fuel pump. When the ecu grounds the fuel pump controller, it sends power thru the pwm circuitry. This reduces pump speed/output, without damaging the pump. This was designed to limit recirculation of the fuel, thereby limiting heating and outgassing of hydrocarbons.

During heavy loads or wot, the ecu will command the VCRM or VLCM via the databus (scp protocols), to ground the fuel pump relay. This is the relay located inside the power distribution box. This will now give you full pump power.
Click to expand...

Yeah, what this dude said :)
 
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