Why or when to replace the accumulator (SC)
 

SO I was browsing the classifieds and I have seen at least 3 different SCs that have had the accumulators replaced... is this a common problem> what is its function> I thought it held fuel for high need times ie acceleration..what is the symptom for RR on this?


Chirs

The symptom would be poor warm starting issues. The accumulator and the fuel pump check valve keep fuel pressures from rapidly decreasing on engine shutdown. This problem can be further identified by using the CIS fuel pressure gauge and reference information (Bentley manual, workshop manual, etc.) to target the symptoms, identify the problem and prescribe a cure.

Brian

Thanks, I am good there, just cold start is a problem for me.

Chris

My 80SC Targa's fuel accumulator is being replaced as I type. The car has 43k on the clock. Or at least that's what everything says (my mechanic thinks it's the original speedo).

Any idea why or when these things generally go bad? Also re-doing the wiring to the spark plugs. Yowser of the a bill, it's gonna be....

There are moving parts and rubber components inside the accumulator. It's like a bellows that balances out the inlet and return fuel line pressures (at least on an SC that's what it does with connections top and bottom). That said, I haven't replaced one yet (knocking on wood).

Brian

The accumulator is, in theory, a lifetime part, but, like fuel pumps, they do fail. Unfortunately there in no pattern to when it will happen. The symptom is when the car is shut off hot, and sits for between about 5 minutes and about a half hour, the car just cranks and cranks when a re-start is attempted. Fortunately, if the battery is strong, the car will eventually start...

Pete, have you ever opened one up? Does the rubber bladder inside get constantly exposed to fuel? Thanks!

Brian

The sectional views show that the diaphram is constantly in contact with gasoline. As the fuel pressure rises from zero, the spring that supports the diaphram compresses until it hits a mechanical stop. The fuel pressure continues to rise but the diaphram does not move further.

I'm guessing that the mechanical stop is reached at a fuel pressure of about 20 psi or so. When you shut down the engine, the pressure drops fairly quickly to about 20 psi then bleeds slowly down to zero over an hour or so. For a -74 and later CIS, the only bleed is in the WUR, so the rate of pressure drop should slow as the pressure itself drops.

My '80 SC's accumulator lasted 25 years/180,000 miles.

got more than 100K so far on my original. Thought I was having a hot start problem but apparently I am not. So - I would say, at least in my case, they last a long time - 26 years/100K miles

I played with the accumulator in my SC cabriolet last fall after I removed the engine. You can hit the top portion of the accumlator with an air hose nozzle (I think I was using 20 PSI or less, and you'll feel the bellows move). Remove the nozzle and the accumulator would slowly bleed off the pressure. Interesting device.

To clarify, the air pressurized accumulator will bleed down in a few seconds, not anything like how it functions in its closed-loop application. I was simply interested in seeing if mine leaked if I pressurized it with air.

Brian

I wish that I could answer yes, but of the many times that we had an old one on the bench, and a hacksaw at the ready, somehow we never quite managed to get one opened...

Fuel accumulator......
 

Brian,

For two-port FA, only the chamber side of the diaphragm comes in contact with fuel. But in three-port FA with drain line at the bottom side, both sides of the diaphragm come in contact with the fuel supply and return respectively.

The drain line (bottom) of the FA is connected to the return line in case the diaphragm ruptures. So both sides of the diaphragm is constantly exposed to fuel all the time.

Tony

Tony, do you figure the diaphragm is sealed to the outer accumulator case at the joint where the top and bottom sections meet (the part that's crimped over, kind of like how our gauge bezels are held on to the gauges)?

Brian