Help! Replaced fuel pump and filters and can't keep it running.

[FastWoman]

Chad, we were taking a long drive yesterday in my Z, and the engine just upped and quit on us, sputtering for about 10-15 sec and then leaving us to coast to the side of the road. See my "humble pie" thread in the "help" section. I found my fuel pump was running at a slightly higher pitch, slightly louder, with a faint "growl," rather than its usual, quet, rubbery rumble. This growl sound is apparently a no-load condition for the pump. The interesting thing is that the pump WAS running. I don't know whether it was cavitating or pumping air or what. Anyway, we might have the same problem.

FAIW, if you're pulling a vacuum of 16, your motor is running strongly enough not to die. It sounds like you've got something else going on -- just like you're suspecting, an interruption of fuel suuply to the engine.

As long as your fuel pump relay is pulled in, it should be supplying steady current to the pump. I've never known current from a relay to go weak while the relay remains actuated. Sometimes relay contacts can become burnt and not make a good contact in the first place, but what you have when the relay makes is what you should have until it breaks.

The drop in voltage when the fuel pump is making noises is particularly interesting. It could be that the pump is drawing more current, perhaps because it is getting jammed up with some crud or something?

Your problem might also relate to a rather overstressed electrical connection for the fuel pump wire, as a part of those two very large electrical connectors just inside the passenger firewall. My connection had started arcing at one time, and eventually it melted that part of the connector. I cleaned up the connector a couple of times, only to have it fail again. My solution was ultimately to clip that wire out of the connector and to use a bullet connector to make the connection. That connection hasn't failed me since then.

So it would be interesting to know whether your engine refuses to run even when you can hear the fuel pump running. You might want to do what I did. It was a simple thing. Just wire a momentary switch to supply +12 to the fuel pump relay's coil. You can use the switch to prime your fuel rail if you lose pressure. You can also use it to run your pump manually, just to confirm it's operational.

[two50below10]

I did a few more checks yesterday.

1) With the fuel pressure gauge hooked up I plugged the other end of the "T" that would go to the fuel rail and momentarily ran the pump. The pump was able to push the pressure up to about 72PSI. So I know the pump is good and strong.

2) I then connected the line back to the fuel rail and disconnected the return line back at the tank. I ran the pump to make sure I had a clear return all the way back to the tank. That checks good also.

3) After putting it all back together I was able to get the car started and kept it running yesterday afternoon while I had the fuel pressure gauge hooked up and the vacuum gauge hooked up. With the engine running the fuel pressure reads 30 and the vacuum reads about 16 and will go up to about 20 when revving the engine.

Confident that keeping it running for 20-30 minutes at idle as well as revs up to 4000, I figured maybe my ghost problem had gone away. I pulled it out of the garage and into the street where it promptly died. Had to push it back into the garage (again!)

4) Later that evening I checked compression on all six cylinders. They were all 105 to 115. So I believe that checks ok. I couldn't find a number in the book other than that they should all be within 80% of one another.

I had a friend who used to work on cars professionally come over to maybe help me diagnose and we couldn't get the damn thing to start. He pulled plugs and they were covered in fuel so I think fuel supply is not the problem. We checked spark while a plug was out and it is getting spark just fine also.

I will definitely hot wire the fuel pump as suggested though to make sure that an interruption in fuel supply isn't the problem, because when the car struggles and quits it does sound as if the pump is not behaving. That could be a result of volts dropping off to the pump as the engine looses RPM and is about to quit though.

I am leaning now towards the AFM. Do any of you have thoughts about whether that could lead to some of these shenanigans (runs great in the garage once and quits when in the street, then can't get it started later in the day)?

Thanks again guys!

Chad

[FastWoman]

I did a few more checks yesterday.

1) I am leaning now towards the AFM. Do any of you have thoughts about whether that could lead to some of these shenanigans (runs great in the garage once and quits when in the street, then can't get it started later in the day)?

Yeah, vibrations and bad connections. Check that firewall connection.

[Willoughby Z]

I have had similar problems in the past and my case, I found some tweaks (and contact cleaning) to the throttle switch were necessary and it helped.

There were still some intermittent fuel pump issues, or so I thought. After verifying good fuel pressure and delivery, I opened up the AFM and found a problem . The spring that catches the counterweight (soft-stop) was missing and the post that holds the spring was missing (broken off). There was evidence of an epoxy, like J-B weld, as if a PO had attempted to fix the post that holds the spring. Obviously it broken off again, as I recently found the piece in film canister with other scrounge hardware. But no spring. In the meantime I had fabricated a solution (drilled/tapped) a small screw with a silicone rubber bush as a sleeve over the screw, to prevent overtravel of the counterweight. The overtravel allowed the attached "pointer" to open the contacts for the fuel pump switch. Recently, the car experienced a condition wher it would start, run for a few seconds, start to stumble, then stall. Eventually I reopened the cover to the AFM and found that the screw/post had loosened, allowing the bumper to shift, again, causing the counterweight pointer/trigger to just barely tickle the fuel pump contact switch. I could hear abnormal sounds from the fuel pump during the stumble/dying stage right before it died. I believe if I had been reading voltage from the FI relay or pump, I might have seen variations, as the fuel pump contacts were right on the "hairy" edge. Not quite closed, not quite open. Repositioned the post, tightened it and no more problem.

I'm not saying that you have the same problem, you've had some great support and advice and you should follow it. Some times, the oddest thing can throw you after you have checked and verified the basics.

[two50below10]

Thank you to all. I agree that I have been given some great advice so far and I have tried to follow through on as much of it as I am able.

Here is another update and a few more questions for the forum. I did go through and check all electrical connections at the fire wall. Everything looks good as far as I can tell. I then decided to hook up the fuel pressure gauge once again since I was concerned about the noise in the fuel pump sounding like occasional cavitating of the pump. This time when starting the car it ran fine for at least 20 minutes. I pushed the hood toward closed and took it into the street. Like usual it started to struggle, so I jumped out to observe the fuel pressure gauge and for the first time I was able to notice that the fuel pressure did start to drop off as the car began to quit. I had never witnessed this in my previous trouble-shooting.

After getting it back into the garage I direct wired the fuel pump to the battery once again and for the first time the pump created very little if any fuel pressure. I am now strongly leaning toward something blocking the pickup in the fuel tank. I think that I am going to drop the tank again and start over with a fuel delivery problem. Thoughts?

The last time I had the tank out I discovered that there are no access panels that allow access to the inside of the tank. The only openings are where the quantity gauge float goes in and where the filler hose connects. Additionally there is a baffle in the tank that keeps from view the fuel line pickup and fuel return.

So, how would I go about gaining full access to the inside of the tank? I know some of you have talked about coating the inside of fuel tanks to prevent corrosion, but did you have access panels that made access to the inside easy?

Also, I have noticed that the fuel tank will become pressurized after the car has been running for awhile. Is this normal or should this tank be breathing and equalizing pressure with outside the tank?

Thanks again for any input you guys might have.

Chad

[FastWoman]

Chad, as I said previously, I think we might have the same problem. I observed the same thing yesterday with my fuel pump, except in my driveway. It wouldn't be the first time a new/fresh part has failed prematurely.

Here's how you can check for a blockage (from crud/rust), vs. just a weak pump: Simply put a hose on the outlet of your fuel filter, run your pump, and pour whatever comes out the other end of the hose into a gas can. Whatever flows out the hose is going through your filter screen and your fuel filter. If that's enough fuel to run your engine (and you can be the judge), then a blockage is not your weak link.

FAIW, I got a reasonably healthy stream out of my pump when I did this. While running the fuel, I also squeezed my intake hoses, and they did not "want" to collapse (as though there were any sort of vacuum on them). I compared how they felt with pump running and pump not running and felt no difference.

My pump simply faded away in its ability to support the required fuel pressure and volume, pretty much just as you described above. It would test fine in the driveway, but when I took my car out on a drive, I'd end up with a dead engine. Now I've re-created the entire problem with my car sitting in the driveway, the pump hot-wired, and a clear return line delivering fuel back to the filler tube of my tank.

I have a new pump on order and expect to be cruising the Colonial Parkway next week with it. (BTW, you can get a new Nissan part on Ebay for $222 +S&H from Chesapeake Nissan. I believe there's still 1 left.)

In answer to your questions: Yes, your fuel tank will sometimes pressurize a little bit. There's a check valve on the vent system that you might check, per the FSM. The check valve is located in the general vicinity of the fuel pump. It goes between your fuel/air separator and your carbon canister. The access holes you found in your tank are the only ones. You can also drain your fuel and see if any crud comes out the bottom. If your tank is like mine, you won't have any view of the intake screen. The only way to gain access to that part of the tank is to cut it apart, which will be expensive. A radiator shop can do that for you. I was quoted $400 to cut apart my tank, clean it, coat it, and weld it back together, and paint the outside. I decided that was way too expensive and that I should service the tank myself. It turns out my tank was almost spotless anyway. Glad I saved the $400.

Edited May 1, 2011 by FastWoman