Fuel Accumulator Issues CIS 3.0 Liter 911

[opticalfuel]

ENGINE: 3.0 Liter CIS - standard CIS Setup...


Just wondered if anyone knows how a fuel accumulator works, and if it's possible to clean / rejuvenate or otherwise fix the component so that is operates as it should again.

I am more curious than anything. I have determined that it indeed is the issue, since my motor starts fine when cold, (cold start valve operates) in the morning, but when warm or hot, and left to sit for 30 min or less (before it is cool enough for the cold start valve to once again operate due to temp) it won't start.

The supporting evidence is that if I keep the key on (fuel pump humming) and manually lift the fuel distributor sensor plate (push up) it causes the fuel lines and injectors to fill back up with the familiar hum ... to whizzzzz... whistle.... ....

Immediately it starts back up, and runs again fine.

Therefore I know it's the fuel accumulator. (Tom Amon believes it's the case after I spoke with him this morning)

I am just curious if anyone knows how it works. If it's a one shot deal, so be it.

I bought a brand new one, as recommended by Tom. He said don't bother with a used one.

But I am still terminally curious.

Thanks all!

[Bob Kontak]

I disagree with your diagnosis only to the extent that the fuel leak bleeding off pressure may not be the fuel accumulator.

Any leak downstream of the accumulator could create the same bleeding off of pressure symptoms.

Since your car starts up if you lift the air sensor you have narrowed it down to pressure loss.

I don't think the accumulator can be rebuilt. Here is a decent description of it's function.

Parts Place Inc.com: VW parts, Fuel Injection, Fuel Pressure Accumulator

Good looking car!

[opticalfuel]

True enough. If I replace the fuel accumulator (which is the OLDEST part in the mix) it'll exclude that from the scenario. If that solves it great... if not, I know I have some work ahead to find any possible leakdown point.

I hope it is resolved with the install of a new F.A. I know it's approximately 10+ years old, and was probably original equipment on my friends '77 911S. It was installed at the same time as the motor, but it could be faulty. It does have a slight kink in the bottom of the main body of the unit... not sure that is normal, but it was that way when i got it, so I did not attempt to straighten it. It's hard to believe that would do it. I don't smell any gas, so I am fairly certain I do not have a leak.

But still there could be a pressure loss in the system.

I'll be sure to report back in the next few days.

Is that kink normal? a problem?

[GothingNC]

Have you considered the check valve at the fuel pump?

Bad check valve can cause the same symptoms as a faulty accumulator.

[opticalfuel]

Yes... I did purchase a new fuel pump, and I believe it comes with a new check valve. If it's a new fuel pump (within a year - new when motor installed) I should be ok there right?

[Bob Kontak]

I don't think that bend hurts anything - unless the pressure check seal is right there - then your theory is getting real, real strong.

Could be the cold start valve or the injectors leaking but you probably have it nailed with the F/A. I am not sure if the F/A is working right if the fuel pump check valve can cause an issue - but I defer to GothingNC's advice.

Given you don't have fuel leaks, follow up checks are the injectors and the cold start valve. Beyond that you have the fuel return line system. Injectors are easy to test. Cold start valve a moderate PITA to remove and observe. Fuel return system - I don't know how to check that. You will have to read up on that. There has to be a check valve somewhere - maybe in the fuel dist itself?

[boyt911sc]

Originally Posted by opticalfuel

ENGINE: 3.0 Liter CIS - standard CIS Setup...


Just wondered if anyone knows how a fuel accumulator works, and if it's possible to clean / rejuvenate or otherwise fix the component so that is operates as it should again.

I am more curious than anything. I have determined that it indeed is the issue, since my motor starts fine when cold, (cold start valve operates) in the morning, but when warm or hot, and left to sit for 30 min or less (before it is cool enough for the cold start valve to once again operate due to temp) it won't start.

The supporting evidence is that if I keep the key on (fuel pump humming) and manually lift the fuel distributor sensor plate (push up) it causes the fuel lines and injectors to fill back up with the familiar hum ... to whizzzzz... whistle.... ....

Immediately it starts back up, and runs again fine.

Therefore I know it's the fuel accumulator. (Tom Amon believes it's the case after I spoke with him this morning)

I am just curious if anyone knows how it works. If it's a one shot deal, so be it.

I bought a brand new one, as recommended by Tom. He said don't bother with a used one.

But I am still terminally curious.

Thanks all!

optical,

FA (fuel accumulator) is one of CIS component easiest to check. It has a membrane (diaphragm) that separates the lower and upper chamber of the FA and an internal spring. It acts as a damper device for the FP and help keep the residual pressure for an extended time provided the FP check valve does its job.

The most common failure of a FA is ruptured or damaged diaphragm causing the fuel to leak. You can test residual pressure for check valve and FA. A simple test for FA is pressuring it with air or putting fuel into it. Or you could blow air by mouth and feel any air coming out from the bottom port (other top port plugged by your thumb).

Installing a used FA is acceptable if you test it before using. Same with FP. It is imperative that you use a fuel pressure gauge in diagnosing problem for fuel injected system. Keep us posted.

Tony

[Bob Kontak]

Tony, thanks for the tip on FA test. Keep it simple.

Reminds me of the post where someone wanted to test their CSV recently and I did some searches and found you can test it by lifting up the blow out flapper in the air box and look for the spray. Duh. I had taken mine out once to test.

[GaryR]

Originally Posted by Bob Kontak

Tony, thanks for the tip on FA test. Keep it simple.

Reminds me of the post where someone wanted to test their CSV recently and I did some searches and found you can test it by lifting up the blow out flapper in the air box and look for the spray. Duh. I had taken mine out once to test.

You also have to be cranking the motor during that test for the CSV to function, yes?

[opticalfuel]

The bottom line is that one or more components or connections in the fuel pressure system is/are allowing the FP to bleed down (or the heat from the engine is causing vapor lock - which is another condition which happens when there is a lack of FP. The temp of the engine is usually around the boiling point 200, and it just converts the fuel that had been flowing into the injectors into vapor, since there is a lack of FP to maintain it in a fluid state)

The result is what I have been able to observe which is after obtaining operating temp, and stopping for a period of time (usually 15-20min) the car won't start, but just turns over rapidly, not catching. It acts exactly as if it's out of gas. Then if I turn the key on, manually lift the air sensor plate inside the air box, you hear the famliar weeee----shss wwhhhirrrrrsqueeelelllll..... AND then it WILL start, but stumbles on 4-5 cyl, then 6, then smooths out. Basically it goes from lean mix to normal, and then runs perfectly.

When cold... It relies on the CSV, which does work, since it will start reliably in the morning, but AGAIN, it starts up very rough, as if there is no gas in the lines to the injectors.... but there is some that has turned back into a liquid form, as it had plenty of time to cool.

Solution: Diagnose and resolve the loss of F.P. which could be as simple as the test above, with the F.A. then investigate further if necessary. The loss of pressure is key. Once I have eliminated that leak point (introduction of air, or drawdown in pressure) it will start reliably and work perfect.

I'll let you know how it runs as soon as I do more research. I should get a brand new F.A. today or tomorrow, and it'll quickly become apparent if that solves it or not. Then I can go further if necessary.

Cheers.

[Targa4now]

subscribed for obvious reasons!

[Bob Kontak]

Originally Posted by GaryR

You also have to be cranking the motor during that test for the CSV to function, yes?

Yes - a second person turns the key unless you rig up a remote starter.

[opticalfuel]

has anyone ever wired in a backup momentary switch to the CSV, which would simply hotwire the starting process by allowing manual operation when starting (if needed)?

It would be a work around, but it would eliminate the need to pull off the air cleaner, push up the plate with the key on...etc.

I know, I know... it's sac-relig.... and I should always fix it right, but as far as a backup... it'd be nice.

I imagine all you have to do is wire in a +12 to the correct wire to manually charge the injector, and you'd have a spirt of fuel at the push of a button. Does anyone have any thoughts on that? I have heard it has been done.

[T77911S]

that car does not suit you. you should really upgrade to something nice. i will be more than willing to take that hideous car off your hands, not to mention all the problems you are having. just think, no more problems with a nice new shinny one.


make sure the new FP came with a new check valve. that is much cheaper than a FA.

[Bob Kontak]

Flagrantly and abhorrently hideous. That is without mentioning those silly looking wheels.

[opticalfuel]

Originally Posted by Bob Kontak

Flagrantly and abhorrently hideous. That is without mentioning those silly looking wheels.

Agreed! I can barely stand to be seen driving this horrifying wreck of a car!!!

... but somehow I maintain my composure...

HEY!!!



Fedex just dropped off my new F.A.!!!


I will pop it in, and report back this afternoon. It'll either work - or it won't.

We'll all know soon.

[opticalfuel]

Ok. --- NEW F.A. installed and ready for blastoff!

I will report after I return this afternoon. It should be very evident if it works or not.

Curious: I was pouring out the residual gas from the original F.A. and out popped what looks to be the remains of an old bee hive (or a fragment of one. NOT good.

I don't know how that could have gotten in there.. unless it sat in a barn or garage for years. ---- it could be... but at least its gone now.

[opticalfuel]

So far... so good. NO issues. I haven't tried to start it hot yet... but will soon - need to wait about 20 min.

[Bob Kontak]

Hope this works for you.

[opticalfuel]

Just tried it again after leaving it for about 1 hr or more and it started right up, without any problem. Two or three rotations, and it goes to idle. It was fully warmed up as I had driven 20 miles away... then parked it for an hour. Previously - this would have never started that easy.

Seems to have worked perfectly... I will do a followup this evening.

Looking good!