Fuel pump problem

[Jerry Parks]

I just installed another fuel pump, after my old one quite sending fuel though the lines. Guess what? I did not cure the problem after installing the pump to the assembly that goes in the tank. The pumpassembly does not pump any fuel up to the metalconnections at the top of the tank. The pump motorthat I installed is pumping strong. I can here it goinggreat guns when I turn on the key. Is one supposedto replace the complete tank assembly when the oldpump motor fails? Is some other part of the tank assembly not working? I dont think its the controller, because the pump motor works continuiously as long as the motorcontinues cranking. Help! BTW: Its a '90 Q45.

[Q45tech]

Did you get the power wires crossed so that the pump is running backwards?

[Jerry Parks]

I put the red wire on + and the black one on -.

[maxnix]

Just for grins, why don't you measure the voltage to confirm the wires are coded correctly.

Is the car still apart so you can inspect the pick-up? If it is not part of the fuel circuit, will it pressurize the tank?

[Jerry Parks]

I removed the pump assembly back out of the tank to besure I had it wired and bolted together properly. It looks OK. The old pump worked weakly and did not pump anyfuel out of the tank either - so I'm thinking I've a problemelsewhere. Any sensors that I need to be aware of? Could Ihave a problem any another part of the pump assembly?

[Jerry Parks]

BTW: I also checked to make sure the tank had a decent fuel level and there appears to be no gunk buildup in thetank.

[DAEDALUS]

Did you actually measure the voltage? It'll tell you 2 things: 1) as Maxnix said, whether the wires are colored correctly (polarity), and 2) whether the pump is getting enough voltage. Should be around 5.5-6V at idle, if I recall correctly. Did you notice any burn marks or melting on the connectors between the pump and the controller? I think worst case, you're looking at a bad controller (~$380), but I'm hoping to eliminate every other (cheaper) possibility before throwing parts at the problem.

[Jerry Parks]

yea, I checked for any burn marks-found none. The reasonI eliminated the controller is because the pump appears to be running strong from the noice I hear from the tank with the rearseat out. If its running at all, I would think I would at least geta trickle of fuel out the top of the tank. Also do I need to connectboth the lines back to the tank, replace all the tank screws andre-install the gas cap to make it work? I did not complete the fullinstallation process before I checked for fuel

[Jerry Parks]

Well, I finally got the fuel pump problem solved. It took a callto my old buddy at the Nissan place. He told me to cut off theintake bag filter on the pump and it would work fine. It does.He says a lot of guys replace fuel pumps, thinking they are bad,when the problem is just the intake bag. The odd thing is I blewair though it to see if it was clogged. Air would go though it, butnot fuel. He says that filer is not a big deal either.

[Q45tech]

The oem pump comes with a new filter attached?

[DAEDALUS]

Yeah, mine did. I just had to attach a short length of fuel hose to it.

[Q451990]

I think he's referring to the plastic strainer "foot" on the bottom of the pick-up hose.

The one that traps the really big stuff like oak leaves, drowned rats, big chunks of rust, etc. I really don't see why that would make a difference in the way the pump works - I've never heard of removing it to fix a problem, but who knows?

[DAEDALUS]

Yeah, that's what I meant, just not being clear. By "it" I meant the pump assembly, not the strainer bag. After 200k+, I didn't see any crud build up on the mesh, but it wasn't as bright-white as the new one.

[Q45tech]

"He says that filer is not a big deal either."

Seems like a big deal to me if it was so restrictive that it failed to allow the pump to pump thru it.

This is what helps keep the pump from grinding itself to death in 1,000 miles! The grit from fuel is what wears out the commutators in the motor that drives the pump.

A clean new sock is critical!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Jerry Parks]

The sock was not stopped up due to crud. If even passed air.The dealer guy told me that the sock is made of some uretanematerial that changes its composition after repeated expose toadditatives in gas. The point that I wanted to make is one shouldnot replace the pump without first replacing the sock or discarding it. Why not check a relatively inexpensive fix first before buying an expensive fuel pump?

[Q451990]

I thought the pump came with a new sock installed... at least that's how mine showed up?

Heath

[Q45tech]

Never seen a sock stop up/change density [but then again our Southern gasoline is more benign]. Sure the white turns to amber from the attacking gasoline just like the shiny aluminum in engine turns amber from oil.All the multi hundred pumps we have changed failed from wear, we have examined many internally and the commutators [rotating contacts] were worn down and pitted from dirt....................so in a sense the sock filter was not sufficient to remove all the dirt you [owners] pour in the tank at fillups!

[tangalora]

There is indeed a noticable difference in the color of the old and new fuel sock (see attached photo).

[Q45tech]

"The sock was not stopped up due to crud. If even passed air." ?????? That means what?

The molecular size of fuel vs Nitrogen/Oxygen is how many Daltons?