Turn off key, fuel drops to ZERO psi instantly. HELP!

[gcomfx.com]

My car has had an ongoing idling/starting problem. I've done so many things in the last year to fix it, I've forgot most of them. I changed my 190 pump for a 255 - didn't help. Thought I found a blown intake gasket. Fixed it. No change. Changed TPS, IAC, plugs, wires, coil, rotor, etc. I've had the car hooked up to a drivability dyno... didn't find anything. Even ran that smoke machine that checks for vaccum leaks. I had a code once that showed a 511 - swapped computers in the car. No change. Notice stock replacement balancer was a "little" off, put a nice pioneer on it. No change to idle.

Compression check is low, but for 185,000 miles and 4 years of juice not too bad. All cylinders were in the 110-115 psi range.

Last w/e I changed to a kirban regulator and rail mount guage. Didn't help. Although I discovered something I think is odd. My car does not hold ANY fuel pressure when I turn off the car. To cure the starting, I can turn on the key, pump kicks in and primes the system, try to start it, it won't most of the time. If I prime the pump twice it will fire right up.

Could it be as simple as my gas cap? It's cheap, so I'm going to try it.... but is there anything else I can try? It's like the fuel is going somewhere besides the rail. My car used to squirt ya, when you relieved pressure at the shrader valve. When I put the guage on, I tried to relieve the pressure first, and there was NONE.

 

[95cobraguy]

sounds like the pump is acting up again.

 

[BlackVert]

is there a one-way valve somewhere?

 

[gcomfx.com]

is there a one-way valve somewhere?

I don't know much about the fuel system.

 

[gcomfx.com]

sounds like the pump is acting up again.

Seriously? You think two in a row?

 

[SorsCode]

don't have an injector stuck open do you?

 

[HISSIN50]

There is a check valve in the pump to keep fuel from backflowing. The regulator can pass fuel and the injectors can dump fuel.

You can carefully crimp (with fuel line crimpers) the return line right as you shut it off. Note if the pressure remains high. If so, the reg is passing gas back to the tank. If the pressure still drops instantly, the check valve is where I would look.

Those are the big players that can cause an instant loss of pressure.

Some aftermarket FPR's will bleed pressure off pretty quick after shutting down. This is not necessarily bad as there is no need to have the system pressurized when the car is off. But it shouldnt be instant, nor should you have to multi-prime the car.

The gas tank is vented to the charcoal cannister, and the gas cap itself has a relief. I would not be lookin there for an issue. MHO.

Good luck.

 

[gcomfx.com]

I have had to change the charcoal cannister in the past. It was spewing raw fumes in to the engine bay. :?

 

[gcomfx.com]

don't have an injector stuck open do you?

Not sure.... My car was running lean on the juice last time I dynoed it. I'm thinking if I keep the dry shot I should bump up to 30lbers (New M/A as well). I'm trying to save money for a new engine set up. (Nothing crazy, just 306 with good heads) and would rather not just keep throwing money at this.

 

[RIO5.0]

Fuel pump would be the first guess for me to...I had the same thing...The Walbro fixxed that and I have a Kirban to, my gage holds pressure for at least 1/2 hour after I shut it off now and the pumps 2 yrs old...
I would try what Hissin mentioned to see what that shows. You can buy those rubber brake line clamps pretty cheap...
With everything you did thats wack...Mine bled instantly to 0 with my old pump and the Kirban being fairly new, so my thinking would be thats ok??
I wouldn't think the injectors wouldn't be able to bleed off pressure that quickly and have never heard that being an issue in pressure loss...

 

[95conv5.0]

the only thing that holds presure when the key is turned off is the afpr,

 

[HISSIN50]

the only thing that holds presure when the key is turned off is the afpr,

and the aforementioned Check valve on the pump-side.

 

[gcomfx.com]

Man it's just hard to believe a brand new pump would act like an older one and have the same exact problem.

When you say check valve do you mean that little rubber nipple looking thing held on by a hose clamp? If so is that a Ford only item? It might be the cheapest thing if the clamp works out. Or am I looking at a whole new assembly in the tank to change the check valve? Guess I'm not sure what it is.

While this whole thing does suck, I do feel like I'm at least FINDING something now. I've spent a year chasing a gremlin that many different people haven't found.

 

[HISSIN50]

IIRC, there should be a little ball in the outlet orifice. WHen fuel pushes on it (positive pressure from fuel flowing out of the pump), it allows fuel to flow. But when there is no positive pressure, the ball simply falls back (gravity) and closes off the orifice. This is what gives you resting pressure.

 

[gcomfx.com]

So I may have a bad ball?

Guess I'm still wondering what to do if the test of the return hose clamp still holds pressure. Am I looking at buying a whole new assembly for the tank and just swapping my new pump into it? If so, that sucks, but it's not like I'm new to dropping the tank.

 

[HISSIN50]

So I may have a bad ball?

Guess I'm still wondering what to do if the test of the return hose clamp still holds pressure. Am I looking at buying a whole new assembly for the tank

If it holds pressure with the return line crimped (but loses pressure if the return line is not crimped) that suggests the pump is ok.

 

[gcomfx.com]

Where would you suggest I crimp it at? Back by the tank or closer to the regulator? I'm not sure where all the rubber hose connections are that are easy to get to.

Oh and THANK YOU for your help. I really appreciate it. I would love to get this sorted out before any of our big club events. Ideling is kind of important with an AODE car.

 

[HISSIN50]

I would crimp the line up by the FPR. It is easy to access (one person crimps while the other shuts the car off at the same time) and it is closer to the FPR, which is better for test validity.

Good luck.

 

[gcomfx.com]

Guess if it works I could test it back by the tank a second time and see if there are any leaks in the lines.

Oh, and the CEL light came on this evening for the first time in a LONG time. Always in the past it meant I was running to rich when I cranked up the Fuel Pressure for the juice. I'm interested to see what the computer stored. It did go out after a minute or so, and never came back on. However the car did die while sitting in the drive thru line waiting for food. It was in Neutral too under no load by the tranny.

Whatever the problem is, it's getting worse... so maybe it'll be easier to find.

 

[Zero Signal]

I'm on my second FPR and I think my 3rd fuel pump so far so a bad pump wouldn't suprise me. Just pinch the return line near the fender in the engine bay to check the pump. There's no easy way to eliminate a bad injector though.