Electric fuel pumps

Sat Jan 04, 2014 9:47 pm

Non-cub machinery for certain. I suspect that I have a failing fuel pump, my first ever for an electric. Posted at a enthusiast website for that specific vehicle and got no help.
Parked at my home for couple of days, trip to make late afternoon. Manual transmission. Cranked the engine and it ran for about 2 seconds and quit. No unusual noises at all. The starter would spin the engine it would not even pretend to start. Drove another vehicle to my destination. Next day sprayed carb cleaner into the intake, pushed the accelerator pedal to the floor and cranked it. Hesitant but it started and then ran well. Shut it off and cranked twice more- started normally. Service Engine light not on when running, so probably no code set. Web search shows that this vehicle does experience fuel pump failures and that finding a long-lasting replacement is not easy-- including OEM pumps.
Strangely, sometimes when I parked this vehicle, got out with engine off and key in hand, the fuel pump would be running for an undetermined time. Thought that strange as it has a fuel pump relay which I assumed opened when the ignition switch is off. And no need for fuel pressure with the engine stopped.
Questions at the moment are: Should the pump run after the ignition is off? Do pumps sometimes become intermittent? While driving, does the pump run constantly or cycle as the pressure drops? As far as I know the pressure regulator (if there is one) is part of the pump assembly on this one as I do not find it as a separate item.
Have at least 3 vehicles with electric pumps that have lasted over 100K miles and one about 160K and either sold the vehicle or am still driving it.
Tell me all that you wish about electric fuel pumps-- something might help me find an answer. Even though this thing now cranks and runs well, I do not trust it. And am not absolutely certain that it is the fuel pump. The old diaphragm pumps driven off the camshaft usually started leaking gasoline externally and there was no uncertainty about the problem-- or the cure.

Re: Electric fuel pumps

Sat Jan 04, 2014 10:16 pm

You didn't provide any information on the vehicle; like age, make, model, engine, amount of rust and previous paint code.

Can't help much - had to replace an electric fuel pump twice on the front tank of a Ford F250. Hardest part is removing the pickup bed.

Re: Electric fuel pumps

Sat Jan 04, 2014 10:52 pm

You did not say if it was in the tank or where, but unless someone has Rube Goldberged the wiring, a fuel pump should NOT run when the key is turned off. Just think about shutting it off in case of a fire and the pump keeps on feeding fuel to it.

Re: Electric fuel pumps

Sun Jan 05, 2014 6:42 am

My 99 Chevy Z71, has 212000. miles. I am on the 4th, in the tank fuel pump, and it makes the same whining noise. One trick is to whack the underside of the tank with a rubber mallet but is only temporary. I have a nearby mechanic, he unbolts the bed and lifts it with a cherry picker, blocks it and changes it. My Father-in-law, cut out a square in the bed of his 94 Chevy, and pulled it, replaced a broken hose and put it back together. Such a pain!

Re: Electric fuel pumps

Sun Jan 05, 2014 7:51 am

Assuming later model vehicle with fuel injection. Most have electric pump in tank. When you first turn key on, if you don't go all the way to start, you will hear pump for a few seconds, building up pressure. At that point, many cut off, I assume waiting for pressure to drop. However, most systems have a return to the tank, so one would think under running conditions, they would run almost constantly. I believe many can show intermittent problems prior to complete failure. The one in my Suburban failed all at once, just wouldn't start. One test is to relieve rail pressure, there is usually a schrader type valve on or near the rail, then turn key to on to listen for pump to rebuild rail pressure. Good luck, if Flex fuel, pump will be expensive (stainless). In all cases it is a PITA to replace.

Re: Electric fuel pumps

Sun Jan 05, 2014 8:18 am

We need more info, as systems do vary a good bit. I've noticed that on some vehicles, the pump will continue for a bit after the engine is shut down, those are usually controlled by an oil pressure switch. Most modern systems control the pump by the computer sensing engine rotation through it's various sensors. Pretty much any vehicle, now days, will have a fuel pump relay, which could give either, or both of the symptoms you mention.
When the pump died on my Buick Regal, it acted like you describe, it would fail to start today but run like a champ tomorrow, it finally left me stranded at my brother's house. Fortunately, it was a very easy pump to access, I changed it in his driveway, through an access panel in the trunk, and drove the car home. The pump failure on my wife's S-10 was different, it would run but was unable to produce enough pressure to run any more than low speed. There was a lot more work involved changing that one. The S-10 failure is most common but not exclusive.

Re: Electric fuel pumps

Sun Jan 05, 2014 3:20 pm

Was deliberately vague as I wanted as much general information as possible. The car is a 2003 Nissan Sentra. It has no port for reading the pressure as best I can determine. Some vehicles do have such a port. My thought is that a pump might supply enough static pressure to appear satisfactory but not be able to develop that required pressure while delivering fuel to a running engine. But starting depends on static pressure only.
First will replace the pump relay. Fellow who really knows Hondas says they have more relay failures than pump failures.
This pump is accessible by removing the rear seat cushion and removing a plate under that cushion. Spilling gasoline in the car would be my worry. Phew!
Anyone ever used a Herko Redline fuel pump? Some say that there are few makers of pumps and most brands simply buy from one of those and then put their own name on the pump and box.

Re: Electric fuel pumps

Mon Jan 06, 2014 10:20 am

I'm not familiar with your Nissan so I can't help you much there. I think most Japanese models have the access cover in the floor, you're fortunate in that respect, just be careful. I don't know anything about a Herko pump, but I suspect your statement regarding few makers would be correct.

Re: Electric fuel pumps

Mon Jan 06, 2014 11:49 am

My added info…not much more than what everyone has said….

With the fuel pump running with ignition switch off is a good sign the fuel pump relay is having issues. The only vehicle(s) that did that (I know of) was 80’s-earily 2000 GM (FI) cars/trucks. They had a failsafe back up if the fuel pump relay failed the engine oil pressure switch was wired in to complete the fuel pump circuit to run the fuel pump. If you turned off an engine and the oil pressure didn’t return to 7-10 psi fast the fuel pump would run until it did. Maybe Nissan has that also…don’t know.

Sometimes a code will be stored, even with no SES light on; to help diagnosis.

If you remove the pump from the car, it’s not that hard…just do it in a well ventilated area.

If you want a Herko pump, make sure it’s for your car, talk to the Honda person and ask what they think. Look in the internet and find out if it’s ok for your car.

You have to have pressure and flow to the specs of your car. Proper diagnosis is important, sometimes you can throw an item (part) at it and hopefully it will work. I know the equipment /education for diagnosis unfortunately comes at a high cost now days, but I know you can do it....just be safe....

Some preventive maintenance on an electric fuel: if you have a outside the fuel tank fuel filter; change it per factory recommendations and try to keep the fuel level in your fuel tank above the ¼ level. The fuel in the tank helps keep the pump cool.

Re: Electric fuel pumps

Mon Jan 06, 2014 4:27 pm

Jack, your idea and mine about the relay are the same. To that end, I replaced the relay today with a genuine Nissan part. This car has a one-line system with no filter other than the one associated with the pump. Apparently Nissan used a "sock" on the bottom of the pump as the filter-- but I have not verified that by looking. The new one has the filter in the housing-- if it has one, and the supplier assures me that it does. Makes good sense to filter the fuel before the pump gets it-- but cavitation can be a problem with restricted pump intakes.
As far as I know this car has no provision for hooking up a pressure gauge for testing. The line from the tank is steel to the firewall where it transitions to non-metallic composite that is not easily cut and spliced.
I think that the new pump will not be installed until I have used the car a bit to see if the problem recurs. The independent garage owner, a wonderful fellow about the age of my children, tells me that sometimes new pumps that he installs fail shortly thereafter. He buys mostly aftermarket parts for his shop. Mostly from O'Reilly's. He is not near any new car dealerships.
Thanks for posting. Any other ideas/suggestions are welcomed.

Re: Electric fuel pumps

Mon Jan 06, 2014 6:51 pm

Bus Driver,

I think your system works like the Ford system. I’ll try to explain from memory from my GM and some Ford training I had when I worked on them.

As for as I know all one fuel line systems are pulse width modulated system. In general the system uses a pressure sensor that monitors fuel rail pressure and sends a signal to the ECM (computer) telling the fuel rail pressure.

On Fords the ECM monitors fuel rail pressure by the fuel rail pressure sensor and the ECM determines the fuel rail pressure by looking at engine load and rpms. When the ECM determines the correct amount of pressure it sends a duty-cycle signals to the fuel pump module and the module duty-cycles the pump to control rail pressure. The General Motors system is similar to Ford’s except that it does not have a fuel pressure sensor on the fuel rail. The ECM tells the fuel pump module what fuel rail pressure it wants. The ECM then controls the fuel pump and the pressure in the fuel rail.

If you can get a Scanner tool that monitors your vehicle ECM, it will show you what your system is doing, then you can compare that to the factory specs.

Hope this helps...

Re: Electric fuel pumps

Mon Jan 06, 2014 9:36 pm

The Nissan relay has 4 terminals and a tiny diagram on the injection-molded body. It is clear that the relay has two terminals supplying power and the other two are the switched terminals. The pump has 5 terminals and I can only guess about them. One is probably ground. one or two are for the fuel level reading and two or three are for the pump operation-- some combination of those to total 5. The pump assembly has no external metallic parts.
Seems that I read somewhere that a faulty ground for the tank could disable the pump on some GM. And that ground is from the tank to the frame. Not a conductor in the harness or connector.

Re: Electric fuel pumps

Mon Jan 06, 2014 10:03 pm

Most of the time an electric pump will act kinda like a starter, you can bump the tank and make them take off but they do not last long after stopping the first time. Like beating a starter with a hammer to get a few more starts out of it.

Re: Electric fuel pumps

Tue Jan 07, 2014 12:00 am

VW pickup I owned for 23 years, if you turned key and did not hear pump, may as well get out the tools. Since mine was bought new with salvage title, no warranty. My mechanic modified the pump relay to mimic factory fix. Later line between pump and accumulator sprung a leak and was spraying gasoline on exhaust pipe. Patched with copper line and two clamps. They could not hold pressure, blew apart. Had to buy new hose from VW, as they were the only source. In '06-'07 drove a Chevy van with pump problems. Would stop running while riding down the road. After a few stops I learned that if I turned the key all the way to off it would restart, but not if you just went from run to start. Got pretty good at it. You could hear the pump standing outside and truck running. Much noisier than my S-10.

Re: Electric fuel pumps

Tue Jan 07, 2014 5:34 am

Bus Driver,
The ground for the fuel pump completes its path to the fuel pump module. This is a video I found in the internet I thought was good. http://www.youtube.com/watch?v=znEeiLobzxg