THUNDERZ Posted May 27, 2004 Share Posted May 27, 2004 I HAVE A 260Z WITH A 1980 L28 AND TRIPLE DELLORTO 40MM'S. I AM RUNNING A HOLLEY BLUE PUMP W/REGULATOR. THIS PROBLEM HAS KEPT MY Z IN THE GARAGE FOR MONTHS NOW. THE CAR RUNS FOR ABOUT 5 MINUTES AT CORRECT FUEL PRESSURE(3.5) AND THEN SLOWLY DROPS OFF THE SCALE. I THOUGHT IT MAY BE A CLOGGED TANK OR LINE. I DROPPED THE TANK AND IT WAS SPOTTLESS. I BLEW OUT THE LINES ETC. I RAN A TEST WHERE I PUT THE PICK UP AND RETURN LINES IN A 5 GAL. BUCKET(TO ELIMINATE THE TANK AS A SUSPECT). STILL DID THE SAME THING. THE PUMP IS NEW AND JUST IN CASE I RAN A SPARE PUMP IN THE SAME TEST AND IT REACTED EXACTLY THE SAME. ANOTHER INTERESTING DETAIL IS THAT RIGHT AROUND THE SAME TIME THE PRESSURE STARTS TO DROP, THE RETURN LINE STARTS TO BLOW A FEW BUBBLES IN THE BUCKET OF GAS. THAT WOULD MAKE ONE THINK IT MIGHT BE PULLING IN AIR BUT FROM WHERE? THE ONLY PLACE THAT THERE MAY BE SOME VACUUM WOULD BE IN THE FEED LINE AND THAT IS SNUG. TAKE A STAB AT IT! :malebitchslap: Quote Link to comment Share on other sites More sharing options...
technicalninja Posted May 27, 2004 Share Posted May 27, 2004 Does the symptom stay the same regardless if engine is running? Have you checked amp draw on pump as pressure bleeds off? What you are describing is a pump pick up restriction or a pump heating up and failing. Two different pumps usually rules out pump failure. Running pick up hose into gas can usually rules out pick up restriction. Were you using same pick up hose to tank for the gas can test? Maybe weird internal damage to hose. Truly strange. Please post when you figure out what problem is. Maybe resistance of pump feed wiring or bad ground causing problem? Quote Link to comment Share on other sites More sharing options...
wheelman Posted May 27, 2004 Share Posted May 27, 2004 Good point TechnicalNinja, try running the pump connected directly to a battery to eliminate the wiring in the car. If that doesn't get rid of the problem try running each pump connected directly to a battery and just run an input line and a return line and see if the pressure drops. In other words bypass each part of the system in the car until the behavior disappears. Wheelman Quote Link to comment Share on other sites More sharing options...
DaleMX Posted May 27, 2004 Share Posted May 27, 2004 Maybe a fuel line is too close to the exhaust somewhere and is creating vapor. Good luck finding the gremlins. Dale Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 27, 2004 Share Posted May 27, 2004 Pressure regulator part of the fuel pump. Quote Link to comment Share on other sites More sharing options...
THUNDERZ Posted May 27, 2004 Author Share Posted May 27, 2004 Pressure regulator part of the fuel pump. Not sure what you mean...I have a pressure regulator....I dont think the pump is adjustable and I have had the same results with two completely different pumps. : Quote Link to comment Share on other sites More sharing options...
THUNDERZ Posted May 27, 2004 Author Share Posted May 27, 2004 Maybe a fuel line is too close to the exhaust somewhere and is creating vapor. Good luck finding the gremlins.Dale All the testing that I am doing now is out of a 5 gal. bucket so the fuel lines arent next to anything hot. Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 28, 2004 Share Posted May 28, 2004 I you are running at a constant speed and your fuel pressure drops then it is one of the following: 1) the fuel pump is screwing up and either not pumping or not getting suction properly (cavitating) Air bubles would be an indication of that. 2) The fuel pressure regulator is screwing up. It is a spring/diaphragm type? Maybe there is a hole in the diaphragm or the spring is screwed up. (air bubles could be an indication of air coming inthrough the pressure regulator) Then again - where are you measuring the fuel pressure? A guage generally only measures pressure downstream from its location so look at stuff AFTER the gauge to see if there is a problem there. Quote Link to comment Share on other sites More sharing options...
brokebolt Posted May 29, 2004 Share Posted May 29, 2004 Yes, bubbles in the return line going into the bucket would suggest air in the fuel lines. Do the same bucket test but only run the pump leave the car engine off. This will make a conditon where no fuel is removed from the lines. If you duplicate the same results than I would think there is residual air in the fuel lines. The pump is prossibly cavitating and thus drop in fuel pressure and bubbles in the return line. The Holley Blue pump is a rotoray vien pump and requires fuel to seal the viens to provide fuel flow and pressure. This is also a good test to see just how well your needles and seats are sealing. If the fuel floods the bowls than the needle and seats are worn and/or the pressure is excessive (you did say nice low pressure @ 3.5). This test is good to check the fuel bowl level aswell. Mike Quote Link to comment Share on other sites More sharing options...
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