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Old 02-01-2016, 02:10 PM   #1
rfball
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Fuel pump or pressure regulator? or aomething else?

I'm new to this so please bear with me.
I have a 1995 Buick road master that doesn't like to start after it sits a few hours.
I have put a fuel pressure gage on the rail, and, with the key off, 0psi. When I turn the key to run, the pressure goes up to about 5psi then bleeds off quickly. cycling the key from off to run seems to consistently give the same results. Watching the pressure gage, if I hit start when the pressure is 5psi, the car will start, and the pressure will rise to 35psi. If I remove the vacuum line from the pressure regulator, the pressure will increase to 45-48psi. I can turn the car off, and restart with no problem at this point, as long as I don't wait too long.

My theory.
Either the fuel pump or regulator are letting the fuel bleed off over time, and somehow allowing air in the lines.

My question
How do I tell which is leaking? or am I way of track?
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Old 02-01-2016, 06:45 PM   #2
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Re: Fuel pump or pressure regulator? or aomething else?

Any raw fuel in the hose to the regulator?
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Old 02-01-2016, 08:58 PM   #3
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Re: Fuel pump or pressure regulator? or aomething else?

I am thinking fuel pump, check valve in the pump, or leak in the pump........

Do you have plastic lines between the rail and the fuel lines?

Or do you have rubber hoses?

If plastic lines, you need special valves to attach to the plastic lines(supply and return).....YOU CAN'T CLAMP PLASTIC LINES!

If you have rubber hoses, you need vice grip clamping pliers for hoses(rounded jaws).....otherwise rap a rag around the hose before applying regular vice grips....


first clamp the return line......cycling the key several times to on(don't crank) to see if pressure builds up.....if it doesn't, leave the return clamped....now have someone cycle the key to on several times, and when pressure starts to build, clamp the supply line......if pressure, whatever amount, stays, then the problem is in the supply line...if no external leaks in supply line, the problem is in the tank(pump or connection from pump)....

If pressure still drops after clamping the supply line, and no fuel comes out of the vac port of the regulator, then you have a leaking injector.....

I am assuming this is a V-8 with 8 injectors(Opti-Spark) rather than throttle body injection(only 2 injectors)
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Old 02-02-2016, 09:02 AM   #4
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Re: Fuel pump or pressure regulator? or aomething else?

Nope. the Vacuum line is dry.
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Old 02-02-2016, 09:09 AM   #5
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Re: Fuel pump or pressure regulator? or aomething else?

Thanks Tech II. Yes, it is a V8 (LT1) with 8 injectors, and it has rubber lines. I Hadn't thought of an injector leak. I assume you have seen that before. I will try your suggestion when I get off work, and let you know the outcome.
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Old 02-18-2016, 12:56 PM   #6
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Re: Fuel pump or pressure regulator? or aomething else?

Been a while since I posted this because I fixed the problem, and then posting seems to drop down on the priority list.
But since I hate to read a post that looks like it could help, and the solution is never posted, I don't want to be that guy!


When I removed the fuel pump, I found a rubber grommet that connects the fuel pump to the plastic hose that exits the tank. That grommet did not seem to have a tight seal, so I replaced that connection and the plastic line with regular fuel hose and hose clamps.

I did replace the fuel pump, because
1. it was under warranty and didn't cost me anything. (the pump also came with the fuel hose that I referred to above.)
2. once you have gone to all the trouble of pulling the pump, you don't want to do have to do it again because you guessed wrong!

With all that said, when I put it back together, and turned the key on, the fuel pressure increased and held! The car stated right up and has been running fine ever since.

Except for an oil leak that I discovered on the axle seal! but that is another story!

Thanks to everyone that gave input! It is appreciated!
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Old 02-18-2016, 01:42 PM   #7
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Re: Fuel pump or pressure regulator? or aomething else?

And like you said, it's good to know the fix to a problem, and only the original poster can do that.....
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