I've been steadly working on a 77 280z that I purchased over the winter. Just replaced the injectors and she is running quite well. I went ahead and installed a inline fuel pressure gauge and am only getting 26 psi. When I shut it off she holds pressure for a few hours but eventually drops off to zero, also, no problem starting up after its sits with zero pressure. I installed a Fram G3 filter before the pump and it is clean. I was going to clean the filter in the fuel pump but it's not OEM. It looks like the one that Black Dragon sells. Any suggestions as to what else could cause low FP. Thanks

Edited May 26, 200915 yr by chiefmd

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...

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

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

Sounds like leaking injector(s).

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.

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).

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

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

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.

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

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, 200915 yr by DatsunZsRule

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?

Bob, I saw that also and I don't know where that test comes from. I waited to comment on that until I did some checking myself. Just before I sold my Z I checked it. The fuel pressure was in the the range it should be, roughly 36psi. I clamped the hose and the pressure went up. Ran the same test on the 810, same results. Pressure doesn't bleed off on either car. I actually think that test confirms that the FPR is functioning since you are basically bypassing it by clamping the hose. The only thing I see in the FSM as far as a functional test of the FPR:

Connect a fuel pressure gauge as outlined under Fuel Discharge Pressure Check, and check fuel discharge pressure. If a fuel discharge of 2.55 kg/cm2 (36.3 psi) is not obtained, replace pressure regulator.

The only test I know of that involves squeezing the hose is for the air regulator. I don't want to argue with ChrisB77's findings but my personal experience (at least 25 years) and everything I've ever read seems to contradict them.

Edited June 13, 200915 yr by sblake01