RB30 Patrol FPCU(Fuel Pump Control Unit) modifed replacement

Hey Guys,

This is how I "replaced" the malfunctioning FPCU(Fuel Pump Control Unit) in my RB30 Patrol.

Prior to this, I've had it hard wired, bypassing the FPCU.

I opted NOT to replace the FPCU using a secondhand unit from a wrecker. The reason is that for the asking price of $50 for a used little electronic unit(see pictures) is NOT worth the trouble, 'cos it will most likely fail again.

FPCU performs an important role in terms of safety.
When ignition is turned on FPCU immediately switches on the power to the petrol pump, allowing the pump to prime for few seconds.
When cranking starts FPCU receives a "signal" from the oil pressure switch and switches the fuel pump power to be switched on using alternator positive wire(white with red trace), rather than battery wire, which is "piggy backed" via the oil pressure switch signal.
The purpose is to turn the fuel pump off in case of an engine stall/engine stop while the ignition is still on.
This is a very important safety feature in an event of an accident, where the engine stops but the ignition stays on. If the petrol pump keeps running in such situations, running fuel in the fuel line towards the engine can cause fire & explosion, hence the importance of the role that is played by the FPCU by cutting the power to petrol pump when engine suddenly stops or stalls.

I have opted to below method of using a PEEL gas safety switch(tachometric relay) to perform the same function as RB30 Patrol stock FPCU, but in a far better, more reliable(and cheaper) way. PEEL safety relay can handle up to 12amp current, so it's more than enough for the fuel pump. Instead of "piggy backed" via the oil pressure, it's now "piggy backed" via ignition pulse.

The only thing this PEEL safety relay switch doesn't provide comparing to the original FPCU is that the "automatic priming function", which in FPCU runs for few seconds to prime the carby fuel bowl with petrol. Now, that function is performed via a manual push button, but it may not be necessary though. Cranking two or three rounds is enough to fill up the carby fuel bowl by activating the PEEL safety switch.

One added advantage of my approach is that since my vehicle is dual fuel, there is NO need for the petrol fuel pump to run when the engine's running on LPG. Of course, full time running fuel pump may help with the quick switching to petrol from LPG bit smoother, while driving the vehicle. However, I've discovered there's still enough fuel between the fuel pump and fuel cut off solenoid(near the carby), so when switched from LPG to petrol while driving, the vehicle doesn't stall and engine switches from LPG to petrol fairly quickly.
In other words, the petrol fuel pump in the petrol tank doesn't need to pump fuel all the time(when running on LPG) all the way from tank to the fuel cut off solenoid/carby at the front in order to switch to petrol from LPG smoothly. There's no delay that causes any issues. There's still enough petrol in the fuel line between petrol pump & petrol cut off solenoid.

It's running good from the tests that I've done so far. PEEL safety relay is a pretty good reliable unit. It's originally meant as an LPG Safety Switch, so using it as a Petrol safety switch also makes sense.

Quote:

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Originally Posted by dom14

The only thing this PEEL safety relay switch doesn't provide comparing to the original FPCU is that the "automatic priming function", which in FPCU runs for few seconds to prime the carby fuel bowl with petrol. Now, that function is performed via a manual push button, but it may not be necessary though. Cranking two or three rounds is enough to fill up the carby fuel bowl by activating the PEEL safety switch.

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I think I may be wrong about FPCU running for few seconds to prime the carby when the ignition is turned on petrol.
I think, when ignition is turned on, FPCU simply forwards the battery +12v to the fuel pump(dark green/red trace wire). When the engine starts cranking or running FPCU switches to be "piggy backed" from oil pressure when it detects the +12V(approx) from white/red trace wire(alternator wire). When the voltage drops(from +12v approx from +1.5v approx on alternator wire) & oil pressure switch closes(vehicle is not running), FPCU cuts the power to the fuel pump wire(darkgreen/red trace).

However, it's important to notice that the FPCU does NOT function as a fail safe mechanism to cut the power to the fuel pump wire(dark green/red trace) when oil pressure drops and oil pressure switch activates(switch closes) on it's own.

In other words do not expect the FPCU to save the engine from getting seized by cutting off the power to fuel pump in case oil pressure drops due to an oil leak or other low oil pressure mishaps.

Both alternator voltage drop(when engine stops or stalls) & oil pressure drop have to happen at the same time for the FPCU to cut the power to the fuel pump. If one or the other( oil pressure drops or alternator voltage drops) happens on it's own will NOT trigger FPCU to cut off the power to the fuel pump.