fuel pressure accumulator

[johann86911]

Hi guys,

Apologies for the potentially dumb question.

How do you diagnose whether the above needs replacement?

I've got an SC. It's having a few warm start issues. I know the above is perhaps an easy replacement. But how do I know for sure whether that is in fact the problem?

The Bentley manual says conduct a Control pressure, residual pressure and system pressure test and then refers to "the line pressure regulator"? can One assume this means the fuel pressure accumulator?

[LakeCleElum]

Yes, bleeds fuel pressure when warm. Can also be the check valve in the fuel pump on certain years.

I had the same problem a year ago. Solved with a new accumulator from our host....

[johann86911]

righto! thanks. will see how I go!

[ossiblue]

I'm not familiar with the accumulator being referred to as the "line pressure regulator," though that may well be what Bentley is refering to. It does not bleed off pressure but instead evens out the pulsation of fuel delivery and provides a steady flow of fuel. The warm up regulator (WUR)/control pressure regulator has the job of bleeding off pressure/increasing pressure to the system.

As far as knowing if the accumulator is your problem, yes, you need to do the pressure tests to see if your system holds pressure after shut down, and then determine which component may be at fault. Assuming that's the case, to first check the accumulator, remove the line from the bottom of the accumulator, and plug the disconnected line so fuel does not come out. Put a container under the opened connection of the accumulator and start the fuel pump. If fuel comes out of the bottom, your accumulator is bad. If no fuel comes out, the loss of residual pressure is somewhere else, typically the fuel pump check valve, the WUR, or the fuel distributor pressure relief valve. All should be tested to determine which is at fault.

[boyt911sc]

You can test a fuel accumulator installed in the car or on a bench. If you have a fuel pressure gauge, check your residual fuel pressure. A very simple test is to pressurize the FA . If the membrane inside the FA is ruptured or broken, it would leak. Or simply test the FP with the return line from the bottom of the FA disconnected. Run the FP for 2 or 3 sec. (max). and a place container under the FA to collect any fuel that might come out from it. Have the disconnected return line go to the container too. If fuel flows out from the FA.......it means it has a rupture or broken membrane. Or if you want to do the dry method technique, simply pressurize the FA with air (5 psi.) and if has leak, it won't hold the pressure.

If you remove the FA from the car, you could fill the FA with gasoline or water. If it does not leak down, then the membrane is still good. Dry the FA well before putting it back if the FA is good. Otherwise, throw it into the dumpster.

Tony

[Tidybuoy]

May I add a little:

There is also a fuel pressure regulator that is built into the fuel distributor that also maintains "system pressure". This means that when the fuel pump is running, the system needs to have approximately 5 bar of pressure being put out by the fuel pump, and any excess is bled off back to the fuel tank.

This fuel pressure regulator in the fuel distributor is also one of the components that holds pressure after the car is shut off. There is a tiny o-ring on the tip that seals and if the o-ring is broken (as was the case in my car), the system will not hold pressure and will have difficult starts - both cold and hot.

[johann86911]

Thanks for all the information guys. This gives me bit more confidence on diagnosis.

[boyt911sc]

Johan,

Remove the fuel accumulator from the engine bay and perform this simple air-pressure test that would require a few seconds only. If you don't have an air compressor, simply blow air like blowing a balloon to inflate it.



Test A:
Place some water in the glass or container just high enough to reach the threaded section of the bottom port. Plug the outer port (top) using your thumb and blow air using your mouth. If the membrane is ruptured or broken, air bubbles would be coming out from the bottom port.

Test B:
Air dry the fuel accumulator and set it up as shown in the above picture. Slowly fill the the FA with liquid (gasoline) up to the rim without spilling the liquid. It is imperative that you don't over-fill the FA and closely observe any liquid (gasoline) dripping out from the bottom port.

Both these tests are reliable to confirm the condition of your FA and avoid guess work. If the test/s confirm it is bad replace it. If it passed the test/s, you know the culprit is some where else.

Tony