Fuel Pressure...Not making sense (Lars?)
11-13-2001, 04:16 PM
#1
Drifting
Thread Starter
Fuel Pressure...Not making sense (Lars?)
I have a fuel pressure gauge on the end of my Lars custom fuel line (at the filter in the dual-feed jobber). When I start the car, it comes up at about 3 psi at idle. With revving it will climb as the mechanical pump is working harder. This is a brand new '73 style pump (with the diverter on the pump and not the filter).
After a bit of driving, the pressure reading will be down, and often times it will just bottom out on 0 psi...yet the car continues to run fine. It will perk up with a rev of the engine, but will settle back on 0.
I originally thought that maybe the vented cap wasn't doing it's job, so when I saw the pressure sitting at 0 the other day, I took the cap off and left the tank open. No change...so, I'm guessing the cap is venting like it should.
The other interesting thing? It sounds like a waterfall in my gas tank...is the fuel (on a system with a return line) supposed to recirculate constantly? I know that it will ultimately keep the gas cooler and prevent vapor lock, but I never knew that it would make a noticible flowing sound.
So, I guess my two questions...what could be causing my lack of fuel pressure at the carburetor inlets? And, is that waterfall sound normal? :seeya
After a bit of driving, the pressure reading will be down, and often times it will just bottom out on 0 psi...yet the car continues to run fine. It will perk up with a rev of the engine, but will settle back on 0.
I originally thought that maybe the vented cap wasn't doing it's job, so when I saw the pressure sitting at 0 the other day, I took the cap off and left the tank open. No change...so, I'm guessing the cap is venting like it should.
The other interesting thing? It sounds like a waterfall in my gas tank...is the fuel (on a system with a return line) supposed to recirculate constantly? I know that it will ultimately keep the gas cooler and prevent vapor lock, but I never knew that it would make a noticible flowing sound.
So, I guess my two questions...what could be causing my lack of fuel pressure at the carburetor inlets? And, is that waterfall sound normal? :seeya
11-13-2001, 04:18 PM
#2
Drifting
Thread Starter
Re: Fuel Pressure...Not making sense (rainman69)
Oops, forgot: Could the pressure gauge just be bad if it reads for a while and then just reads zero? It's a mechanical pressure gauge. :smash:
11-13-2001, 05:08 PM
#3
Melting Slicks
Member Since: Oct 2000
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Re: Fuel Pressure...Not making sense (rainman69)
I'm not really much of an expert on fuel delivery here, but in our remediation systems we use a lot of mechanical gauges. Some are definitely more accurate and longer lasting than others. It's been my experience that even though a gauge has an operating range, it will be more accurate in the middle of that range, no in the extreme low or high range.
Also, looks like you have adequate fuel flow to carb but no pressure. but you also have a good flow back to the tank. Remember that flow and pressure are inversely proportionate. Because you have good flow both back to the tank, I would guess your pressure is going to be low, probably too low for the gauge to accurately read.
I could be F.O.S., but that's my theory :D
Also, looks like you have adequate fuel flow to carb but no pressure. but you also have a good flow back to the tank. Remember that flow and pressure are inversely proportionate. Because you have good flow both back to the tank, I would guess your pressure is going to be low, probably too low for the gauge to accurately read.
I could be F.O.S., but that's my theory :D