fp280z Posted August 15, 2005 Share Posted August 15, 2005 Here's the scenario: Triple Webers on an L28 with mods. Holley fuel pressure regulator with fuel pressure guage attached to one output port. Other output port attached to 5/16" hose going to carburetors. No return line. Input port is 3/8" hard line from a Carter rotary fuel pump mounted next to the fuel cell. Flip the fuel pump on (this is a racecar) and the pressure guage goes to 3psi. Start the car and the pressure remains steady at 3psi. Then, as the car warms up the fuel pressure will gradually drop down to 0psi. Car still runs and drives fine with the guage reading 0psi. Pinching the hose to the carbs causes the guage to deflect slightly. Anyone experience this before? Is this normal? What's up? BTW, I had the same pump/regulator setup when I was running SUs but the pressure guage is new with the Webers so I'm not sure if this was happening with the SUs... -Rick http://www.io.com/~rickm/fp280z Quote Link to comment Share on other sites More sharing options...
mark Posted August 15, 2005 Share Posted August 15, 2005 If the car runs properly at speed and under a load then I would bet you have a gauge problem. I ran a very similar set up on my 240 auto X car. Do you have a spare gauge? Quote Link to comment Share on other sites More sharing options...
srgunz Posted August 15, 2005 Share Posted August 15, 2005 I thought I was the only one with that problem. I have a 5 psi pump with the same holley regulator. It reads 0 psi and with the regulator wide open it reads about 1 psi. With the regulator wide open it also causes the carbs to run extremely rich. So it seems to be giving a false reading. Like yours the car runs great except when I cranked up the regulator thinking that was the problem. I emailed holly tech. to see if that spare port is ok for a guage. They said yes and that I must have a bad guage possibly. The guage is new as well as the pump and regulator. I have never heard of a fuel pressure guage being bad out of the box or even bad at all. I am stumped. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 25, 2005 Share Posted August 25, 2005 just a quick glance at this thread...but is it possible that the gauges can only measure static pressure? bernoulli's principle: as fluid velocity (flow) goes up, fluid pressure goes down... in theory it could be in the realm of possibility that your gauges are correct...which is why your car still runs...flow is happening... Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 6, 2005 Share Posted September 6, 2005 I have this same problem it'll start to bleed off to like 1psi. Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted September 7, 2005 Share Posted September 7, 2005 Maybe the pressure gauge is not that precise. There is a pressure gauge on my low tech tire pump, it reads 25 psi when my precision electronic gauge reads 31psi. It's not a fuel pressure gauge but you get the idea. Quote Link to comment Share on other sites More sharing options...
KUBO-Z Posted September 8, 2005 Share Posted September 8, 2005 Just a thought: Could your problem be the placement/connection location of your gauge? Where is it located? Quote Link to comment Share on other sites More sharing options...
Buzz Posted September 7, 2006 Share Posted September 7, 2006 I had the same problem with holly liquid filled gauge,try a gauge with out liquid.It seem that the heat from the engine made the liquid expand causing the gauge to read 0. I installed a air psi gauge and it worked fine. Mike 77 triple webers. Quote Link to comment Share on other sites More sharing options...
brokebolt Posted September 9, 2006 Share Posted September 9, 2006 With a dead head system it is possible to produce excessive wear on the pump thus low presures. As the pump warms up it is possible it will develop less pressure and you are getting more leakage in the pump. It should be a rotary vien pump for safety reasons and this type of pump also is excellent for moving fluid but not developing excessive presures and spikes. This type of pump uses the fluid to help seal the veins in the turit. If you use a open end system where a return line is used than you may be in the same situation with no pressure but you will have flow. You can benifit more from this system as you are always moving fuel in the pump which deminish the wear isssue (you will always have wear), and you can install a fuel cooler and help with performance by cooling the fuel and returning all the excessive amount of fuel back to the tank. I would guess that at such a low pressure your guage is not too accurate but I would definetely suggest using a return line. Hope this helps. Quote Link to comment Share on other sites More sharing options...
srgunz Posted October 10, 2006 Share Posted October 10, 2006 As a follow up to my comments, I removed the holly fuel pressure regulator. I took the guage off it and put a hose fitting on the guage. I wanted to see what I was getting at the furthest carb.,so I removed the hose at carb and inserted and clamped the guage on it. When I turned the pump on I get exactly 3-1/4 psi. Interesting because the pump says 4 - 5 psi. So on mine the regulator is in the tool box as it is not needed. It seems that the holly fpr and guage set up is not reliable for accurate readings. At least on mine. Your best bet is to actually check psi at carbs! Quote Link to comment Share on other sites More sharing options...
bjhines Posted October 11, 2006 Share Posted October 11, 2006 High velocity flow past the pressure port might be causing it to read low... I am using a holley red pump back at the tank... and I run a nice new mechanical pump as a redundant backup and regulator... all with the original fuel rail... .... Quote Link to comment Share on other sites More sharing options...
TBK Posted October 11, 2006 Share Posted October 11, 2006 Common denominator here appears to be the holly bypass type regulator, had same prob here! also running adiff elect pump at tank (cant rember brand) and mechanical on engine! with guage installed in regulator.am using the bypass port back to tank return. Quote Link to comment Share on other sites More sharing options...
Buzz Posted October 11, 2006 Share Posted October 11, 2006 It's probably the gauge!I had a liquid filled gauge and it did the same thing,I put in a standard air psi gauge and it worked fine.Of course the holly fuel pump dosen't!!runs good for about 30 min and then just stops pumping.I tried the return line with a bran new holly pump and that did the same thing.Holly crap pumps Quote Link to comment Share on other sites More sharing options...
fp280z Posted March 8, 2007 Author Share Posted March 8, 2007 Posting my "solution" just in case anyone comes across this thread and has the same issue. Buzz was right! It was the liquid filled pressure guage. Swapped it out with a non-liquid filled unit and pressure is rock steady even after the engine is nice and warm. Thanks. -Rick www.typeischeap.com Quote Link to comment Share on other sites More sharing options...
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