z or bust Posted July 20, 2008 Share Posted July 20, 2008 Ok I have a 77 280z all stock. What happens is it will un fine everything thing is fine then the fuel pressure will drop down to about 15-20 psi. It will run like this for a minute or so then will hop back up suddenly and be at about 50-55 psi then go back to normal. I have replaced the afm, fuel pump, checked my connections, and still am stumped. Has anyone else experienced this problem? My thughts are that there might be debris in the tank (the car has sat for about a year) and it will clogg the system temoparily then push past or move causing the sudden spike in presssure. Does this sound reasonable. Anyone have any thoughts? Quote Link to comment Share on other sites More sharing options...
z or bust Posted July 20, 2008 Author Share Posted July 20, 2008 I got to thinking and could this be the fpr? Which would explain the spike in fuel pressure? Quote Link to comment Share on other sites More sharing options...
Doc Hawk Posted July 20, 2008 Share Posted July 20, 2008 The fuel pressure regulator is a fairly common point of failure, and the symptoms fit. Did you replace your filters, too? Lastly, how are the little bits of hose on and around your fuel rail? I rebuilt a 280 last year and the injectors and rail were all fouled up with little bits of rubber from the interior walls of the small connector hoses. They looked poor to fair from the outside, but inside they were truly junk. Quote Link to comment Share on other sites More sharing options...
z or bust Posted July 20, 2008 Author Share Posted July 20, 2008 Yeah its worth a shot trying the fpr. I have an aftermarket reg and the aluminum fuel rail so i'll probably just do that that way I can eliminate all those little lines like you were talking about. Thanks for input! Quote Link to comment Share on other sites More sharing options...
z or bust Posted July 21, 2008 Author Share Posted July 21, 2008 Update: I installed an aluminum fuel rail with adjustable fpr, new injectors. I blew air through the fuel filter to make sure it wasn't clogged and its good. What happens is a start i up and it runs fine for only a minute with great fuel pressure. Then it suddenly drops down to only about 8psi (as i had stated before) and will not reutrn to regular pressure. If I wait a an hour or so until everything cools down it does this all over again, great presure for only a minute. Could it be that the fuel pump is bad and once it gets hot from running it starts to slow down? By the way there is plenty of gas in the tank. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 27, 2008 Share Posted July 27, 2008 What is in your tank? Got something blocking the pickup tube? Blowing air through a filter doesn't confirm it's 'good', either. Simply replace the filter. That's a cheap bit of insurance. I am still trying to figure out why the AFM got swapped for a Fuel Pressure Issue. What you stated before was it was at 15-20psi then jumps to 50-55. That is a big difference from 8...and what is the upper end of the pressure now? The pump bypasses at 60psi...and that's usually around 50-55 at the rail due to pressure drop. I'm thinking a plugged fuel filter, restricted hose, or intermittently plugged return line will cause the jump to 50-55, but the drop to 8 (or 15-20) may simply be a result of the relief valve in the pump not reacting quick enough to something releasing it's restriction. What FPR is on it, what is it set to, what pump are you using now if you 'replaced it', and why did you swap to an aftermarket rail with 'new' injectors before finding out what was causing the fuel pressure problem. Anything you have changed can possibly compound your initial issue, and lead to new issues unrelated to the first...which you may be experiencing now. Best to fix one thing at a time till you know it's good, then modify. Quote Link to comment Share on other sites More sharing options...
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