Inside Fuel Accumulator

[Bitsyncmaster]

Here is a photo of the parts inside the fuel accumulator. A massive spring. I was expecting a better bellows, can't see how these little rubber cups accumulate much fuel. There is a little "check valve" but there is a very small cut in the metal plate so it would leak a little. My guess is it's there to stop those little parts of rubber fragments from getting into the fuel system. It looks like the "bellows" are made with a cloth and then rubber coated on each side. The edges are missing that rubber coating probably caused by the ethanol fuel. This accumulator is 20 years old and was supplied by Hervy so not sure if it was NOS at the time.

[JohnZ]

Compared to the housing, the spring is HUGE!

[painterdave72]

I cut one open that failed a couple of years ago and yes the spring is huge.. on the one i cut open the check valve had somehow broken off of the one end and that is why it didnt work anymore...

[jackb]

Here is a photo of the parts inside the fuel accumulator. A massive spring. I was expecting a better bellows, can't see how these little rubber cups accumulate much fuel. There is a little "check valve" but there is a very small cut in the metal plate so it would leak a little. My guess is it's there to stop those little parts of rubber fragments from getting into the fuel system. It looks like the "bellows" are made with a cloth and then rubber coated on each side. The edges are missing that rubber coating probably caused by the ethanol fuel. This accumulator is 20 years old and was supplied by Hervy so not sure if it was NOS at the time.

Looks like an original. Compare to my old original accumulator:
https://dmctalk.org/showthread.php?16835-Hot-start-issues-do-these-details-sound-like-my-accumulator-is-bad&p=239249&viewfull=1#post239249

[Bitsyncmaster]

What I have learned from all my rest pressure testing:

The fuel accumulator takes 40 seconds of pump running to fully charge the accumulator.

The accumulator sets the start rest pressure about 43 to 41 PSI. That is the fully charged accumulator spring value on the inside "bellows".

The accumulator has emptied around 30 PSI. Pressure falls of rapidly below that value because the accumulator is not providing any more fuel.

Primary pressure values do change if engine is running or not. Depending on your battery condition that change could be 5 PSI. Just a design fault of our PPR that changes with the amount of fuel flow due to higher voltage at the fuel pump.

Don't know why they made our accumulator with one fuel connection with a larger size. They both dump into the same air space in the accumulator. There are other accumulators with the same performance and only difference is both fuel connections are the same size.

Now my car shows 2.5 hours of rest pressure time (drop to 10 PSI) when engine is cold. That time goes to 1 hour and 50 minuets when hot. Not sure if that is normal or just a problem with my fuel distributor.

I'm also now using a different check valve at the fuel pump. No change in rest pressure time but this new one has a steel ball seat without any o-rings. It's a Delphi FA10016-11B1 BFA10016 part numbers on the box. Just in case the standard one is out of stock.

I'm also using a softer PPR o-ring, again no rest pressure time changed.

I have been able to get longer rest pressure times with the mixture screw set more CCW than normal. Probably just my fuel accumulator tolerance on that plunger.

[Bitsyncmaster]

Here is a photo of the parts inside the fuel accumulator. A massive spring. I was expecting a better bellows, can't see how these little rubber cups accumulate much fuel. There is a little "check valve" but there is a very small cut in the metal plate so it would leak a little. My guess is it's there to stop those little parts of rubber fragments from getting into the fuel system. It looks like the "bellows" are made with a cloth and then rubber coated on each side. The edges are missing that rubber coating probably caused by the ethanol fuel. This accumulator is 20 years old and was supplied by Hervy so not sure if it was NOS at the time.

I figured out why they have that check valve. What it does is provide all the fuel in the accumulator quickly for an engine start. It also probably helps with reducing the pulsing of the fuel pump when running. The small orifice (cut under the check valve) that makes the full charge take 40 seconds is there to let you run the engine even if the accumulator has failed (leaking fuel to the return line) and give you full pump pressure when the accumulator is still charging.

[David T]

I figured out why they have that check valve. What it does is provide all the fuel in the accumulator quickly for an engine start. It also probably helps with reducing the pulsing of the fuel pump when running. The small orifice (cut under the check valve) that makes the full charge take 40 seconds is there to let you run the engine even if the accumulator has failed (leaking fuel to the return line) and give you full pump pressure when the accumulator is still charging.

The accumulator does 2 things. It smooths out the pulses of the fuel pump and it provides enough pressure to operate the fuel injectors till the fuel pump can build up full pressure when the motor is too warm to make the Cold Start Valve operate.

[Emit]

I'm curious how a more modern EFI car deals with the aforementioned issues without an accumulator, like holding pressure, pulsing etc.?

I put EFI in a carb car and it seemed to me that the fuel regulator did the hard work, something like this: https://www.summitracing.com/parts/tnk-afpr1

If there is a modern fuel pump installed and you can set the regulator for your pressure of choice does that not solve for the accumulator ? Genuinely curious :)

[Bitsyncmaster]

I'm curious how a more modern EFI car deals with the aforementioned issues without an accumulator, like holding pressure, pulsing etc.?

I put EFI in a carb car and it seemed to me that the fuel regulator did the hard work, something like this: https://www.summitracing.com/parts/tnk-afpr1

If there is a modern fuel pump installed and you can set the regulator for your pressure of choice does that not solve for the accumulator ? Genuinely curious :)

The rest pressure problem is mostly a problem with engines that have injectors that only open with pressure. Gas bubbles build up in the injector lines which compress and then the injector does not open. EFI injectors open electrically so it can purge any gas bubbles. Most fuel pressure regulators work the same as our regulator built into the fuel distributor. They use a spring valve to return fuel when pressure is to high.