How to tell if fuel pump is going bad?
 

A few months ago I ran over a dead deer going about 70 mph, but due to my LTB and SFCs, nothing was visibly damaged. Soon afterwards I noticed that when I got below ¼ tank of gas my car would sputter pretty badly. The fuel tank isn’t visibly damaged, but I get the feeling that the fuel pump might be dislodged or damaged. No codes are being thrown. Is there a way to tell if the pump is damaged without taking it out? How would I know it’s damaged when I remove it? Could something else have been damaged when I hit the deer that I’m not thinking about?

Since there is no problem when the tank has more fuel, the pump is probably okay. Could be like you said, the pump is dislodged due to the impact, thus its pickup tube does not reach the bottom on the tank. Or the tank or frame may be distorted (tilted). As far as testing the pump, you need to measure flow rate and pressure. Not easy.

do you hear a whine? louder than normal of course. like ^, i doubt its bad if it works ok with high fuel levels, but you never know. the pickup tube theory sounds a lot better

a whine like you have a supercharger

nick, did you consider that one of your fuel lines running under the car may be damaged? If so, perhaps under 1/4 tank the pump is not providing as much pressure or something :gotme:

i think you're just saying this so you can get out of autocrossing again ;)

well more likley that ur pump could be a pinch in ur line... whici wille ventlually over exasperate the pump and lead it to an early death... get it on a lift if u can..

Had the same problem and ended up with a bad pump about 6months later.

I would think it is a pinch or bend in the fuel lines. Since the fuel lines run under your car along side the frame rails. Look there first.

I have a 1997 Maxima & am having major problems starting the car. I have changed the STARTER,IGNITION SWITCH, COMPUTER,FUEL PUMP, FUEL FILTER,TIMING CHAIN, CRANKSHAFT & CAMSHAFT positioning sensors, cold start sensor & spark plugs, fuel pressure thingy. it runs great when it is on. I have notice the idling to be really low now. Anyhelp would be great. I took it to a NISSAN DEALER & they had no clue.

The car will crank over really good but seams as though it is out of gas for about 8 cranks. NISSAN said they checked the fuel pressure & it was good.

Hook up the fuel pressure gauge to the fuel line and check if the pressure is within specs.

I'm not sure where you can get one though... maybe you can borrow it at AutoZone :gotme:

Edit: I believe that's the only way to tell if it's going bad.

A/t Interlock relay? It could be sticky
Hard start is usually fuel pump

low fuel = rough running in a 98 Max
 

Was this ever resolved? What fixed it?

I have a 98 Max (125K) that didn't hit a deer but also runs better with a full tank of gas than with a low tank.

When it gets below a 1/2 tank it starts a little harder and when it gets below 1/4 tank, not only does it start harder but it also sputters and/or surges at highway speed. When I accelerate a littler harder than normal, with a 1/4 tank, it acts like a dirty fuel filter - but the fuel filter is only 3 months old. (premium or regular gas makes no difference... except in my wallet)

Last fall I swapped the fuel pump in an attempt to fix another problem (which turned out to be a leaking intake) but I put the original pump back in since the brand new O'Reilly pump made so much noise (loud whining). (the tank and fuel pump strainer were clean and I had no problems getting the pump in and out - it was firmly in place when I finished)

My original fuel pump is not whining or making any noise that I can hear. I asked a younger friend to listen, he says he can't hear anything either... the car does run quite good... but only with a full tank of gas.

Any suggestions? And if it is a pump, what brand of pump do you recommend?

Thanks,

dersh.

If the pickup tube is dislodged or broken, or the screen is deteriated or torn, the pump will suck air instead of fuel after the fuel level drops below the damage.

what was the outcome of this. Im having issues with my car as well. sounds similar

umm i put a pump in my maxima when i was having a smilliar problem and that didnt fix the issue

I am bringing this thread back up because I am having the EXACT same issue as the poster a few posts up. My car runs fine with a full to 1/2 tank of gas. But, when it drops to about 1/4 tank, not only does it have a bit harder time starting (although it always starts up after just a few cranks) but it has a REAL hard time with gear shifts and acceleration just after it has downshifted or accelerating from a dead stop. At first I thought it was transmission related, but I'm beginning to think perhaps this is my issue instead, since a) it seems to be OK with more gas in the tank, b) there are signs of undercarriage damage (I bought it used) and c) the acceleration problem is not just right when it has downshifted, it also occurs when taking off from a dead stop.
Can someone please outline exactly how to check the fuel lines, pickup tube and/or screen to determine whether that is the issue? Thanks

Chances are your fuel pump may have come loose from the assembly, or there is a problem with the assembly or pickup. Think about gravity and the movement of fluid in the tank. If you stomp the gas and lose power with a low tank, it's probably because the pump is only getting air for a moment before the fuel move forward again.

Here's what I'd suggest doing. Best to do this with a low tank.

1. Go to your backseat and pull the 2 tabs under the rear seat to remove the cushion. Just 2 tabs on each side, right under the cushion. Pull em forward and pull the seat up. Disconnect the negative terminal from your battery as well.
2. Under the cushion, the fuel pump assembly is dead center. You can't miss it. Use a screw driver or sockets to remove the electrical cover.
3. Unclip the electrical connector to the fuel pump as well as the fuel line. It can be difficult, so be careful not to break the clip.
4. Use a ratchet to remove the bolts and pull the assembly up.
5. Check the assembly for loose parts or that things are all in place.

I had to deal with this with my custom setup, which consists of a suspended pump, held by injection hose, and a long hose for feed that just sits down in the tank. It once came loose from the assembly and would spray fuel at the top of the tank (and somehow I still could drive... for weeks before I narrowed it down). I also suffer from the choking with a low tank, because my fuel feed is towards the front of the tank. I need to get a longer hose and route it to the back so I can get power under torque with a lower tank.

All I can say is that I hope this helps.

Clogged fuel strainers can also cause these kind of issues. Its a $5 part so i would replace it too. Also knock out that fuel filter under the hood. That can actually massively improve performance depending on how dirty/old the one installed is.

My pump whines a bit, but maybe for a few seconds and ONLY after it sits for 30 minutes or so after a run and is restarted.. Cold starts are no problem. No other issues.

Is this anything concerning? It doesn't seem to get any worse. Been doing it for maybe a year or more. Just thought I'd ask.

Check long and short term fuel trims with a scan tool. Looking at the data at idle, on a warmed up engine, ideal would be 0 or close to zero. +/- 10% is considered acceptable. If your number increases with rpms, you can suspect a fuel delivery issue or dirty maf sensor. Check idle, then hold 2k rpms for 30 seconds, then 3500 rpms and note the changes on both ltft and stft .

This strategy applies to all types of cars and is best viewed in generic obd2 modes, which is nice since the scan tools are nice and cheap that can do this.

If your numbers are + and rpm brings them closer to zero, you have a vacuum leak .