Fuel pressure gauge

[gtlotus]

I have a 1800 w/dual IDF 40. Electric fuel pump, pressure regulator and gauge. The problem I’m having is the fuel pressure; it will go from 4lbs to 0 lbs. I’ve tried different pumps, regulators and gauges. I have adjusted the floats.
This is with the engine running. Nothing changes. It stays the same. Sometimes it’s around 2 to 3 lbs and the next time I look at the gauge it’s 0. The engine is still running.
I feel that I have a fuel pressure problem because when the pressure is at or around 2 to 3 pounds the car runs it’s best. I must be missing something.
Thanks in advance for your help.
Gene

[blazingspider]

Where is your fuel pump located? It should be in the trunk and mounted on the rear bulkhead as low as you can get it.

How old is your fuel filter. Could it be plugged up a bit?

Have you pulled the fuel sending unit and checked the sock at the end of the pickup tube? What does the inside of the fuel tank look like? Is there a lot of rust?

Have you checked all of your fuel lines, starting from the trunk and working forward? Old rubber fuel hoses can get porous and suck air.

[gtlotus]

Thanks for the reply. The pump is new and in the trunk and mounted on the rear bulkhead as low as I can get it. All the rubber lines are new. The pickup in the tank is new. The filter is new. ??????????????
None of this makes any sense. Any more ideas?

Thanks

[blazingspider]

There are 2 rubber fuel lines under the car that connect the hard fuel lines together for the supply and return runs. Did you replace those?

You may want to review this video about installing idfs on a spider. These guys know what they're doing and maybe you can spot something in your setup that may be giving you a problem.

https://www.youtube.com/watch?v=7P5aHGX ... 4sLbbUB4LS

Good luck

[blazingspider]

One other thought; is you gas tank venting correctly? Loosen the gas cap and see if that makes any difference.

[gtlotus]

Thanks again for your replies. I made sure the tank is vented. I replaced all the rubber lines. I'm not using a return. I watched the videos. Thanks.
What I started to do is remove the fuel line from the front carb and place a valve in line, so I can see if the pressure holds with the carbs out of the circuit. If that holds pressure then it must be something wrong with the floats. Or that is the direction I will be headed.

Thanks again for your help.

Gene

[aj81spider]

A question and another thought.

Question: If you don't have a return to the tank where is your pressure regulator dumping the excess fuel?

Thought: If pressure is dropping to zero and that's the cause of your problem that means that not enough fuel is being supplied to keep the pressure up. That can only happen if the pump can't supply enough fuel (you said you tried several pumps, so this seems less likely) or if the lines are not big enough to provide enough fuel. You replaced the rubber lines, but is it possible there is a clog in the metal lines (or they are pinched somewhere? Have you tried running the pump with the line going into a bucket to see if you are getting reasonable flow?

[gtlotus]

Update. Yesterday a friend and I tried a number of things. First we replaced the 3.5psi / 28gpm pump with a 9psi/90 gpm pump. No real change. Then we replaced the regulator with a new one (different style) > no real change. Then we used the 9psi/90gal pump, with the new regulator and feed the pump from a gas can. Things got better but, not right. The regulator was set at 3.5 lbs, but the gauge only reach 2psi (yes the gauge is good) no matter if the regulator was set above that. But the good news is the pressure held steady at 2psi. So, next we hooked the 3.5psi/28gpm pump back up and ran a 5/16 fuel line outside the car. This time the pressure held at 2psi no matter if the regulator was set above that. It appears that there isn’t enough volume. The car idles fine at the 2psi but, I’m concerned that under a load it will be too lean.
Thanks again for every ones help. Any more ideas?
Thanks,
Gene

[gtlotus]

Yesterday I replaced the fuel line from the tank to the pressure regulator (5/16). Now all components including the fuel pickup in the tank, fuel line, regulator, gauge and the needle and seats in the carbs are new. When I started the car the fuel pressure showed 3.5 psi, just what the regulator was set at. The car ran fine and I let it Idle for 15 or so minutes. Still 3.5psi. I drove it to the store and back and it runs great. When I got back I checked the gauge and it read 0psi, but it runs great. It appears there is not enough volume to hold the pressure, but I can’t figure out why.
Does anyone have any more ideas?
Thanks,
Gene

[gtlotus]

I'm going to try a return line. What size re-stricter should I use?

Thanks,
Gene

[fiatfactory]

.

[gtlotus]

Sorry I wasn't clean on my original post. I'll give it a try.
Thanks,
Gene

[gtlotus]

Where should I place the T piece ? Between the pressure regulator and the carbs or before the regulator? Or maybe the re-stricter should be after the carbs?
I just what to make sure that I'm doing it right.

Thanks,
Gene

[Jon124]

Rather than using a t fitting you can also get fuel filters with a built in return line, example fram G3499. Not sure if this would work for your application, but something to look into.

[gtlotus]

UPDATE I installed a return line. It now hold 2.5 psi all the time. I don't really understand why the return line is needed, but it works. Thanks for everyone's help.