noelawinslow Posted April 23, 2015 Share Posted April 23, 2015 Hey all, picked up an NA auto z31, trying to track down a hard start and misfire condition. Checked fuel pressure just after the filter and it kept shooting down to 0 after I shut it off, so I crimped off the return line, primed the system, and crimped off the supply line. Still bleeds out. Replaced FPR. Fuel pressure stable at 60 psi at idle. Much too high. Holds pressure long enough to watch the needle drop now though. Pulled the evap check valve. One way it slowly releases air and the other way it lets out plenty, so apparently that's good. I hooked up an air compressor to the return line, wondered if that might jack up the pressure, blasted air through it at 5psi at first, no issue. Moved up to 60 psi and there's no blockage. Might as well clean the supply side out too but now I'm kinda out of options unless I want to check the Evap system further. I didn't think evap could cause problems like that. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 23, 2015 Share Posted April 23, 2015 The fuel probably went back the way it came. Quote Link to comment Share on other sites More sharing options...
noelawinslow Posted April 23, 2015 Author Share Posted April 23, 2015 What does that even mean? Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 23, 2015 Share Posted April 23, 2015 It flowed backward, from whence it came, when the fuel pump stopped spinning. Quote Link to comment Share on other sites More sharing options...
noelawinslow Posted April 23, 2015 Author Share Posted April 23, 2015 I thought the system was supposed to retain pressure with the engine off. I cleared the lines and started the car up again, 60 psi still and it barely idles. I'll run a return line to a gas can and see how that works for me. Is it safe to run compressed air through the return line in the tank with the fuel cap off? Quote Link to comment Share on other sites More sharing options...
noelawinslow Posted April 23, 2015 Author Share Posted April 23, 2015 Fuel dribbles out the FPR return when routed to the fuel can, but I'm still getting a solid 60 psi. Crimped off the supply line after priming and fuel still loses pressure. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 23, 2015 Share Posted April 23, 2015 There's a check valve in the pump. They fail sometimes. Crimp the supply line before it leaks down and see what happens. You didn't say anything about what the pressure was before you replaced the FPR but the fact that fuel dribbles from the FPR instead of flowing could mean that the FPR is blocked or defective. If you knew what it was before it would give a pretty clue about blockage versus FPR. Some aftermarket FPR's can be connected backwards and will give full fuel pump pressure in the rail if that's done. I'm not familiar with the Z31 fuel system in general beyond the basics, besides the fact there are 6 years worth of them. There may be differences. Give some details on yours. Think in terms of pressure instead of flow direction. Pressure works backward too. Quote Link to comment Share on other sites More sharing options...
noelawinslow Posted April 24, 2015 Author Share Posted April 24, 2015 My bad, the pressure was 60psi idle before I replaced the fpr. Signs keeps pointing to it's still bad so I'll go get another one. This regulator can't be installed backwards very easily, it has two supply lines for the rail which orient it. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 24, 2015 Share Posted April 24, 2015 Don't forget to check the gauge. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 24, 2015 Share Posted April 24, 2015 You might also measure pressure with the FPR not installed. Just to be sure there's not something blocking the ports. The FPR is just a pressure relief valve. If you don't have some monster fuel pump pushing so much fuel it can't bleed off pressure, it should work if the flow paths are clear. Quote Link to comment Share on other sites More sharing options...
noelawinslow Posted April 26, 2015 Author Share Posted April 26, 2015 I'll put the gauge on my truck today and see if the gauge reads out well. The gauge is also new. Quote Link to comment Share on other sites More sharing options...
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