Weird fuel tank pressure problem!

[HaZmatt]

Ok guys im having a fuel issue with my 75 280z. I switched from EFI to carbs and had it running great until I switched to a different fuel pump and regulator.

 

I was previously running an Rx7 4psi electric pump. I switched it out for an Airtex 5-6psi pump because I could only get about 3 psi from the RX7 pump.

 

I also switched out regulators but that should'nt be the issue because they are plumbed the same.

 

Heres the issue:

 

When I installed the pump and turned it on it was vibrating like crazy and my pressure gauge was flickering at 0 psi.

 

Since then if I remove a hose anywhere from the tank, gas pours out heavily. Even out of the return line.

 

Heres what I've tried so far.

 

Bypassed fuel filter - nothing

 

Removed gas cap - nothing

 

Tried draining fuel from return line out of tank - just kept pouring out

 

Capped off return line at tank, hooked up pump and ran fuel through entire system with return line draining into bucket - 

Pump seemed to work fine, no clogs anywhere.

 

So i've come to the conclusion that the pump is fine, its just fighting the fuel coming back from the return. Causing the

0 psi and vibrating. 

 

Any ideas? I thought of just draining the tank and starting over?

 

BTW my evap tank is still hooked up normally just the line where the canister was in the engine bay is capped off. It ran fine like this for a couple months so I dont think thats the issue.

 

Any help would be greatly appreciated! Thanks

Edited May 30, 2015 by HaZmatt

[Patcon]

Was there a problem running at 3 psi? I don't totally understand how your fuel is plumbed. I would start with the old fuel pump if that's easy. See what you get. Replace the regulator and see what you get. If it showed pressure before with the old setup then one of the items you changed broke it. Does it run at 0 psi?

[HaZmatt]

Yeah it ran fine at 3 psi but at higher RPM it would cut out. Ive read that 4psi is recommended.

 

My fuel system goes like this: Tank-pump-filter-carbs-pressure gauge-regulator-tank

[HaZmatt]

The regulator may be bad. I'm troubleshooting now

[Zed Head]

It's not really clear that fuel isn't flowing and the carbs aren't getting fuel.  You said that fuel flows from the return line, but not clear if you meant from the tank or from the line after passing through the system.

 

In other words, summarizing, it looks like you're saying that you have a gauge that reads zero and a pump that shakes like crazy.  But the rest is kind of foggy.  Fighting fuel from the return doesn't make sense either.  Can't figure it out.

 

Is the regulator adjustable?  Could you have the lines backward at the regulator?  If you plumb the inlet line from the pump to the return port on a regulator, the pump will not push any fuel.  It can't push backward through the regulator.

[Pop's Z]

Haz, experience has taught me that a filter between tank and pump prevents crapola from messing up the pump. I don't think this is your problem, but it can't hurt. Did you do a tank cleanout?

 

Cheers, Mike

[Zed Head]

Forgot to say, at first glance the way a regulator works is kind of counter-intuitive.  The fuel doesn't push the valve open from the small port in the middle, it fills the volume under the the diaphragm and pushes it up, lifting the valve open and letting the fuel out the center port.  Make sure you have your ports right.

[HaZmatt]

I bypassed the regulator and it works fine now. Must be bad. Thanks guys

[Patcon]

Very good. Like Zed said verify the ports not all of them plumb the same way.

[HaZmatt]

Silly me. The regulator I bought wasnt a return style that I needed. That was the problem. 

[Patcon]

Very good. Glad you figured it out.