The fuel pressure on my Buick regal was only about 20 psi when the manual said I should have between 42 and 47. I replaced the fuel pump, discarded the fuel pulse dampener and put a hose there instead (this hose and instructions to use in place of the dampener came with the AC Delco fuel pump). Now when I run the fuel pump I get 45 psi (perfect!) but once the pump is turned off the pressure doesn’t hold and drops to about 20 psi (sometimes to 30, but that happens only about a quarter of the time). I replaced the fuel pressure regulator but the problem still persists. If I turn on the pump and then scrunch the fuel return line closed and then turn off the pump the fuel pressure will hold. If I do the same with the fuel supply line the pressure still falls off. Does anyone have an idea what could be going on? I am at a loss on this one.
Check to see if your Regal has an anti-flowback valve. Some are in the fuel filter. If it goes bad then the fuel system cannot hold pressure.
I don’t see a problem. When the fuel pump stops running, the pressure will bleed off, and that’s normal. And if you wait long enough the pressure will drop to zero. Again that’s normal.
When a fuel pump turns off it’s not supposed to maintain the fuel pressure. Instead it should prevent the fuel from draining back into the gas tank from the fuel system. With this fuel under zero pressure in the fuel system, as soon as the fuel pump runs again fuel pressure is immediately restored because you can’t compress a liquid.
This is some diagnostic information from ALLDATA…
Number(s) below refer to circled number(s) on the diagnostic chart.
Connect fuel pressure gage as shown in illustration. Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the gage. With ignition “ON” and fuel pump running, pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regulator assembly.
When the engine is idling, manifold pressure is low (high vacuum) and is applied to the pressure regulator diaphragm. Vacuum will offset spring pressure and result in lower fuel pressure. Fuel pressure at idle will vary somewhat depending on barometric pressure but, should be less than pressure noted in Step (1).
A system that does not hold pressure is caused by one of the following:
Leaking fuel pump check ball.
Leaking fuel pulse dampener.****
Leaking valve / seat within pressure regulator.
If you removed the dampener and didn’t install a new one, that is your problem. I have never seen instructions for a replacement GM fuel pump that called for removing the dampener. That dampener has a check valve that keeps residual pressure in the system, with out residual pressure you will have hard starting problems after the car sits for a short time.
This test a read says nothing about the pressure with the engine off. If the system held full pressure with the engine not running you wouldn’t hear the fuel pump spool up when you turn on the key.
True, it doesn’t mention what the pressure is supposed to do when the engine is off. The point was to show the OP that the dampener should not have been removed because it is suppose to maintain residual pressure in the fuel system.
Fuel pressure is suppose to hold for at least a minute or more, if it bleeds off then there is a leak in the system which needs to be addressed.
The fuel pump only runs for 2-3 seconds when the key is turned on, then it shuts down until the engine starts. The only reason it does this is to make sure there is pressure in the fuel system so the engine will start up. If the fuel system bleeds off all pressure then the 2-3 seconds that the fuel pump runs will not be enough to prime the system and the engine won’t start.
When this happens the most common complaint is the engines cranks excessively before it starts or have I have to try cranking the engine over a number of times before it starts.
All the OP said is that s/he followed instructions that came with the new fuel pump and that it was an AC Delco. It seems weird to me too, but maybe there is rhyme to that reason. Of course, it wouldn’t hurt for the OP to double check the part # to make sure the application is correct.
“If the fuel system bleeds off all pressure then the 2-3 seconds that the fuel pump runs will not be enough to prime the system and the engine won’t start.”
I’m not so sure that is accurate and assume it will vary. I know that my fuel pressure will zero out over night and I have no restart problems. I also know that it takes about 4 on/off cycles to get it up to pressure. I don’t have to do that to start it, however.
Most of the time there will be residual pressure on a fuel injected vehicle. If the fuel system zeroes out overnight then something is leaking somewhere. I almost always have to bleed off pressure on any fuel injected vehicle before performing a fuel pressure check. This is sometimes days after shutting off the engine. It’s rare if I find one that does not spray some fuel on the shop towel. I’ve only seen one vehicle with a fuel pressure gauge on the fuel rail and I think the residual pressure was about 15-20 psi.
Thanks everyone for your help. I appreciate it. I finally found the problem, I was loosing pressure at where the fuel return line hooks at the top of the gas tank. Now the pressure holds just fine. It was a super pain to find but eventually I lowered the tank a little bit and it held pressure so only when the line was at a certain angle did it let some out. I know I am no expert but on the comments about the fuel pressure dampener the description of the part it that it "reduces noise and vibration in the fuel line". Now I can hear the pump (of course my pump was faulty before but I haven't been able to hear it since I got the car). Also like I commented the fuel line and hose clamps to bypass the dampener came with the pump and I don't think that is an essential part.