q45 fuel pump controller

[skruser]

Good MorningI am new to this forum and have been looking through the posts, great information!

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 helpSkruser

[Q451990]

Typically, you don't need to replace the controller unless you wait too long on the fuel pump. Since everything is running fine - I'd go ahead and replace the pump and leave it at that. If you want, pull the controller while you have the back seat and rear parcel shelf out and check for melted solder joints, connector melting, etc.

Welcome to NICO!

Heath

[Q45tech]

Be alert for strange non immediate starting or sudden power/rpm drops, sluggishness on partial acceleration..........vague symptoms of low fuel pressure.

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.

[maxnix]

And if you haven't read all of the relevant posts yet, do plan on steam cleaning the tank and blow out/replace the fuel lines for extra pump life.

Of course a new filter is required.

[texasoil]

I took apart a 'noisy' but working fuel pump (135K) to see what was causing the noise. Found a small amount of 'rust' or corrosion on the tip ends of the spyder holding the rollers. Just enough corrosion on the tips to rub the cage at the close spot. No other wear of anykind anywhere. It would have gone at least another 200K miles in my opinion. I think 90% of 'fuel pump' failures/problems are due to faulty design and assembly of the pump controller board. It has the current running through a very small section of circuit board foil right at the pin-out. Easy to resolder and install a 'jumper' to another hefty foil section 1/2" away.

[texasoil]

DO NOT put water in the fuel tank or clean it out UNLESS there is a bunch of crud.

See rides section for pump photos

[Q45tech]

Measure the current as the pump ages. I goes up like any used electric motor..........look at the current waveform, you'll see that each commutator varies in shape and current.........changing pump's normalized speed.

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-fuelpumpgui ... elpump.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.

[tangalora]

The humming problem, as I understand it from Dennis (and what happened to me) is:

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

[tangalora]

Oh yeah, after the part where the:

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 ... ANDc) 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

[Q45tech]

Again I point out how EASY it would be to interupt the ground wire from pump to fpcu with a 3 way 15 amp toggle switch [mounted in the rear package tray].

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.

[thsmd4u]

This is my first post. Great information. Is it easier to access the fpcu from the trunk or throught the back seat?

[Jesda]

Aww, and I thought Tangalora came back.

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.

[RandBdude]

i just replaced my fuel pump and i'm not getting any fuel flow through the fuel line and it not pumping out of the tank. Also my fuel pump not turning on could it be my fuel relay is bad i changed it and my fuel pump came on but now i'm not getting anything and my right possitive batt hook has broken from the positive pole does that have antthing to do with it.

[qship96]

Whats a "battery hook"?

[RandBdude]

ok i'm talking about the batt terminal cable with the red fuse like box hooked to it the part the goes around the terminal has broken i was wondering does that stop the fuel pump from getting all it's power to work cause i have it rigg up

[Q451990]

I would certainly fix that first. Having one that's loose - not even visibly loose - has kept my old car from starting. It'll make contact enough to power accesories, but not handle the load of the starter.

Heath