Typical Fuel Pressure?

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340inabbody

340inabbody

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So I am in the process of bringing my motor (340) up from a deep sleep after body restoration. I never had a fuel pressure gauge and decided to add one. I noticed at the start up cold the fuel pressure was initially 6 psi. After some minor changes in timing and idle and warm up it dropped to ~2.5 psi. From then on it stayed at ~2.5 psi regardless of idle/rpm.
It seemed to be running fine no stalling or anything. I’ll check the float heights when the motor cools down a bit….

I don’t know what caused the drop from about 5/6 psi down to 2.5?

Normal?
Oh and yes I am running a good pre-filter…

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Most of these gauges are junk so double check the gauge with another one. I’m guessing with all the rubber fuel line this car never hits the drag strip.
 
I’m going to replace the fuel filter first. Then if that doesn’t work try and do some type of output test.
 
I would consider changing that rubber line from the pump to the carb, they’re readily available in pre-bent steel for not much money. Stick pumps generally run in the 6psi range.
 
cosgig said:
I would consider changing that rubber line from the pump to the carb, they’re readily available in pre-bent steel for not much money. Stick pumps generally run in the 6psi range.
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What’s the rationale from changing rubber line to hardline? Is it potential loss of pressure due to expansion or is it reliability? It is a new line. Thanks.
 
340inabbody said:
I’m going to replace the fuel filter first. Then if that doesn’t work try and do some type of output test.
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That's reasonable. I would also replace ALL of the rubber hose in the fuel system with Gates Barricade EFI hose. Make SURE it doesn't just say Barricade. It has to say "EFI" on it to be the hose I am talking about. It's TOUGH and it's ethanol resistant. Remember, ALL means ALL, including from the tank sender to the hard line. I had that very piece on my truck soften up and was sucking closed on hard acceleration blocking fuel flow.
 
Meh,,,,,usually equates to something like :

“ I’m not exactly sure but from my experience I believe it is “,,,,,.
That’s why meh,,,is a lot less trying than all the other,,,lol .

To the issue,,,,are you using a stock pump or aftermarket ?
I used to use a Holley Chrome pump back in the day.
The springs on the diaphragm’s get weak and the pressure would drop drastically .
That’s something to consider .

Tommy
 
RustyRatRod said:
That's reasonable. I would also replace ALL of the rubber hose in the fuel system with Gates Barricade EFI hose. Make SURE it doesn't just say Barricade. It has to say "EFI" on it to be the hose I am talking about. It's TOUGH and it's ethanol resistant. Remember, ALL means ALL, including from the tank sender to the hard line. I had that very piece on my truck soften up and was sucking closed on hard acceleration blocking fuel flow.
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Ok thanks that answered my question about why hardline is better and what to use where hardline is not practical.
I’ll look for that Gates Barricade EFI hose. Is it 5/16”? I forgot since I have 3/8 and 5/26 fuel line reels here.
 
340inabbody said:
Ok thanks that answered my question about why hardline is better and what to use where hardline is not practical.
I’ll look for that Gates Barricade EFI hose. Is it 5/16”? I forgot since I have 3/8 and 5/26 fuel line reels here.
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Original is 5/16. Double check though, as these girls are old now and stuff like that gets changed around.
 
Meh, says minimum is. 2.0 psi, this is a Carter pump listed for a 1970 318 and 340

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oldkimmer said:
I to

I totally agree. I had to drain the liquid out of mine. Kim
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It’s strange because a pressure gauge is about as simple as a mechanism to design and produce.
I did check my float bowls and the levels are tip top. That with the information above regarding minimum psi from the pump means I will put my new wix filter in and replace my lines with hard-lines and the efi hose.
 
Well this is my findings. On my race car with an Aeromotive 2000 pump my fuel pressure was 11 cold and 4 warm. Even though it was running fine I drained the gauge. Now sits at 8 psi. Kim
 
Liquid-filled fuel pressure gauges are known to be problematic like that. Not sure what ever drove the need to have them in the first place. If it was needle bouncing, it seems like a well-functioning pressure regulator solves that issue.

I have an Aeromotive pump with a Holley old-school regulator. I set my fuel pressure to just under 6 psi where it stays no matter the temp or driving demands, track or street. I use this 0-15 psi AutoMeter Sport-Comp gauge out on my cowl (bad pic quality taken through the windshield!):

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340inabbody said:
Sounds like there are few if any fuel pressure gauges worth buying for automotive applications…?
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I think the problem is ALL of them, no matter the type or cost are easily influenced by outside sources. Heat, cold, vibration and on and on. They are a gauge like any other, just meant to be an approximation.
 
I plan to check the gauge in the morning. Sounds like it’s more than possible ie probable when it gets warm it slumps 50-60% from what Ive read. Checking it right away will tell me for sure if thats the case. No sense throwing money at it if the whole thing is problematic…….

Will report back.

Just fixed my charging issue by bench testing my VR which wasn’t coming on/shorting at all. The new one trips at 14.5V …
 
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