Fuel Pressure 26PSI

[DatsunZsRule]

I replaced the check valve in my stock pump ('77 280Z) and it still bleeds down. Fuel pressure is a little low at 32psi, not 36.3. It runs well most of the time, except on warm days when I try to re-start it after driving for a while. When it starts the idle speed is only ~600 and it runs rough. I have to bring the idle up to ~2000 for 10-15 seconds and then it's fine. I tested the regulator per the FSM and it passes, and there are no visible leaks anywhere so is this a sign the pump is showing it's age?

Does it reach 32PSI then slowly bleed to 0 or does it hold at 32PSI?

On the poor running issue during warm only after driving sounds related to a different problem. A common cause for a problem such as your describing is a faulty Water Temperature Sensor. Have you checked that? Usually a weak pump that causes running issues will be noticed all the time (Cold or Hot)

Edited May 28, 2009 by DatsunZsRule

[conedodger]

That fuel pressure can be a problem if you get the engine hot enough or have a hot enough ambient temperature. Then once you shut it off it can be hard to start. Sounds like things are still cool in Delaware...

[Walter Moore]

The club CD is much easier to use, but if you really need information here is another source:

http://www.xenons30.com/reference.html

[Z train]

Sounds like leaking injector(s).

[bobs77]

Thanks for the suggestions:

Does it reach 32PSI then slowly bleed to 0 or does it hold at 32PSI?

--It jumps up to 32psi when I start the engine. I checked it ~2.5 hours after I got home tonight and the pressure had dropped to zero.

On the poor running issue during warm only after driving sounds related to a different problem. A common cause for a problem such as your describing is a faulty Water Temperature Sensor. Have you checked that? Usually a weak pump that causes running issues will be noticed all the time (Cold or Hot)

--I replaced the Water Temp Sensor 4 years (5000 miles) ago.

Sounds like leaking injector(s).

--I had the injectors sonically cleaned and tested a couple years ago; no leakers.

[Z train]

Thanks for the suggestions:

--I replaced the Water Temp Sensor 4 years (5000 miles) ago.

Sounds like leaking injector(s).

--I had the injectors sonically cleaned and tested a couple years ago; no leakers.

Interesting.THe next time it has the "problem",insteading of waiting for it to clear up,let it run ragged for a minute or two and then shut it down and pull the plugs.If it is an individual cylinder you should be able to read it on the plug(s).

[DatsunZsRule]

I'm sure you've checked this already too, but are you sure there isn't a slight blockage in the lines/fuel filter or a kinked line somewhere?

I have seen many times people complaining about a poor starting/running issue after they have driven it around and if lucky, it's just a simple thing like a dirt fuel filter. The pressure decreases after running the car due to the "crud" getting stirred up and restricting the flow. Just another thought

[ChrisB77]

Just some thoughts from my own personal experience with cars. Fuel pressure bleed off after several hours is usually never a problem especially since you say it will start fine after that time. Even though the pressure gauge shows zero psi, the lines are still charged with fuel. When the pump comes on, the pressure immediately jumps up and the vehicle will start fine. If the pressure loss is too great and the fuel lines are draining back to the tank as would be the case with a bad check valve, the car would have extended cranking time but would start and run fine once the lines were filled with fuel again. As for your low pressure, the pressure regulator is the most likely failed part. On the passenger side on the engine bay there are two rubber fuel lines. One from the tank that has a filter and the other back to the tank from the regulator. If you pinch off the return line briefly with the engine running, the fuel pressure should go extremely high( about 60 psi I think). If the pressure goes up then the pump is ok and the regulator is bad. If not, then the pump can't produce anymore and should be replaced IMO

[chiefmd]

ChrisB77- The regulator is fairly new so I was assuming that it was the FP. I will confirm by performing the test you recommend. Thanks for you assistance.

[chiefmd]

Performed the test this morning and the FP jumped right up to 60psi. Guess I'll purchase a FPR.

[DatsunZsRule]

Not Disagreeing with the fact that you may have a bad FPR but losing fuel pressure is not acceptable either. It is suppose to hold at 36 constantly. If you don't want to believe me, read the F.I. section of the FSM.

Edited May 30, 2009 by DatsunZsRule

[bobs77]

Just some thoughts from my own personal experience with cars. Fuel pressure bleed off after several hours is usually never a problem especially since you say it will start fine after that time. Even though the pressure gauge shows zero psi, the lines are still charged with fuel. When the pump comes on, the pressure immediately jumps up and the vehicle will start fine. If the pressure loss is too great and the fuel lines are draining back to the tank as would be the case with a bad check valve, the car would have extended cranking time but would start and run fine once the lines were filled with fuel again. As for your low pressure, the pressure regulator is the most likely failed part. On the passenger side on the engine bay there are two rubber fuel lines. One from the tank that has a filter and the other back to the tank from the regulator. If you pinch off the return line briefly with the engine running, the fuel pressure should go extremely high( about 60 psi I think). If the pressure goes up then the pump is ok and the regulator is bad. If not, then the pump can't produce anymore and should be replaced IMO

I just installed a new Nissan FPR and started the car. The fuel pressure was 30psi; when I clamped the return line it jumped to 55. So this means the new PFR is bad?