Fuel Pump Infiniti Q45 - 1991

[VBasa2727]

Hello everyone,

My Fuel Pump just went out on my 1991 Q45.

About a year ago, 5K miles, my car stalled on the roadwhen something happen to the Fuel Pump Computer.

I unconnected all the connections, and saw that oneof the connections looked burnt, almost melted!

So, I wired that wire, of the fuel pump directly to the ground, giving the fuel pump 12V all the time.

I did this on my 1990 300 ZX when it stalledon the road. (All the connections look good,so I think something happen to the fuel pumpcontrol unit on the 300ZX)

On my Q45, not sure if the Fuel Pump Control unitalso went bad, or just the connector.

Eitherway, the Fuel Pump is gone, and I was thinkingof replacing it with some sort of better Fuel Pump,that can operate at 12v all the time, so as tonot worry about replacing, and or the Fuel PumpComputer ever going out again.

So, my question, is if anyone has had any experienceusing an after market fuel pump, and with out using the Fuel Pump Computer that adjusts the voltage, so as to run the fuel pump at 12v all the time.

Thanks for all your help,Vinay

[maxnix]

Read the previous posts by Q45tech. There is a reason that Nissan set it up as a 3 stage pump.

Some have adapted a Walbro, but most of us (99.9%) use the Nissan designed fuel pump and controller. Sorry you ignored the warning signs and fried your FPCU.

Read Tangalora's excellent posts in this Forum on how to R&R properly.

[Q45tech]

Important to understand that the life of a motor [fuel pump] is directly related to voltage. The oem system only operates at full rpm when accelerating [near WOT] or during a cold crank for 3-10 secpnds.

Most fuel pumps last 160,000 miles if you repalce fuel filter every year and don't buy bad gasoline or E10.

To avoid STARVING the engine at WOT no smaller pump will last you must have a 255 lph [60 gallon per hour] unit.

The dynamic range from idle to high rpm WOT is over 30:1.The engine makes ~ 10 HP at idle without AC in park to overcome friction.

[VBasa2727]

Thanks for the info guys,

So, seems like the best option is toreplace the FPCU and Fuel pump!

So here are my next questions.

By the way, my mechanic experience has beenon race cars, and minor road cars. Race cars are a lot more simple, so I don't do much workon my road cars myself.

1 - Instead of using the stock pump, would it be possibleto use an external pump, like a race pump, and keepit running at 12v all the time?

(Personally, I'd like to do away with the FPCU, keep it simple,and with an external pump, I figured I can change it easier,and are maybe even have 2 in parrellel hooked up, and useone, and if one goes out, flip a switch for the ther one.)

2 - Are the Q45, and 1990-96 300ZX on a returnless fuelsystem, so is that why nissan use the FPCU toregulate the fuel presure?

3 - When I bypassed the FPCU on the Q45, I rememberseeing one of the contacts in the connector sort of burnt, can't remember if it's on the FPCU side,or the wire. Do I need to replace the wire too?

Thanks again,Vinay

[Q45tech]

Every electric fuel pump is driven by an electric motor which like all electric motors slow down with wear. As electric motors slow down the amount of current draw increases. As the current exceeds the contacts ampere rating the contacts overheat and burn creating intermitents.

Transistor are rated in amperes and as you increase they over heat and fail.

The problems is always owners not paying attention in Physics or electrical engineering or even trade school classes in automotive technology before purchasing a vehicle.

Things fail and need replacing at intervals.

Failure to replace a slow running fuel pump will always destroy the fuel pump speed control circuitry.

Modern vehicles are all about electronics and failure to keep up in education will leave you sitting on the road.

Electric/battery vehicles are even more complicated and will require more technology education.

I am scared for people who think 20 year old technology is cutting edge!Every state and county has almost free to cheap votech schools with great automotive technology courses day, night and some weekends.

Consider how an electric vehicle adjusts its speed with a GIANT FPCU to vary the current and voltage to the driving electric motor. But instead of 12 volts and 10 amperes it must deal with 400 volts and 100 amperes.

Battery banks are divided in half/quarters for charging from 120/240VAC then put in series to drive.

[VBasa2727]

Thanks for the info Q45 Tech,

I just got the new fuel pump, and plan on putting that in,and trying to repair the FPCU like tangalora. Also puttinga switch in the lines as a back up for WHEN the FPCU fails.

NExt question, I don't remember, and I'll find out this weekendwhen I take it apart, do I need to replace the wires also?

I remember one of the metal contacts looked sort of burnt,along with the plastic harness. Not sure if it was on the wireside, or the FPCU side?

Best Regards,Vinay

[Q45tech]

Many cannot make the mental correlation betwen fuel pumps and fan motors [HVAC] as both have variable speed controllers and both motors fail at approximately the same number of running hours [by design].

In many ways the window motors, sunroof motors, seat motors, windshield wiper motors, condenser fan motor and radio antennae motor are all very related in design with the above units.....................except they are used less frequently.

A 12 volt DC motor with brushes is a 12 volt DC motor with brushes.

[VBasa2727]

By the way, when should you change the fuel pump?

My 300ZX TT, the fuel pump went bad (FPCU went bad), at around 60K miles. The Fuel pump is bad, I use it as a city car, so I'm running the pump at 12v with out the FPCU.

My Q, the pump went bad around 160K, and I've driven about another 10K miles with the pump at 12v, bypassing the FPCU.

How do you know to change the Fuel Pump, before damaging the FPCU?

Thanks,Vinay

[Q45tech]

Simple you read the pump rpm [with an oscilloscope] and the pump current [with an ampere meter] at the 3 different speed functions.

Easy to SEE if the pump has 8 equal current spikes and displays a uniform display.

All this like observing fuel injectors can be done in minutes by substituting a loop or sensor in place of the correct fuse.

Hearing the pump whine at any time other than the first 5-10 seconds after a cold crank is a CLEAR WARNING that a replacement is needed.

A new pump spins too fast for humans to hear as it ages and slows down it becomes audible.

Read this story:http://www.asashop.org/autoinc...h.htm

[jjggq45]

Several years ago, we had a mechanic or so we thought, replace a bad fuel pump. Recently, we are having fuel pump issues again. After removing the access to the fuel tank, we noticed that the mechanic only installed an electric fuel pump. He never pulle the old one out. It ran fine for several years. Now we also looked at the control unit. One point was burnt out and the circuit card was torched in that area. We visited a salvage yard and found a control unit and fuel pump from a q45t. They were in good shape when we bought them. After installing the controller and pump, a transister burned out. We replaced it with a resister from the old controller. It doesn't seem to be controlling the speed of the pump as it should. Did I mention that the past mechanic spliced several wires. So we are unsure of the order and color of wires going into the controller plug. Does anybody have pictures they could send me that shows what wires belong where? Thank you,

[Q45tech]

Download the pdf file FSM for a 1994 Q45 the circuitry for fuel is identical.

[maxnix]

And for those who won't spend the time reading Tanglora's exemplary posts, always use a new O ring and be careful to not confuse it with the old one. Torque the screws progressively in a star pattern and do not over torque!

[Infinitiguy19]

No offence but you can't confuse the old VS new one. Because the old one is ALWAYS bigger than the new one, Thats because the fuel causes the rubber one to expand.

[maxnix]

No offence but you can't confuse the old VS new one. Because the old one is ALWAYS bigger than the new one, Thats because the fuel causes the rubber one to expand.

What's a VS?

Many have found the O rings to be visually identical, if the pump is replaced in time before it fails completely.

[Infinitiguy19]

VS=Verses

I can tell you from my 1991 Q45 that was hacked to hell by a bad mechaninc at least the fuel tank and pump was. I wish I could remmber his name, But I have never seen one leak at all in 160.XXX miles on a 1991 Q45.

You will notice a differnce because like I said before the gasket expands when it comes into contact with fuel.

[Q451990]

You will notice a differnce because like I said before the gasket expands when it comes into contact with fuel.

This has not been my experience. Perhaps the mechanic who last replaced yours sourced a different gasket from his parts bin?

Heath

[Infinitiguy19]

N/A

[Q45tech]

Remember the owner WHO CHOSES a mechanic is just as guilty as the mechanic, both deserve to be stocked on the town square for 24 hours with tomatoes and wet and dirty pants.The mechanic would changes lines of work and the owners would change also.

98% of car owners are clueless! Not their fault just too busy on other things. they just cannot be bothered to understand the 2nd most expensive thing in their lives.

But even more scarey: "Only 46.5% of the people located where the heart should be located and a whopping 68.6% gave the wrong answer when it came to where the lungs were. "

[valkyie]

Q45tech Quick question I have. I think you answered it for me in the past but I cannot remember your answer word for word.

I have a 300zx NA 2+2 and I have had this problem for a long time. My car shuts off like no fuel. It will crank but will not start up only until a few hours later. I cant remember if you said I might have either a bad fuel pump controller or a bad fuel pump. Either way I have a new fuel pump and a used fuel pump controller just in case.

Can you please explain what might be causing my car to just shut off like it does again for me. Thanks

[in94q45]

My fuel pump has that "humming" sound, not overly loud but you can hear it. I've been told this is somewhat normal for Asian cars/fuel pumps. Should my fuel pump be making any sound at all while I'm driving. Please clarify.

[Q451990]

If you can hear it in the front seat while driving with the radio turned down, then it's too loud. You'll notice it when your fuel level is below 1/2.

Heath