911 SC Fuel Pressure Accumulator and check valve.

[Bill Douglas]

And is there another one on the CIS fuel distributor?

The 1982 SC Euro takes a few moments before it fires up from cold. Whereas in the past it fired up straight away.

I've replaced the fuel pump check valve as part of the new fuel pump assembly, and a new fuel accumulator. It starts well, but not instantly like it has done in the past. If I remember correctly there is another bit to swap out on the fuel distributor itself?

Thanks Guys!

[proporsche]

how is your sensor plate position? possibly a little backfire will knock it off the center..if yes it would change your fuel mix.

Ivan

[Bill Douglas]

Thanks Ivan, I'll have a look at that.

I need to get some window switches from our host and I'm thinking I'll get a few more bits I may need while I'm at it.

[SkiVT]

Look at the Primary Pressure Valve on the FD. It has some rubber gaskets that can leak.

[Reiver]

Originally Posted by Bill Douglas

And is there another one on the CIS fuel distributor?

The 1982 SC Euro takes a few moments before it fires up from cold. Whereas in the past it fired up straight away.

I've replaced the fuel pump check valve as part of the new fuel pump assembly, and a new fuel accumulator. It starts well, but not instantly like it has done in the past. If I remember correctly there is another bit to swap out on the fuel distributor itself?

Thanks Guys!

Bill, my '83 930-10 is like that too and...I like it. Something bleeds down when fully cold and a long overnight. More than likely some old injector seals. When started and warm it fires right up. I just turn the key and pump the gas a bit and it starts cold easily. The injectors are 'sucked in by vacuum when running so no issue there when driving.

Why do I like this....because with the bleed down you will not have fumes/fuel in the lower air box that can cause a backfire event.

I was initially going to fix it but it does not get worse....and I believe can save me from buying an airbox.

I have an onboard AFR gauge and the fuel delivery system works perfectly in the manner I have set the AFR.

[Bill Douglas]

Thanks Guys!

Maybe I will leave it. I pump the gas a bit too and when It begins to fire up I take my foot off and it starts up fine.

[moparrob]

No 'pumping the gas' on a CIS car. It should start by reaching in the window and turning the key.

[boyt911sc]

Originally Posted by moparrob

No 'pumping the gas' on a CIS car. It should start by reaching in the window and turning the key.

For CIS and other fuel injection systems, pumping the gas is not necessary. For carburetors, yes but not for fuel injection systems.

Tony

[Reiver]

Originally Posted by moparrob

No 'pumping the gas' on a CIS car. It should start by reaching in the window and turning the key.

We know that...we are discussing a different issue and a way around as having a dry airbox when starting cold is a good thing.

IOW, I at least, like the idea of a slight fuel purge before a cold start with CIS as that makes a backfire next to impossible.

That fuel purge is, in my case, a few not properly sealed injectors when off. This allows fumes and fuel to evap from the airbox etc. over nite. A pump of the accelerator, in this case, makes it start properly.

The injectors seal under vacuum no issue and my on board AFR indicates a perfectly running system after the start.

I want that slight air leak. I'll never blow a box.

[proporsche]

Bill..of course the best way to find your problem is fuel press gauges ....
addicted by me..cliping the lines is for hot start problem not for cold start

Ivan

[Bill Douglas]

I've been looking at pic's of the Primary Pressure Valve on the FD and may pull the part out and replace the O rings. Do you guys know where it is on the fuel distributor and can I just unscrew the part? Thanks for your interest in this.

[proporsche]

here.it is ..

[Bill Douglas]

Originally Posted by proporsche

here.it is ..

Thanks!

[PeteKz]

If my memory serves correctly, per Charles Probst in his Bosch Fuel injection book: in later CIS systems, like yours, the pressure regulator has a "push valve" built into it. It closes to capture system pressure at shutdown. Maybe that is leaking down slowly, but as proporshce mentioned above, you need to measure pressures to see what's happening.

If it starts up in a couple seconds, it might not be worth messing with. You know the old rule, "If it ain't broken, don't fix it."

[Schulisco]

Hard (cold) start on a CIS car is always a matter of (wrong) mixture. Either too lean (e.g. caused by too high control pressure, too low fuel system pressure, first and foremost due vacuum leaks) or too rich (too low control pressure, a non opening AAV, flooding cold start valve, misaligned sensor plate, etc.).
I guess that since the problem occurred nothing else has been done as to replace the check valve and fuel accumulator (which is a good approach from my point of view and experience - they can also cause a hard (cold) start!) and this also made the start even better but it's still not perfect again as before. So - if the sensor plate adjustment hasn't been touched since then this shouldn't be the culprit.
Check for vacuum leaks as they can easy make the most problems on CIS cars. Also check the fuel systems pressure as already mentioned and the WUR control pressure (which is the 2nd most issue for a hard (cold) starting CIS car. Do not replace/change anything until it's measured/checked/proved that the part is out of spec/defective/wrong.
Check the AAV if it opens up on cold and getting closed when warm. Check also both vacuum (flying saucer/disc) valves (deacceleration valve and cold start valve) on the right side of the engine close to the fuel distributor. Check procedures can be found here in the forum.

Thomas

[boyt911sc]

Originally Posted by Schulisco

Hard (cold) start on a CIS car is always a matter of (wrong) mixture. Either too lean (e.g. caused by too high control pressure, too low fuel system pressure, first and foremost due vacuum leaks) or too rich (too low control pressure, a non opening AAV, flooding cold start valve, misaligned sensor plate, etc.).
I guess that since the problem occurred nothing else has been done as to replace the check valve and fuel accumulator (which is a good approach from my point of view and experience - they can also cause a hard (cold) start!) and this also made the start even better but it's still not perfect again as before. So - if the sensor plate adjustment hasn't been touched since then this shouldn't be the culprit.
Check for vacuum leaks as they can easy make the most problems on CIS cars. Also check the fuel systems pressure as already mentioned and the WUR control pressure (which is the 2nd most issue for a hard (cold) starting CIS car. Do not replace/change anything until it's measured/checked/proved that the part is out of spec/defective/wrong.
Check the AAV if it opens up on cold and getting closed when warm. Check also both vacuum (flying saucer/disc) valves (deacceleration valve and cold start valve) on the right side of the engine close to the fuel distributor. Check procedures can be found here in the forum.

Thomas

Thomas,

The acronyms for AAR and AAV are commonly interchanged due to the translation from original German language to English. This is also evident in several old Porsche literatures and manuals referring to auxiliary air regulator (AAR) as auxiliary air valve (AAV).

The auxiliary air valve you are referring is called in this part of the world as AAR(auxiliary air regulator) that is normally open when cold and gradually closes when heated. The AAV is the saucer-like device that is not dependent on heat or temperature.

Your understanding about the device is correct except we refer to it as AAR and not AAV. My two-cents.

Tony

[7783911]

what size are the replacement gaskets as per SkiVt
"Primary Pressure Valve on the FD. It has some rubber gaskets that can leak."

thanks

I too have hard hot starts (sometimes), the fule distributor was out and test when the top end was rebuilt. the fuel accumulator and the FP check valve are good. According the the race shop I use, fuel pressure was tested OK as well. so I am running out of ideas

[SkiVT]

No idea if these are universal size or specific to the FD. They seem to be included in some full FD rebuild kits. Examples below I found with just the o-rings. Again, no idea if the size is correct.

https://www.ebay.com/itm/184445549660

https://www.deloreango.com/us/hot-start-o-ring-kit.html

[7783911]

Thanks SkiVT

I ll give that a try

ps..I grew up skiing Jay Peak

[Schulisco]

Tony,
thanks for your comment, you're right. In german the AAR is either called "Zusatzluftschieber" (a "Schieber" is a synonym for valve (or slide valve) in German) and valves in german are generally named as "Ventil" = "valve".

Here's my corrected version:
Check the AAR if it opens up on cold and getting closed when warm. Check also both vacuum (flying saucer/disc) valves (deacceleration valve and cold start valve aka "AAV") on the right side of the engine close to the fuel distributor. Check procedures can be found here in the forum.


Thomas