Fuel pressure mystery

I have a 92 Ford ranger with the 3.0 and I have a mysterious fuel problem. The truck run and drives great, I try to stay on top of any problems. But it loses fuel pressure after I turn it off, and when I say it loses pressure I mean my lines are bone dry in the morning. I have to turn key and let the fuel pump build pressure before I start, that takes about 4 minutes in the morning. After a few minutes I hear the pump turn off at starts like a champ.
So far I replaced the fuel pump twice, the fuel pressure regulator twice, fuel filter, and the vacuum lines to the regulator since they were bad. I have tested my injectors with a meter, checked the o-rings and the little plastic peice on the tips. I also pulled the rail with the injectors to see if they leaked. I inspected all the lines looking for a leak and found nothing.
Now the crazy thing is if the weather is below 50°F it maintains pressure, so I have no problems in the winter. It got cold and I thought the problem fixed it self but then it warmed up and now I am stumped.

So someone please give me some ideas. I really don’t want to replace all the injectors and fuel lines.

One thing that’s certain, it has to be going somewhere. I’m presuming you see no signs of external leaks or smell gasoline. Seems like you’ve already covered the three most likely culprits, the pump check valve, fuel pressure regulator, and leaky injectors. Is there a path from the fuel rail to the charcoal canister? If so, check that. The only other thing I can think of is there’s usually a way built into the fuel rail or manifold to relieve the fuel pressure for testing purposes. Maybe that part is defective.

Hmm didn’t think about that, I will look into it this Sunday

Another idea, there’s usually a pressure release valve incorporated into the pump that generally never operates unless there’s a clog in the fuel lines somewhere, usually that would be a clogged fuel filter. Perhaps your fuel filter is somewhat clogged, and allowing that pressure release valve to open.

Otherwise I’m thinking this could be a story line for another episode of Dr. Who:slight_smile:

I’m cannot think of any diagnostic input beyond what’s already been written, but until you get the problem solved you could simply turn the key to ON a few times for 3-4 seconds each morning before turning it to START. That would allow the lines to refill/pressurize and make starting the vehicle easier.

Just a thought.

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If you are OK at 50F or less but have a problem above that temperature it must be a very fine leak associated with expansion or contraction of (probably) a metal part. Do you have an air-bypass that might be leaking and allowing gravity to empty the lines (but only when it is warm enough to cause something to expand)?

Turning key on a couple of times doesn’t do much, I have to leave the key on and wait for the fuel pump to turn off.

As far as I know I don’t have an air bypass.

I have found that problem to be caused by the ECM failing to initiate the fuel pump to prime the fuel rail. The ECM grounds the fuel pump relay to turn it on. Check the fuel pump relay and if a light blue with orange strip is connected to either pin # 85 or 86 connect a test light to that wire at the relay and with the key on ground the test light and listen for the fuel pump to turn on. If it does the next time you expect that the engine won’t start connect the test light and if the engine immediately starts you’ve found the problem.

I found the details re the wire color and relay from scribbled notes in the margin of an old shop manual and feel sure it was correct for the Ford truck that I was dealing with and it was noted the same for a Ranger, Econoline and Aerostar. I recall that was a somewhat common problem long ago.

And there is an air bypass solenoid.