Bad efi fuel pressure regulator, right?

[briancave]

I recently put '98 explorer efi /mustang harness on my 302. Runs awesome, way better than it ever did with a carb. Fuel rail doesn't hold pressure when off though. Normal fuel pressure with key on,engine off (40psi)and key on engine running (30psi). When turned off, fuel pressure drops immediately. I did some tests and if I pinch off the return fuel line right before I turn the fuel pumps off, it holds pressure fine. Am I right in thinking that this points to the fuel pressure regulator and rules out the fuel pump and injectors as the culprit. I'm bummed because I replaced the original with a new one just to avoid this type problem and threw the old one away. How big of a deal is this if the only problem seems to be not maintaining pressure when the engine is off?

 

[Viperwolf1]

It's not a big deal. Could lead to extended cranking but probably not leaking enough to cause a lean condition when running.

 

[ScanmanSteven]

As long as the fuel pump cycles on when you first turn the key on it isn't a problem. After 3 regulators I've decided it no big deal, it doesn't need pressure when it's off. As soon as I turn the key it builds and holds so I'll say not to worry.

 

[Mikey]

I have two EFI cars, a 89 GT and 86 Capri....this would be a bad check valve internal to the in-tank fuel pump, I believe.

 

[Broncobowsher]

I have two EFI cars, a 89 GT and 86 Capri....this would be a bad check valve internal to the in-tank fuel pump, I believe.

Not with the pinched return line confirmation. Bad check valve in the pump would bleed down just as fast even with the return line pinched.

Brian, you are correct. The regulator isn't sealing. Probably not a problem outside of a longer prime to start it. Nice to have it working right, but shouldn't be causing you any drivability issues. Fix it when you get around to it.

 

[briancave]

Thanks for the confirmation on my diagnosis. The funny thing is that it starts right up. There's not much cranking at all. Maybe if it had pressure in it, it would fire up just half a crank earlier, I guess I'll find out if and when I replace it.

 

[pcf_mark]

Not to high jack but I have similar question. I do not have my fuel pressures but I have a new regulator with less than 500 miles on it. I installed it as part of my EFI conversion. Truck runs awesome. But when I start it up I need to crank for 6-10 seconds before it catches. If I cycle the key three times which runs the fuel punp for a few seconds each time. Then it cranks only 2-4 seconds and starts right up.

I have a mid 80s Ford truck EFI pump and filter on the rail to the stock rail connection and then out of the rail back to the tank. Is there something I am missing that would prevent the fuel from draining back?

 

[Broncobowsher]

Not to high jack but I have similar question. I do not have my fuel pressures but I have a new regulator with less than 500 miles on it. I installed it as part of my EFI conversion. Truck runs awesome. But when I start it up I need to crank for 6-10 seconds before it catches. If I cycle the key three times which runs the fuel punp for a few seconds each time. Then it cranks only 2-4 seconds and starts right up.

I have a mid 80s Ford truck EFI pump and filter on the rail to the stock rail connection and then out of the rail back to the tank. Is there something I am missing that would prevent the fuel from draining back?

You need a pressure gauge and some vise grips to crimp off feed/return lines. After you correctly diagnose the problem then you can go chasing parts. Guessing what is wrong is a horrible way to try and fix things. Very expensive and very easy to turn a single problem into multiple problems.

 

[welndmn]

Not to high jack but I have similar question. I do not have my fuel pressures but I have a new regulator with less than 500 miles on it. I installed it as part of my EFI conversion. Truck runs awesome. But when I start it up I need to crank for 6-10 seconds before it catches. If I cycle the key three times which runs the fuel punp for a few seconds each time. Then it cranks only 2-4 seconds and starts right up.

I have a mid 80s Ford truck EFI pump and filter on the rail to the stock rail connection and then out of the rail back to the tank. Is there something I am missing that would prevent the fuel from draining back?

Get a simple gauge that's rail mounted off the schrader valve, they are 20-40$ .

I'll agree with everyone else too to the OP, the regulator is leaking.

 

[pcf_mark]

What prevents fuel drain back? Is there a check valve in the pump and/or one on the return line?

I'll get the gage but I would like to know if I missed something in the thousands of pages I read on EFI conversions.

 

[Broncobowsher]

What prevents fuel drain back? Is there a check valve in the pump and/or one on the return line?

I'll get the gage but I would like to know if I missed something in the thousands of pages I read on EFI conversions.

Depends on where it is draining. If the regulator bleeds (like the OP) that is where the pressure is going. There is suppose to be a check valve in the pump to keep it from draining back to the tank on that side. The test is to build pressure and clamp off the line and wait. If the pressure stays up the clamped off line is preventing drain back in whichever side is clamped off. There is another possibility, injectors can leak and bleed pressure there. You find that pretty much by process of elimination.

 

[anoblefox]

on the factory ford efi systems, there is a "duckbill valve" where the return line goes back to the gas tank. This is not necessarily designed to hold rail pressure, but it does keep the fuel in the RETURN line from draining to the tank after you shut the engine up. This is to reduce cranking time on startup.
If you look at the underside a 86-93 mustang in tank pump assembly it is a pencil eraser colored valve with a slit that opens up while the engine is running.
I do not know if this type of valve is used on the "returnless" system however.

 

[pcf_mark]

I have nylon line so I cant crimp it as a test. I'll see the pressure on shut down and then 24 hours later to see where I'm at. I could take off the quick disconnect on one side then the other.

 

[Broncobowsher]

I have nylon line so I cant crimp it as a test. I'll see the pressure on shut down and then 24 hours later to see where I'm at. I could take off the quick disconnect on one side then the other.

You have quick connects? Get some junkyard fitting and make rubber sections that can plug inline to the quick connects. Now you can pinch them off.

 

[Mikey]

I think I'd install a valve rather than rubber...with all the alcohol in the gas these days...

Then, you would have another anti-theft device....