dat620_73 Posted May 16, 2019 Report Share Posted May 16, 2019 I have a question about fuel pressure. I have a pressure gauge inline between the manual pump and Weber carb, at idle or acceleration the gauge needle fluctuates rapidly, so hard I can hear it bang off the needle rest! Is this normal, I don't think that is normal. Is this a sign the pump is going out? Quote Link to comment
john510 Posted May 16, 2019 Report Share Posted May 16, 2019 If it runs fine i would guess it's the gauge that's gone bad.Is it one of those oil filled gauges ? Quote Link to comment
dat620_73 Posted May 17, 2019 Author Report Share Posted May 17, 2019 It's not oil filled, and after 2 hours of sitting the fuel pressure drops from 4 psi to 0. I could have sworn that when I first installed the gauge the needle was relatively stable. Today it started to act like I was letting the clutch out to fast and a complete loss of power at high rpm 3000-4000, almost like the brake is on. It's a 73 620, with a stock 1600, Weber carb, new fuel filter, plugs cap, rotor, wires, pertronix, 4 speed trans and 14" tires that's why I'm at such a high rpm. 3500 is about 55mph Quote Link to comment
5t341tH Posted May 17, 2019 Report Share Posted May 17, 2019 hows the quality of that gauge? you only want oil filled gauges 1 Quote Link to comment
dat620_73 Posted May 17, 2019 Author Report Share Posted May 17, 2019 Oh ok I'll get an oil filled gauge. Cool trucks fixed Quote Link to comment
G-Duax Posted May 17, 2019 Report Share Posted May 17, 2019 Pulsations are because of mechanical fuel pump.... No way around it, because big diaphragm goes up & down once every 2 engine revolutions. Oil filled will do little. Pulsations will still kill the little brass gears inside of any gauge. Oil filled gauges are more for high frequency vibrations induced by the machinery your gauge is attached to, in this case, your truck. You need a ' gauge snubber '. Available at any industrial supply, or hydraulic dealer. (40 years of hydraulic/pneumatic back ground here) 2 Quote Link to comment
dat620_73 Posted May 17, 2019 Author Report Share Posted May 17, 2019 So here's the update. I replaced the mechanical fuel pump with a new mechanical fuel pump. The fuel pressure gauge stays steady at 4psi and the truck runs great again. 2 Quote Link to comment
banzai510(hainz) Posted May 17, 2019 Report Share Posted May 17, 2019 what brand pump? cost? Quote Link to comment
dat620_73 Posted May 17, 2019 Author Report Share Posted May 17, 2019 Precision from O'Reilly's. $32.35 with tax. Quote Link to comment
Stoffregen Motorsports Posted May 22, 2019 Report Share Posted May 22, 2019 I wonder if the spring was going bad, causing the fluctuation. As Duax said, mechanical pumps cause the needle to jump. I'll try the gauge snubber next time. Quote Link to comment
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