Fuel Pressure 26PSI

[sblake01]

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, 2009 by sblake01

[ZBob]

Bobs77, Have you had any luck with your start problem. My 78 280z is doing the same thing. IE during hot summer months, its hard to start after it has been running and then shut down for about 10 minutes. I have notice the temperature while running is about 170-180 degrees. Once shut down the engines temp slowly increases to about 210 degrees and this is when it starts being difficult to start. Once the engine temp drops back to aobut 170-180 then it will start normally. I feel like the increase in temp is affecting something but not sure what it may be. IE Could the increase in temp cause the metal fuel injection line to heat up and increasing the pressure in the line?

[ChrisB77]

You are right Stephen that you haven't read this anywhere. In fact, I didn't either. Wise old mechanic shared it with me and has proven to me to be a good test of the fuel pressure regulator. I'll share with you what was shared with me. If it proves to be faulty or incorrect, my apologies. Ok here's what I believe to be true. The FPR maintains the correct pressure by controlling the amount of fuel that is returned to the tank. Spring pressure against the diaphragm in the FPR completely blocks off the return line when the pressure is lower than regulated. As fuel pressure increases to 36 psi in this case, the pressure overcomes the spring and fuel is allowed to return. In this way, a constant pressure in maintained. When we pinch the return line, this confirms that the pump is indeed capable of producing more than enough pressure to overcome spring pressure. If the fuel pressure is really low, then the spring must be slightly weak allowing fuel to return to the tank when it shouldn't.

I hope I'm being helpful here and not giving incorrect or incomplete info.

[sblake01]

I just don't think that would indicate a faulty FPR. By pinching the line, you're actually bypassing the regulator, at least that side of it. The FPR actually uses intake manifold vacuum and the pressure from the fuel pump and creates a differential pressure between the two (36.3 psi). Pinching the return line would naturally cause a rise in the pressure reading just by the nature of how the FPR works. Think about it.

[bobs77]

Thanks for the feedback Stephen. Outside of this one issue the engine runs fine--starts quickly every time (even though the fuel pressure only goes up to 32psi, and drops to zero within a few hours of shutting the engine off), runs smoothly and doesn't over heat. I'll continue to work on this but won't lose any sleep over it.

[bobs77]

Don't mean to beat this dead horse again, but I wanted to find out if I'm asking too much or did I just get a jerk at Courtesy Nissan.

I bought a new FPR from Courtesy, installed it and instead of the fuel pressure increasing to 36.3 psi, it dropped to between 26 and 30. Thinking I got a defective FPR I called Courtesy and was told I'd have to take the car to a local dealer to have it tested. And, oh yeah, I may get charged for the test.

Before I call the Parts Manager at Courtesy I wanted to find out from you guys if asking them to replace the FPR without getting it verified at the local Nissan dealership is asking too much, or was the parts guy at Courtesy trying to blow me off. (The FSM is pretty straight forward about it--if the pressure is below 36.3 psi, replace the FPR.) If the pressure is even lower after the replacement the new part is defective. I buy all my parts from them and haven't had problems in the past. I know they support the Z community, but the attitude of the guy I talked to is making me re-think that.

Thanks

[sblake01]

Is there anyone at your local Nisan dealership that is familiar with Datsuns? I know it sounds like a strange question but I know from talking to the guys here at Nissan of San Bernardino that it wasn't too tough for me to determine that none of the technicians there really know much about them. If I had tested the FPR and found it faulty, I'd be insistent with the parts manager about replacing it, without further testing.