loosing fuel pressure

Whats up guys ive got a 92 B2600i and over night my truck will loose fuel pressure and take awhile to start in the morning any ideas or suggestions thanks

There is a check valve at the end of the fuel pump that is suppose to prevent it from returning the fuel back from the same line.... Also check your o-ring and fittings for a leak along your fuel rail and fuel pressure regulator.

Is the check valve in the tank

The check valve is built into the pump, so yes it's in the tank. If it's bad, I think you'll need to replace the pump as this is what Mazda prescribes if you're loosing pressure on the backend.

As Berryserious mentioned, you need to check the system to find out where it's leaking down from. Look for the obvious signs of leakage around the filter, dampener, fuel rail, injectors, and then the pressure regulator. You might want to try jumping the yellow connecter under the hood to to pressurize the system while looking around. Jumper the yellow connecter and then turn the key on and this will power the pump until either the key is turned off or the jumper is removed.

The first pressure check would be to confirm that pressure is in fact bleeding down. If so, then you'll check it again to see it it's the pump or somewhere between the pump and filter. If not, then it's one of the things mentioned above. Give me a few and I'll post some of the procedure to check these. These will be from a 91 manual, but there shouldn't be an significant differences.

Before you get started, if you are not familiar with depressurizing the system, you can do it by starting the truck, and then pulling the Fuel Pump relay (aka "circuit opening relay") located behind the driver's side kick panel. It will take several seconds to die. Here are the steps for releasing and re-priming fuel pressure along with a pic of it's location:







Here is the basic pressure drop test....





Here is Pump Pressure Drop





Pressure Regulator:

By the way, if you pull the vacuum line off the regulator and find fuel, then it's bad - needs to be replaced.



Regulator Replacement:





Injectors

If you end up going this far and pull the injectors, it would be a good idea to replace the o-rings and seals if they haven't been done in a while or ever. Might also be a good idea to send the injectors out for cleaning and they will come back with new seals, o-rings, grommets.

wow thats alot to check lol thanks man i will start checking things tom and keep u informed on my progress

without diagnosing anything or seeing or checking anything on your truck .... The check valve in fuel pump has been the culprit on my truck when i had a similar problem...... Good luck

How much does it appear to loose (how slow starting) after sitting 10 min, 1hr, and 3 or 4 hours?

Until you get it resolved, you can cycle the key to the ON position for a couple of seconds, then off, and repeat 2,3, or 4 times as necessary to build up the pressure before you start it if you want to save some wear on your starter. I don't remember the spec, but I think the pump runs about 2 or 3 seconds when the key is turned on before turning off if the ecm doesn't sense the engine is running - or at least turning.

I can get it started in the morning and drive it to work which is 15 mins then it sits for 8 1/2 hrs then when i leave for work it starts right up its just if the truck sits overnight i usually get home at nights bout 11 and get out the door to crank it at 6 and thats when it gives me problems also i do have a fuel cell its got the factory fuel pump and its mounted at the rear of the bed could i put an inline fuel pump on?? Also its about 25 degrees normally in the morning

It sounds like it's a function of cold temperature (and time) more than just time alone since it can sit 8 &1/2 hours at work with no problems, but 7 hours overnight and then it's hard to start. It may be the fuel pressure bleeding down as you described. Or it could be cold natured or something else. How was it during the summer or warmer months when sitting overnight?

Before you open the fuel system up to start checking it, here is a real simple to test to confirm that it is the fuel pressure bleeding down. When you get ready to leave in the morning (and the truck is cold soaked), before you start it, jumper the yellow fuel pump test connecter and then turn the key on for 10 seconds to prime the system as described on the first page. If it starts right up, then you have reasonably confirmed that fuel pressure bleed down is causing the problem. If priming it doesn't help it start quicker, then you might have something else going on.

If it holds pressure good all day, but looses it in the cold overnight, I'm doubtful that the test procedures I posted earlier will identify much.

Your fuel cell is in addition to the factory tank? Can you describe your setup a little more. It would be nice to isolate the problem before you add a check valve into the system; but since it seems to be so slow and cold natured, it might be difficult.

Here is a shot of the yellow test connecter in case you're unfamiliar....