elgy

It seems that my partially functional fuel accumulator has transitioned to being totally non-funtional. The car is very hard to start if it has been sitting for about a half-hour.
I have read several threads on accumulators and have come across some suggestions for overcoming the warm start problem, some are mentioned here:
https://rennlist.com/forums/928-foru...re-to-buy.html

I am willing to do some experimenting to find a cost effective solution short of buying a new 928 accumulator.

James Bailey mentions:
“Several feet of rubber high pressure fuel line is said to work.....like your garden hose after you turn off the tap at the house if you squeeze the nozzle it still shoots out a stream of water for a moment. The rubber fuel hose expands a bit and holds a pressure reserve keeping pressure in the CIS system to allow for a easier hot start.”
Anyone here have experience with this? How many feet of what kind of hose?

He goes on...
“When cold the ninth fuel injector gets the fire going and the airflow triggers the injection. Some have mounted a push button to turn on the cold start injector anytime they wish which eliminates the need for the accumulator....”
That sounds cool… eliminating the accumulator, how is that done exactly?

Jadz928 has this suggestion:
“For those looking for an alternative for the NLA early-style accumulator (0438170022) consider Bosch 0438170031 - used on the later CIS 911 Turbos. It's readily available, can be had under $150, and has the 14mm vent fitting. The inlet and outlets are 14mm male. You will need a 2 custom fuel lines w/ 14mm female adapters (in conjunction w/ AN fittings). Note: If you desire to preserve the original S-shaped hard-line that goes btw the accum outlet & fuel filter, you will need to hunt down a 16mm female inverted flare to 14mm female adapter. This will be hard to find.”
I like this one, it keeps the system close to stock for a reasonable price. In my setup seen here…



… it would be possible to replace the accumulator input with an extension from the existing hose coming from the fuel pump, ending in a 14mm female fitting. An adaptor from the accumulator output to the fuel filter hard-line would be needed. From what Jadz says that would be 14mm male at the top (new accumulator end) and 16mm female at the bottom (fuel filter hard-line).

ROG100

There are at least three reasonably priced alternatives but they have male connections. I have never been able to find the adapters to make them fit - male to male 14mm.
Price about $175 but then you have the problem to connect to the existing pipework.
The original (026) is not that expensive at $227 and I have them in stock.

STRIKEMASTER

Maybe a stupid question, but I'll ask anyway: If it's the diaphragm in the fuel accumulator that fails, has anyone tried to replace the diaphragm? Grind off the crimped over edge, separate the 2 halves, replace the rubber piece and make a set of 'ring clamps' to bolt it back together ?? From the cut-away drawings I've seen, it 'looks viable". What say 'The Pros from Dover'??

Guy

When I first bought my 928, I really hustled to save very dollar. Tried all kinds of shortcuts to save money as I didn't want to dump a lot of money into the car until I had a sense of the total projects needs. What I did learn is that the more shortcuts you take, the more variables you introduce into an already complicated system. Some things are best worth doing once and moving on knowing that it is checked off your list once and for all.

if your car is a keeper, I would replace this critical component and save the bucks elsewhere on the car.

hwyrnr

I agree with GUY on getting the right parts for critical systems.

And with the prices ROG listed, if you get the $175 part then have to source adapters and spend let's say $25 for the adapters and shipping you mine as well spend the extra $25 and get the $225 part that fits and save your time and headache.

And im one of those guys that are on a strict budget. But figured out quickly with this car sometimes you save up a little extra and buy the correct part. I might have to wait another pay period, but when it's installed then I feel more confident that problem is taken care of.

skpyle

Well said!

dr bob

FWIW, there are several possible causes for the warm hard-to-start beyond the accumulator. Test the accumulator by blocking the outlet with a pressure gauge fitting. Run the pump with a relay jumper. Watch the gauge to see if the accumulator and check valve hold. Blocking the outlet with the gauge isolates the accumulator and check valve from the rest of the places that too often leak by and bleed pressure.

-- The warm-up regulator is a most popular cause of pressure bleed down.

-- The main pressure regulator in the fuel metering unit (often referred to as the "fuel distributor")

Effective diagnosis demands a disciplined approach to testing components. The CIS pressure test gauge set is an absolute must for any reasonable troubleshooting effort. Roger at 928SRUS offers them, and there are sets around in the normal commercial channels. There may be a set available near you to loan if you ask.

The 928 factory workshop manual offers some basic guidance on CIS system troubleshooting. IIRC there's an expanded technical publication from Porsche on the system. The "bible" is probably the Probst book, available from most booksellers. I urge you to arm yourself with at least the WSM guide before you get too deep into just blindly replacing things. At hundreds of dollars per test component, it can get really expensive in a hurry.

FWIW, almost every CIS "problem" I've come across is caused by dirt or corrosion. If there is a system on the cars that really rewards regular use/driving, it's CIS injection.

V2Rocket

not super familiar with CIS so maybe just making noise here..

but after a brief read-up on the accumulator function it would seem the intended functions:
- keep pressure up to prevent fuel boiling on a hot, shut-off engine
- smooth pressure pulses from the fuel pump

...could be accomplished by fitting a pump check valve and L-jet fuel pressure regulator?
- check valve obviously prevents fuel bleed-down
- FPR say 2.5bar would keep pressure after it at 2.5bar even if the system is off to avoid boiling.
--- but since the CIS system runs at higher pressure than that once it's actually running the 2.5 bar FPR diaphragm would be sitting "wide open" letting fuel thru (as if it were trying to bleed off excess pressure from a fuel rail)

elgy

This is my temporary work-around, since the car is going into winter storage at the end of the month.



A fused jumper to replace the fuel pump relay. I was surprised that with this switch the pump runs even if the ignition switch is off.
This helps the hot start problem, but is not as efficient as I thought it would be. Starting still takes several tries when the engine has been stopped for more than a half hour and less than several hours. My understanding was that running the pump before starting would repressurise the system and make starting like on a cold engine.
What am I missing? Should I let the pump run longer before trying to start?

Meanwhile, I know that the accumulator is bad (it was leaking when I did my rear fuel hoses during the summer but still held enough pressure to help starting. Now it seems to be definitively finished) so I will probably buy a new accumulator for installation during the winter.

upstate bob

I would think that an accumulator for a 1985-86 VW Jetta or Golf could be adapted. They had a similar CIS Bosch system. Fuel flow rates shouldn't be a factor. The big thing with these buggers is the
little check valve. Usually clean that out and they come back to life. I wouldn't attempt a used accumulator because those rubber parts only last so long.