CIS air censor oscillation.

[fanaudical]

OK - Different engine/CIS setup from stock makes sense. Are all the CIS components still matched for the '77 engine? (FD's and WUR's need to be matched, I think, to keep things running as expected.)

I'd be surprised if it's the AAV as it can't really change position fast enough to cause something like this. You might check the vacuum module on the distributor as well.

[allaircooled]

Well, I pull a 6-8" vacuum on the AAR following the directions of another thread on how to test. I have vacuum on the larger port and finger on the other. Release the finger and vacuum is gone instantly. According to the testing procedure I was reading, that would make this unit bad?

Edit: I did some more testing and I need 16" of vacuum to get it too hold.

[T77911S]

are you talking about the aux air VALVE (AAV). its the big round disk on the rear.
if so, one port pulls the diaphragm in and holds it, the other one will not. when I tested mine it was a bear to get it to pull in but it would hold once pulled in.
depending on how big the leak is and if it will pull in at all determines its effect. it will only effect idle/ rpm's, not AFR issues. not sure what it do while driving. never considered this before but once the RPM's get hi and vacuum drops it should open anyway.
its there to aide is starting. its like putting your foot on the gas to start it.

the AAR is controlled by 12v. it is open while starting and after but only when cold. it closes once warm.

the 033 WUR uses vacuum to control the CP. with vacuum the CP is 3.6, without its about 2.8br.
if you have a hand vac pull a vac on the lower chamber. it should hold.

the decal valve (DV) can leak, again it just effects idle. I removed mine. I was getting oil blowby and it was actually filling up in the DV causing it to hang open raising the idle.
never cared for it. also removed it from my 930.

[boyt911sc]

Originally Posted by allaircooled

Well, I pull a 6-8" vacuum on the AAR following the directions of another thread on how to test. I have vacuum on the larger port and finger on the other. Release the finger and vacuum is gone instantly. According to the testing procedure I was reading, that would make this unit bad?

Edit: I did some more testing and I need 16" of vacuum to get it too hold.

Chris,

A typical 3.0 liter SC can conveniently produced 22" Hg of vacuum. I used 15"-~ 22" Hg for my tests with thermotime valves, decel valves, brake boosters, WUR's, etc. Use 10" (low), 15" (mid), and 22" (high) for your tests.

Tony

[john walker's workshop]

Read post #4 again.

[allaircooled]

Originally Posted by T77911S

are you talking about the aux air VALVE (AAV). its the big round disk on the rear.
if so, one port pulls the diaphragm in and holds it, the other one will not. when I tested mine it was a bear to get it to pull in but it would hold once pulled in.
depending on how big the leak is and if it will pull in at all determines its effect. it will only effect idle/ rpm's, not AFR issues. not sure what it do while driving. never considered this before but once the RPM's get hi and vacuum drops it should open anyway.
its there to aide is starting. its like putting your foot on the gas to start it.

the AAR is controlled by 12v. it is open while starting and after but only when cold. it closes once warm.

the 033 WUR uses vacuum to control the CP. with vacuum the CP is 3.6, without its about 2.8br.
if you have a hand vac pull a vac on the lower chamber. it should hold.

the decal valve (DV) can leak, again it just effects idle. I removed mine. I was getting oil blowby and it was actually filling up in the DV causing it to hang open raising the idle.
never cared for it. also removed it from my 930.

Reason I even checked my AAV is because I never checked it and thought why not. I also read in the CIS Primer that one of symptoms of failure was idle oscillations. So, I figured it wont hurt to check.

Chris,

A typical 3.0 liter SC can conveniently produced 22" Hg of vacuum. I used 15"-~ 22" Hg for my tests with thermotime valves, decel valves, brake boosters, WUR's, etc. Use 10" (low), 15" (mid), and 22" (high) for your tests.

Tony

Ok Tony, only thing that concerned me about this is the spec was 8". Doesn't matter now, after a few times putting a 16" vacuum on it, it now closes and holds a 8" everytime. Don't know if it was stuck or whatever.

Read post #4 again.

Yes sir, I didn't forget your post. There was some doubts from others trying to help and I just wanted to make sure it isn't anything else before I send it off.

thank you all.

[john walker's workshop]

Don't send it off, just find another one. Lots of them out there.

[boyt911sc]

Originally Posted by john walker's workshop

Bad fuel distributor.

John,

The FD-006 was tested and confirmed GOOD. Ran the FD with no injectors installed and not a single drop. And the plunger was lifted to measure the flow rates of the six (6) ports. All six (6) delivered consistently very similar volumes of fluid and repeated the test multiple times. I have great respect for you but sorry you have guessed it wrong this time.

Tony

[boyt911sc]

Chris,

I did a test of the AAV's not too long ago using one of the two boxes of AAV's in hand.





The lowest vacuum that could close and seal the AAV the better. It is open at atmospheric pressure and once the engine starts to run, the AAV closes as the engine develops vacuum. You don't need the 10",15", and 22" Hg I mentioned for AAV. These vacuum are used for the decel valve, TTV, and WUR. Less than 5" Hg. will close a good AAV. I have yet to find a bad AAV. The DV (decel valve) is different. It fails more often than an AAV.

Tony

[allaircooled]

Originally Posted by boyt911sc

Chris,

I did a test of the AAV's not too long ago using one of the two boxes of AAV's in hand.





The lowest vacuum that could close and seal the AAV the better. It is open at atmospheric pressure and once the engine starts to run, the AAV closes as the engine develops vacuum. You don't need the 10, 15, and 22 psi. I mentioned for AAV. These vacuum are used for the decel valve, TTV, and WUR. Less than 5 psi. will close a good AAV. I have yet to find a bad AAV. The DV (decel valve) is different. It fails more often than an AAV.

Tony

Yeah Tony, maybe I wasn't clear, but I found mine to be good. Like I mentioned, at first it wouldn't close until 16" of vacuum, but now it is closing at 8" and holding which is spec for my particular AAV. I am moving on.

[boyt911sc]

Originally Posted by allaircooled

Yeah Tony, maybe I wasn't clear, but I found mine to be good. Like I mentioned, at first it wouldn't close until 16" of vacuum, but now it is closing at 8" and holding which is spec for my particular AAV. I am moving on.

Chris,

A good working AAV will close at 2 psi. (vacuum). And once it is closed and sealed, additional vacuum is not necessary or needed. However, if your good AAV did not close @ 16" Hg there was something wrong with your test. I have 2 boxes of these AAV's and have yet to find a bad one. The only time a AAV failed for my tests was that the plug was not properly installed. It is good to test it to confirm that it is not the culprit. Some people like to guess and sometimes they get lucky. But you can not rely on luck alone for diagnostic troubleshooting.

Tony

[allaircooled]

However, if your good AAV did not close @ 16" Hg there was something wrong with your test.

Thanks for the confidence haha. I am pretty sure this was one of the easiest things to test, not very complicated.

I tested the decel valve too. It opens at around 15". Seems good to me too.

[john walker's workshop]

Originally Posted by boyt911sc

John,

The FD-006 was tested and confirmed GOOD. Ran the FD with no injectors installed and not a single drop. And the plunger was lifted to measure the flow rates of the six (6) ports. All six (6) delivered consistently very similar volumes of fluid and repeated the test multiple times. I have great respect for you but sorry you have guessed it wrong this time.

Tony

Maybe. Been wrong before, but we'll see in the end, it ain't fixed yet.

[fanaudical]

I think opening spec on the decel valve is ~22"Hg. You want this closed at idle.

[T77911S]

the problem with the FD's and oscillating is internal to the FD. nothing to do with metering of fuel to the injectors.
it has to do with the pick off circuit for the CP to the WUR and that fuel path.
I am all for testing other things to be sure but when you get to the end of the list you have to go back to the FD.



I am more for having it rebuilt than buying a used one unless you can be sure you are not getting another bad one.


tony probably has a spare he can send you to test on your car.
did you test the OP;'s FD or did he test it

tony, that's a lot of AAV's, you have a problem my friend. seek professional help.

[john walker's workshop]

The reason I mentioned getting another used FD is that the rebuild procedure doesn't fix the damaged oriface at the top of the bore. No way to get at it and no replacement part. Fixed this problem multiple times and it was always the FD. Just got another used one off the shelf and problem solved.

[allaircooled]

Originally Posted by T77911S

the problem with the FD's and oscillating is internal to the FD. nothing to do with metering of fuel to the injectors.
it has to do with the pick off circuit for the CP to the WUR and that fuel path.
I am all for testing other things to be sure but when you get to the end of the list you have to go back to the FD.



I am more for having it rebuilt than buying a used one unless you can be sure you are not getting another bad one.


tony probably has a spare he can send you to test on your car.
did you test the OP;'s FD or did he test it

tony, that's a lot of AAV's, you have a problem my friend. seek professional help.

Well, I am already at the end of that list. I know Tony swears it is not the problem, but you and Mr. Walker seemed convinced that it is. I think I will start looking for a FD today. I have been at this problem off and on way too long.

I think opening spec on the decel valve is ~22"Hg. You want this closed at idle.

According to the CIS primer web site, it says around 14".

[T77911S]

Originally Posted by john walker's workshop

The reason I mentioned getting another used FD is that the rebuild procedure doesn't fix the damaged oriface at the top of the bore. No way to get at it and no replacement part. Fixed this problem multiple times and it was always the FD. Just got another used one off the shelf and problem solved.

correct. I thought when larry rebuilds them he can fix that issue.

[boyt911sc]

Chris,

Before you decide to spend and buy a replacement FD-006, I would suggest that you try one of my FD-006. This is not a rebuilt unit but one of the several good FD's from my collection. PM me if you are interested. Just return it back to me after the test.

Tony

[fanaudical]

According to the CIS primer web site, it says around 14".

I've seen that in the CIS Primer but it doesn't make sense to me to have the decel valve open at idle.

I have a scanned copy of an older Porsche workshop manual. It indicates that the valve should not be allowing air to bypass at idle and should only allow air flow under high vacuum conditions. I went back and looked through this and my Bosch manuals for where I got the 22"Hg opening spec; I can't find it. I think I set that empirically last time (my 2.7 idles ~20", I added 2" for margin).