I have a 90 Q45 which is making the dreaded "humming sound" from behind the rear seat. My understanding is that the fuel pump needs replacement and I have found a lot of good info here to help me with that.
My question is whether the controller needs replacement also. I have seen the posts regarding voltage output,etc but am not electrically inclined in this area. The car runs very smoothly. Would that indicate that the controller is in good working order? I would rather not spend the bucks to replace the controller if I can help it.

Thanks in advance for your help
Skruser

Welcome to NICO!

Heath

That occur after pump replacement [even years after pump replacement].

Why dealers like to replace controllers with fuel pumps, as controllers can be partially bad or go totally bad subsequently.

The 3 step voltage can be hard to accurately measure and a missing of the middle step or 3rd step can occur............also the lowest voltage can go away momentarily and the engine brought back by pushing on accelerator which brings the 2nd step on line.

Wierd things from intermittent controller pump voltages.......may lie in waiting when the NEW pump becomes used after a year or two.

Of course a new filter is required.

Discover the power of the button!

See rides section for pump photos

I suspect the fpcu was designed to fail to get owners [attention] to replace noisey pumps caused by water injestion.
They used the same design for 6 years, then in 97 they added a big safety resistor around the unit [pump to ground] to share some of the current load.

My first [fpcu] unit was not changed until 14 years old when it finally became intermittent............after being used on 3 fuel pumps....[none failed just got too noisey for me].

260,000 mile life is good enough for me.

Chicken or egg..............but when a load draws more than design current you cannot fault the controller for over heating and eventually failing.

Years ago I mentioned getting a 15 amp 3 position switch and wiring it in the line between the pump and controller: On#1 to controller, center open, On#2 to ground.........perfect fail safe, perfect car theft immoblizer..............mount inside rear shelf storage tray...........could be a keyed switch for more protection.

The problem with the resistor safety bypass is heat generation, never tried to duplicate but 6-8 volts x 4 amps= ~~ 30 watts.

Someone could experiment and determine what value works the pump at minimum usable speed with no [open circuit] controller.

http://www.stealth316.com/2-fuelpumpguide.htm
http://www.lindertech.com/fuelpump.htm

"Most OEM's suggest removal of the entire fuel tank and a total flush of the tank unit prior to pump replacement.
Repair facilities have shown some reluctance to do this service as suggested! This will compound the damage done to returnless systems as multiple pump replacements are common on these vehicles"...........because pumps only have 12 month warranty and most last longer than this without the tank removal service!

Other manufacturers COPY Nissan FPCU:

http://www.babcox.com/editorial/us/us50146.htm

Can't wait till the new returnless systems start throwing a fit!

It will cost $1000 every 70,000 miles.

a) Fuel pump gets old or clogged or both.
b) Fuel pump draws more current & hums.
c) Fuel pump control unit takes a beating.

In my case, after a long period of humming, the ground connection on my fuel pump control unit printed circuit board melted to an open circuit. Fuel pump stops instantly. Car glides a bit farther.

The solution - replace the humming fuel pump AND re-solder the fuel pump control unit wiring AND add an extra copper wire (to beef up the weak trace) as shown in the photo below.

Again, the detail is in prior posts so, I stop here.

Tangalora

Attachment: nico_q45_fuelpump_controller_solder_wire.jpg (20808 bytes, downloaded 2993 times)

a) FPCU printed circuit board melted.
b) Fuel pump stops instantly.
c) Car glides a bit farther.

Dennis' suggestion to ALWAYS keep an aligator-clip wire in your trunk comes into play while your're stuck on the roadside shoulder.

From the Q45 trunk compartment, simply:
a) Remove the forward-facing bulkhead, AND ...
b) disconnect the fuel pump control unit connector ... AND
c) Jump the ground wire (see photo).

This totally bypasses the fuel pump control unit, which will handily get you home (albeit with a fuel pump whirring away at top speed).

Again, this is all stated in prior posts so I won't delve further into rehashing messy details.

Tangalora

Attachment: nico_fuel_pump_emergency_jumper.jpg (18464 bytes, downloaded 2974 times)

Normal, Center Off [car immobilizer], and emergency high pump speed Position [pump just grounded] for FPCU failure or just to ocassionally test FPCU.

Even nastier from a car thief prospective would be a 1-2-3 minute delay cutoff module POSITION. Which could active a sound module " CALL THE POLICE THIS VEHICLE IS BEING STOLEN TO GET A REWARD"

You can buy 3 way rotary switches with a removable key.

You need to remove the rear deck cover (which means you need to remove the rear seat) to unscrew the FPCU from the body. You remove it from the trunk, but you have to unscrew it from the rear deck.

Heath