Low Fuel Pressure - electric fuel pump

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Tjhoward84

Tjhoward84

1969 Barracuda Convertible
Joined
Mar 19, 2014
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Bothell
I've got a potential issue with my fuel pressure. At the guage mounted inline with the fuel line to the carb, the pressure is reading 1.5 psi. The engine just quits while sitting at a red line but not all the time. However, it goes down the road just fine. We originally set the fuel pressure at 6-6.5 psi and it never quit at red lights. I don't know how it is now only getting 1.5 psi since we have not done any modifications or adjustments to the fuel system. The car is running an electric fuel pump and then goes into a Summit Racing fuel regulator then thru a fuel filter and then to the carb (750 Holley Double Pumper). The engine is a Magmun Performance crate 360. To make matters more wierd, we tried adjusting the fuel pressure at the regulator by turning the adjustment screw out but nothing happened. We even tried turning the screw in all the way to reduce the fuel pressure to zero (0) but it never changed from the 1.5 psi reading on the guage.

I'm wondering if there is something in the fuel pump that is keeping it from openin more or closing?

Thoughts???
 
did you try to by pass the regulator and see what the pressure is?
 
i really like the street/strip carter mech. pumps,plus they can be rebuilt.just saying.seems like everyone is using the electrics these days.
 
What brand of electric pump are you using? Some pumps have an internal pressure/bypass valve.
-Matt
 
i had the same problem so i got a 392walbro a bypass regulator and put a return line on . i set my fp to 7psi and it is rock solid .
 
Check fuel filter first. Don't throw money at it.
 
Louie70Dart said:
Check fuel filter first. Don't throw money at it.
Click to expand...

The fuel filter is between the regulator and the carb. It's brand new. I'm thinking it's the regulator. It's a Holley regulator (PN 12-803BP) with a return line back to the tank.
 
zombywoof said:
did you try to by pass the regulator and see what the pressure is?
Click to expand...

Probably don't want to do that since I'd be running straight from the fuel pump (unregulated) time the carb. The fuel pump puts out 30 psi to the regulator. Don't want to dump that much fur pelt to the carb.
 
Basics,
What type of fuel pump?
Where is it mounted?
Have you checked voltage at the fuel pump?
Have you taken any readings right off the fuel pump, both pressure and flow?
Do you know for sure the gauge is accurate?

My .02 is that if you truly had 1.5 psi or 6 psi sitting at a light idling, either one wouldn't matter, you are using hardly any flow of gasoline and the bowl should be pretty much full not causing a idling issue. Especially if it runs down the road just fine when you are using a much greater volume/flow of gas.
It might be something other than fuel pump like the carb. is flooding out when idling.
 
Have you tried a diagnostic pressure gage? Disconnect the lines from the carb and run them into a bucket. Run the pump and check the pressure with a good gage (or known good gage). Then set the regulator to what you want. Also if it's on the engine, move ther egulator to the bodywork. Sometimes vibration can bother the settings.
 
nothingbutdarts said:
Basics,
What type of fuel pump? - electric, don't know the manufacture or model number.
Where is it mounted? - on the inside frame rail under the rear passenger seat area
Have you checked voltage at the fuel pump? - No, but I know it works because it's pretty loud and when it was producting 6% psi, it sounded the same as it does now.
Have you taken any readings right off the fuel pump, both pressure and flow? - No, hard to do since the car is fairly low and I just sold the car lift. Will probably have the speed shop do that.
Do you know for sure the gauge is accurate? - Don't know for sure but it's been faily accurate up until lately.

My .02 is that if you truly had 1.5 psi or 6 psi sitting at a light idling, either one wouldn't matter, you are using hardly any flow of gasoline and the bowl should be pretty much full not causing a idling issue. Especially if it runs down the road just fine when you are using a much greater volume/flow of gas.
It might be something other than fuel pump like the carb. is flooding out when idling.
Click to expand...

I agree with your assessment of the carb flooding out - I never thought of that. I does go down the road without any hesitation. One would expect that if it dies at idle, it would die while turning 2,500 rpm down the road too. It also idles really low at 400 - 500 rpm.
 
Found the information on the fuel pump. It's a Facet PN 40104. It appears this pump only outputs 1.5 to 4.0 psi. Since we have 1.5 psi at the fuel pressure guage next to the carb, the other 3 psi is probably getting dumped back to the tank via the bypass port.

Does the engine need more than 1.5 psi of fuel? If so, I guess I'll be replacing the fuel pump.

Thoughts????
 
That pump is barely big enough to feed a lawn mower... Get a mallory 140 or similar.

25gph isn't going to cut it!
 
crackedback said:
That pump is barely big enough to feed a lawn mower... Get a mallory 140 or similar.

25gph isn't going to cut it!
Click to expand...

That's too funny. I had a good laugh at that one.

I'm having it changed out.

Hopefully that will solve my problem along with one more carb/idle tuning session.
 
Cool. 25gph and 4 psi isn't a good set up for a decent v8 engine.

Get the ignition timing sorted out from idle/initial perspective. A lot of carb issues at idle and through transition are rooted in that setting.
 
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