fyanrudger Posted January 6, 2014 Share Posted January 6, 2014 Went on a spirited canyon drive on New Year's day with some friends and started experience a fuel pressure issue half way through the morning. Car began bucking/wanting to die/dying at cruising RPMS, but was find at WOT and above 3.5/4k rpms. Fuel pressure gauge is usually ~5psi, but I noticed it was sitting at ~1psi and would even die at idle. If I go downstairs and start the car right now, fuel pressure will be normal again, so I assume this has to do with the hard driving/heat. Is this a premature sign of a failing fuel pump (running a Carter 4600hp) or a vapor lock issue? No return fuel line and the line is routed down the tunnel, but not close to the exhaust at any point. Thanks! Dirty engine photo: Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted January 6, 2014 Share Posted January 6, 2014 Have you checked the Fuel filter near the tank for debris? Could have knocked some loose in the turns Quote Link to comment Share on other sites More sharing options...
fyanrudger Posted January 7, 2014 Author Share Posted January 7, 2014 I haven't. Wouldn't a clog be ruled out by the hot/cold issue? Quote Link to comment Share on other sites More sharing options...
ThreeEightyZ Posted January 14, 2014 Share Posted January 14, 2014 (edited) Are you sure that your pressure gauge is good? As well as your regulator? If it pulls fine when you roll on the throttle or at wot you are most likely running rich. It sounds just like when a bowl starts to flood from a float problem or too much pressure. Actually...i just looked at the picture...you're running a Mr Gasket gauge from the parts stores. Those are useful when you need them immediately...but they are JUNK. I have one on my car and I have gone through 4 of them in a year because after a month or so they stop reading even REMOTELY correctly. I actually just changed one last week because I was having this exact problem..turned out my actual fuel pressure was 12+ when the MG gauge was reading 5. Edited January 14, 2014 by ThreeEightyZ Quote Link to comment Share on other sites More sharing options...
fyanrudger Posted January 14, 2014 Author Share Posted January 14, 2014 Are you sure that your pressure gauge is good? As well as your regulator? If it pulls fine when you roll on the throttle or at wot you are most likely running rich. It sounds just like when a bowl starts to flood from a float problem or too much pressure. Actually...i just looked at the picture...you're running a Mr Gasket gauge from the parts stores. Those are useful when you need them immediately...but they are JUNK. I have one on my car and I have gone through 4 of them in a year because after a month or so they stop reading even REMOTELY correctly. I actually just changed one last week because I was having this exact problem..turned out my actual fuel pressure was 12+ when the MG gauge was reading 5. I don't believe it's the gauge, as the car is actually dying when the gauge is reading ~1psi and adjusting the gauge when cold brings the psi up or down...although adjusting it while hot (while I was having the issue) did not bring the pressure up at all, which led me to believe it's the pump. Quote Link to comment Share on other sites More sharing options...
fyanrudger Posted January 14, 2014 Author Share Posted January 14, 2014 I don't believe it's the gauge, as the car is actually dying when the gauge is reading ~1psi and adjusting the gauge when cold brings the psi up or down...although adjusting it while hot (while I was having the issue) did not bring the pressure up at all, which led me to believe it's the pump. After thought, would heat/prolonged driving time cause the adjuster to act differently/allow different fuel pressure when cold and hot? I know some are oil-filled, so they read differently, but the car generally runs fine. Unfortunately, I tore the car down shortly after I made this post to do floorboards/rails, so I can't drive it to diagnose for another week or so. Quote Link to comment Share on other sites More sharing options...
ThreeEightyZ Posted January 14, 2014 Share Posted January 14, 2014 (edited) After thought, would heat/prolonged driving time cause the adjuster to act differently/allow different fuel pressure when cold and hot? I know some are oil-filled, so they read differently, but the car generally runs fine. Unfortunately, I tore the car down shortly after I made this post to do floorboards/rails, so I can't drive it to diagnose for another week or so. Yes, fuel pressure should always be set at running temp, but i dont see that making a that significant of a difference. The part that doesn't fit the "low pressure" hypothesis is that you said at higher rpm and wot it runs fine. If it were truly running out of gas and you opened up the butterflies...the engine would likely hesitate and backfire or just stall instantly. I've had junk get caught in the my secondary bowl's float needle seat before and it cause almost the same symptoms...after i drove it for a while it would start to gargle when cruising. But, If i went WOT or rolled into the gas slowly it would be fine...then it would die at idle. After a minute of sitting it would fire right up and be perfect again. It was keeping the needle open and allowing the fuel pump to flood the bowl, pushing gas out through the venturis. Even if your gauge is correct...if the running pressure is low enough I can see the pressure dropping because it's not getting enough resistance from the floats. If the car didn't rev and go WOT fine I would say to check that the pump has a proper feed (gravity)...those pumps only like to push, not pull. Edited January 14, 2014 by ThreeEightyZ Quote Link to comment Share on other sites More sharing options...
fyanrudger Posted January 28, 2014 Author Share Posted January 28, 2014 Even if your gauge is correct...if the running pressure is low enough I can see the pressure dropping because it's not getting enough resistance from the floats. If the car didn't rev and go WOT fine I would say to check that the pump has a proper feed (gravity)...those pumps only like to push, not pull. Revisiting because the car is almost back on the road and I'd like to track down the issue. When I let the car idle the next day (engine was warm), I was able to adjust the fuel pressure up...I wasn't able to do that when I was having the issue. So, assuming the lack of resistance from the floats is the issue, what would the culprit be? Blown fuel regulator? Sunken float? Needle open? Quote Link to comment Share on other sites More sharing options...
ThreeEightyZ Posted January 28, 2014 Share Posted January 28, 2014 Revisiting because the car is almost back on the road and I'd like to track down the issue. When I let the car idle the next day (engine was warm), I was able to adjust the fuel pressure up...I wasn't able to do that when I was having the issue. So, assuming the lack of resistance from the floats is the issue, what would the culprit be? Blown fuel regulator? Sunken float? Needle open? Any of those..the most common thing would be a float problem though. The float could be saturated, something may be stuck in the needle seat, etc. Does your carb have sight glasses in the side? Quote Link to comment Share on other sites More sharing options...
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