Rough running when hot

#31

Gauge is installed. Between fuel filter and rail. I read a consistent 32-34 psi while running.

Al, when you say that the fuel rail is supposed to stay pressurized for hours after the pump is shut off, I believe that I would continue to see a reading on this gauge, in it's current position, correct?

Once I shut the car off, or the pump quits (a few seconds after the key is turned to the "on" position), the gauge will drop to zero.

Is my pump not maintaining the pressure? FPR bad?

#32

Well once the pump turns off, it makes no pressure. The only things that hold this pressure in is the one way check valve right before the pump, FPR and injectors (cold start valve too). Have the injectors ever been maintained? my guess is that they are all crudded up and now they leak

#33

The injectors are all 6 mos back from Witchhunter cleaned and tested. ALL of them are good. I would not expect them. I basically moved a 280zx fuel rail over to my car when I did the injectors so I have gone thru all of the components recently.

I have been operating under the assumption that the pump runs for a moment with the key in the "on" position to "pressurize" the system and that the pump holds this pressure. If this is correct...I would expect the gauge to maintain the 32 reading once it stops pumping.

Please correct me if I am wrong.

#34

83_maxima wrote:snip- I have been operating under the assumption that the pump runs for a moment with the key in the "on" position to "pressurize" the system and that the pump holds this pressure. If this is correct...I would expect the gauge to maintain the 32 reading once it stops pumping..

That is correct for every electronic fuel injection system I've ever heard of. Pressurized fuel may bleed off via injectors, pressure regulator, or check valve(s) in the pump. If left long enough, ALL such sytems WILL lose this residual pressure. Yes, the pump can typically run 3-5 seconds (if you wait before turning to START) and turns OFF. This repressurizes the system.

#35

I think I will double check the other components to be positive it is the fule pump...

But this is looking to me like the fuel pump check valve is bad. I have ZERO pressure when that pump stops.

FSM Pages EF & EC-18 wrote:The check valve prevents abrupt drop of pressure in the fuel pipe when stopping the engine.

#36

Ben, you don't need me, you have the FSM!

My personal spec is that I like the FP to remain above 1/2 of idle pressure for more than 20 minutes after shutdown.

I have a spare '83 gasser fuel pump sitting on the floor here in the shop. If you want to borrow it for a while, you're welcome. It is currently untested.

If you can put your gauge on the output of the fuel line that comes up to the fuel rail from the pump (and that's not always possible), you can quickly check if the FP check valve is the problem, and you'd probably want to source a replacement locally.

While the FP check valve is one item that goes bad, don't discount the possibility that the FPR is the culprit.

Can you "vise grip" the return line? If so, and you have a helper, apply the vise grip or equivalent (there does exist a hose pinch tool, I have one around here somewhere) just before your helper turns off the Ign. That's the quick check of the FPR.

#37

I was going to test the FPR as indicated in the FSM with my vac. pump tomorrow.

Al wrote:If you can put your gauge on the output of the fuel line that comes up to the fuel rail from the pump (and that's not always possible), you can quickly check if the FP check valve is the problem

The gauge is between the fuel rail and the filter. Do you mean here or at the tank, where the output line comes out of the pump and into the hard line?

Thanks for the offer of help Al. I think that once I check the FPR and *maybe* try to put that gauge near the tank to determine that the pump is indeed bad - I will just replace the pump with a new one.

Would anyone recommend dropping the tank and replacing the in-tank screen at the same time? Seems like a hell of a lot of work, but it was recommended on the Zcar forum when replacing a fuel pump...

#38

83_maxima wrote: The gauge is between the fuel rail and the filter. Do you mean here or at the tank, where the output line comes out of the pump and into the hard line?

Thanks for the offer of help Al. I think that once I check the FPR and *maybe* try to put that gauge near the tank to determine that the pump is indeed bad - I will just replace the pump with a new one.

Would anyone recommend dropping the tank and replacing the in-tank screen at the same time? Seems like a hell of a lot of work, but it was recommended on the Zcar forum when replacing a fuel pump...

I wouldnt reccomend dropping the tank and doing all that crazy stuff, its probably good to clean the sock, but the work involved might not be worth it. If the FPR is good, the pump check valve would be bad, not the pump itself. Its a little UFO shaped object that is connected inline to the pump and the fuel line under the car by itty bitty hoses.

#39

kassim503 wrote: If the FPR is good, the pump check valve would be bad, not the pump itself. Its a little UFO shaped object that is connected inline to the pump and the fuel line under the car by itty bitty hoses.

I am confused by this...

The FSM indicates that the fuel pump outlet has a check valve in it (FSM pages EF & EC-18 ). I first came to the conclusion that it was this that had failed (I still think it may be).

But on page FE-8 in the FSM, it shows the fuel check valve near the tank. This appears to be connected to the return line and it's only purpose is to prevent fuel from coming UP the return fuel line. This is what it's purpose appears to be to me. Last night I came to the conclusion that THE check valve was not the issue - rather the check valve that is in the outlet of the pump.

**edit: it appears that the fuel check valve is connected to the evaporation tube on one end and the tank on the other.**

Any other opinions?

I was probably going to get this pump ordered today, so I can get it in ASAP.

#40

First, Ben, Thanks for providing the FSM page numbers, saved a good deal of time.

83_maxima wrote:The FSM indicates that the fuel pump outlet has a check valve in it (FSM pages EF & EC-18 ). I first came to the conclusion that it was this that had failed (I still think it may be).

But on page FE-8 in the FSM, it shows the fuel check valve near the tank.

That check valve (on FE-8 ) is part of the evaporative emissions control system. It's there to prevent fuel vapours from escaping (vapours are supposed to go to the carbon cannister for temp storage), and to prevent a vacuum from forming in the fuel system when the temperature of the fuel/air in the tank decreases.

It lets air in the tank without letting air/fuel out.

A review of the L24e fuel pump:

The big Qs are:

Does the replacement fuel pump come with a replacement check valve? Nissan does not list the check valve separate from the FP.
Are you certain that it's the check valve that's the culprit?

A leaking FPR would give you exactly the same symptom as a faulty pressure check valve at the FP.

I was going to test the FPR as indicated in the FSM with my vac. pump tomorrow.

That test if for regulation, not for leakage.

I can't find a picture of the FPR and its connections in the FSM, but if you can pinch off its return-to-tank line just a moment before turning off the Ign. (requires a helper), you can see if that changes the symptom. If not, I'd go for a pressure check valve. If yes: bingo, it's the FPR leaking.

#41

My bad!

Bad memory has gotten the best of me, and I forgot that the check valves are built into the pump.

I really thought the check valve was free standing somewhere between the damper and the pump, after seeing al's pics my memory got re-jogged and I wound up with what it really looks like.

If you are replacing the pump, make sure you buy a quality unit-
http://www.napaonline.com/masterpages/N ... Line+Type)

http://www.napaonline.com/masterpages/N ... Tank+Type)

http://www.napaonline.com/masterpages/N ... Tank+Type)

I had trouble with the top 2 pumps, also installing them are kinda difficult because they give you this rubber sleeve and you have to use a bunch of stuff you find around the garage to even get the pump to have a tight fit in the bracket.

I tried using the url- it didnit work and im just too tired to figure it out, ill try re-doing it later

#42

First, THANK YOU Al and Kassim for the information.

Al, the break-down of the fuel pump is AWESOME. I was under the impression that the pump's check valve was internal. The picture clarified that for me. I'd like to have one of those assemblies as a back up. I may try to make it to the JY tomorrow and grab that and a few other things off of the 82 if it is still there...

As of right now, I am no longer certain that it is the check valve. The reason being: #1) TODAY, after starting the car, idling shortly, and shutting it off, it is now retaining pressure - 35-38 lbs. at the gauge, when off. It will also hold that pressure for quite a while. #2) I decided to take the car out today for a long drive, stop for a few minutes (15-20) and try to start it back up to re-create the issue and read the gauge simultaneously. As the car goes through it's regular routine - stumble, stumble, as I then juice the throttle to keep it running...FP is constant - 37-38 as I am revving the engine and 32-34 as it stumbles and nearly dies.

I am confused at this point. I may try to enlist my helper today and check the FPR. I do have a spare, but the one that is on the engine is newer.

#43

If you're going to go with a new pump from nissan, I suggest using the 280zx turbo pump.....especially if you intend to make more power in the future.

Just make sure you take the entire fuel pump mount out so you can duplicate the orientation of the old one with the new one.

If you don't use a damper, you will hear this pump louder than it should be.

Also........these cars fail to pick up fuel very well below 1/4 tank and starving these pumps is pretty hard on them if done enough times.

#44

asavage wrote:I have a spare '83 gasser fuel pump sitting on the floor here in the shop.

It was bad. When I tried to fire it up, it will run but not pump, even force primed. That's probably why that car got scrapped

Before I tossed it on our scrap pile, here's pics I took of a trouble point just waiting to be rediscovered. First, to review:

Now, the hidden trouble spot: Inlet strainer.

#45

didnt even know there was a inlet strainer in there, and its mighty small

NissanDiesel Forums

Rough running when hot

Who is online