Need CIS help... of course

[Schulisco]

Originally Posted by McGalliard

Or is it that the spring is macro-adjustment and the mixture screw is micro-fine tuning?

^^THIS^^

I thought the mixture screw controlled a bypass channel of some sort.

No, that is the idle screw!

I have the whole set of Porsche repair manuals and several Bosch service guides, so I guess I should find the source reference and follow the instructions.

The problem on all these documents is that most of them explain every components function but not so much how they interact and when or what time they're active. This knowledge you only get by working on the CIS. The only thing I can recommend is the CIS troubleshooting guide:
https://cis911primer.com/Troubleshooting%20Guide/Notebook%20Spiral.html

Here's s thread we had one year ago about sensor plate height, maybe this help you to underdtand...
https://forums.pelicanparts.com/porsche-911-technical-forum/1158127-air-sensor-plate-height-why.html

[McGalliard]

Originally Posted by Schulisco

No, that is the idle screw!

And now I have learned these are actually two different things. Thanks, as always.

As for driving through a couple tanks of fuel and additive, my mechanic has advised against that based on the current fuel mixture and smoke issue. So I guess the next step is double check/set the plate height and then smoke test for leaks? Maybe simultaneously getting the WUR rebuilt?

[Schulisco]

Do only one thing at the time. Otherwise you're running into trouble mixing up things and losing oversight.
And prove any bad part by testing it before replacing as todays parts quality mostly no more same quality as in early days...

[Schulisco]

In this thread we discussed in more detail about sensor plate height. This posting I added a sketch from Bosch tech instruction manual about CIS on how the sensor plate house is in detail:
https://forums.pelicanparts.com/porsche-911-technical-forum/1158127-air-sensor-plate-height-why.html#post12203447

Whole thread is worth a read.

[McGalliard]

Originally Posted by Schulisco

Do only one thing at the time. Otherwise you're running into trouble mixing up things and losing oversight.
And prove any bad part by testing it before replacing as todays parts quality mostly no more same quality as in early days...

I do understand the principle. I am expecting that when it’s warm enough here to compare pressures to the graph, someone will tell me my WUR needs rebuilding. But I won’t do that until confirmed. If the plate height is really just supposed to be set to a height and left, not adjusted or dependent on other factors, then that can be checked/done independently. If there are vacuum system leaks, those too should be fixed regardless. I guess I’m just trying to get back to baseline to then make proper adjustments. Seems to me there are only so many parts and fewer of them are “adjustable”.

[McGalliard]

Latest round of pressure testing, basically done at 10 deg C, the bottom of the temp/pressure charts.

CCP - 1.6 bar
SP - 4.55 bar
WCP
@ 4.5 min - 2.7 bar
@ 7.0 min - 2.95 bar

So it would seem CCP is a touch high. SP is in the lower end of the normal range. And my notes say WCP should be 2.9-3.1 bar, which it eventually is but maybe it needs to get there in 3-4 minutes instead of 7 min. Does it matter that it takes a little longer to plateau at that level? These numbers obviously aren't as bad as we originally thought. Doesn't feel to me like they are so out of whack as to be the source of hard cold start, rough early idling, and a poor air/fuel mixture.

Where do I go from here?

[Schulisco]

Check how many turns you need to fully close the idle screw. Turning CW closes the idle screw bypass, CCW opens it.

[Johner]

I wouldn't worry about the long.time to get the wcp in spec. I found the same.thing when performing this test on battery power and low ambient temperature. When I repeated the test with the engine running the WCP got into spec in about 3 minutes.

I would follow Schulisco's advice on checking the idle screw, and if you haven't already done so, get set up to do a vacuum leak test. There are multiple threads on how to do this, but let us know if you need a link. I wouldn't adjust anything until you confirm no vacuum leaks.


John

[fanaudical]

I'm going to make a few statements that others may not agree with. Here goes:

Low ambient temperatures may make testing the fuel pressures difficult. If you don't have a heated garage, it may make more sense to ignore that for a bit and focus on eliminating unmetered air until the ambient temperatures rise. The important part: Focus on one or the other - not both. If you start chasing air leaks then please ignore system pressure and control pressures for a while.

I have used two different methods to reliably find air leaks:

#1 - Smoke test with a smoke machine - Lots of threads here on that. Cap the exhaust pipe, remove the air duct and cap the throttle body, connect a smoke machine to a vac port on the air box, and watch for leaks.

#2 - Soapy water with the shop vac test - Remove the air duct and cap the throttle body. Connect a shop vac in blow mode to the tailpipe. Spray a little soapy water on all joints (including every air box seam and connection) and watch the bubbles.

CAUTION: For both tests, you want to limit the air pressure inside the intake system to a couple inches of water or else you will damage things.

You need to treat the air leaks and pressure issues as two separate issues. Fix one, then the other. Checking / fixing air leaks first makes sense as you then only have to set the idle/mixture and ignition timing once.

While you're in there, you can make sure the air flow metering plate rests where it should and is centered in the bore.

Everything from here on out assumes the air leaks are sealed (as well as they get).

Originally Posted by McGalliard

Latest round of pressure testing, basically done at 10 deg C, the bottom of the temp/pressure charts.

CCP - 1.6 bar
SP - 4.55 bar
WCP
@ 4.5 min - 2.7 bar
@ 7.0 min - 2.95 bar

So it would seem CCP is a touch high. SP is in the lower end of the normal range. And my notes say WCP should be 2.9-3.1 bar, which it eventually is but maybe it needs to get there in 3-4 minutes instead of 7 min. Does it matter that it takes a little longer to plateau at that level? These numbers obviously aren't as bad as we originally thought. Doesn't feel to me like they are so out of whack as to be the source of hard cold start, rough early idling, and a poor air/fuel mixture.

Where do I go from here?

Question #1: Did you ever validate your pressure gauge against another known pressure gauge? If not, please do so (just to ensure the pressure readings are meaningful).

My opinion (which assumes that you have a good, working gauge): Your system pressure is on the bottom edge of the limit and needs to be adjusted back up toward the 4.9 bar range as a starting point. CCP / WCP don't matter unless the SP is correct.

Question #2: Do you have vacuum applied to the WUR for your test? If not, you need to (and see the WUR chart for the correct vacuum amount).

The -009 WUR uses a vacuum enrichment system: Vacuum drops at wide open throttle, the control pressure drops, the air sensor raises a little extra, and you get richer fuel mixture when you need it.

Please retest with both vacuum applied and without and report both. It's relatively easy to do - Hook a vac pump to the vac fitting. Apply/release vacuum when cold and again when warm.

Summary for the next pressure test:

#0 - Wait for warmer temperatures and seal air leaks while you wait; put the air flow plate in the correct position. This won't affect the pressure test but it will affect drivability eventually and you will make progress.

#1 - Validate the gauge is good.

#2 - Get system pressure back toward the top end of the setting spec.

#3 - Test control pressures with and without vacuum applied to the WUR.

#4 - Report back.

Once we've got air leaks sealed, air metering plate in the right place, and a confident pressure test - then we can figure out what needs to be adjusted.

[McGalliard]

Originally Posted by Schulisco

Check how many turns you need to fully close the idle screw. Turning CW closes the idle screw bypass, CCW opens it.

4 full turns to close the idle screw.

I believe the AFSP is in the correct position. At rest it is even with the lowest level of the Venturi funnel. So, I'm not going to mess with anything there for the moment.

Vacuum leak testing will occur this weekend hopefully. I will have to get my hands on a manual vacuum gun to redo pressure testing with the WUR under vacuum.

[McGalliard]

Originally Posted by fanaudical

Question #1: Did you ever validate your pressure gauge against another known pressure gauge? If not, please do so (just to ensure the pressure readings are meaningful).

I did cross-check this, but in a not-so-scientific manner. I will do this more precisely in the next few days as well.

Thanks to all for the insights and suggestions thus far.

[Schulisco]

Originally Posted by McGalliard

4 full turns to close the idle screw.

I believe the AFSP is in the correct position. At rest it is even with the lowest level of the Venturi funnel. So, I'm not going to mess with anything there for the moment.

Vacuum leak testing will occur this weekend hopefully. I will have to get my hands on a manual vacuum gun to redo pressure testing with the WUR under vacuum.

4 full turns is way too out by far. The standard setting is 2 turns open from fully closed. With that you're able to start the engine and it will idle when cold with an increased idle of approx. 1200rpms.
4 turns guide me to suppose that sth else is wrong making the mixture that rich.

When you say that the sensor plate/AFSP is set to the lowest end of the venturi funnel, does this complies with this? (bottom schematic)



Thomas

[PeteKz]

Does it run well when fully warmed up and driving?

I'll say again: Spend some time driving it. Put a tank or two of fresh fuel through it (with Techron). You can continue troubleshooting and testing, but some of the glitches may clear up just from using it regularly.

[McGalliard]

Originally Posted by Schulisco

4 full turns is way too out by far. The standard setting is 2 turns open from fully closed. With that you're able to start the engine and it will idle when cold with an increased idle of approx. 1200rpms.
4 turns guide me to suppose that sth else is wrong making the mixture that rich.

So presumably something somewhere else was either adjusted or has failed, leading to an inappropriate correction at this idle screw. I'm guessing the list of possibilities is too long. Does that include vacuum leaks? Or will I likely be hunting down a part in need of a rebuild or replacement?

Originally Posted by Schulisco

When you say that the sensor plate/AFSP is set to the lowest end of the venturi funnel, does this complies with this? (bottom schematic)

Thomas

Yes. I am confident that the sensor plate is exactly where it is meant to be.

[McGalliard]

Originally Posted by PeteKz

Does it run well when fully warmed up and driving?

I'll say again: Spend some time driving it. Put a tank or two of fresh fuel through it (with Techron). You can continue troubleshooting and testing, but some of the glitches may clear up just from using it regularly.

The honest answer really is, " I don't know". It definitely runs better, but it smokes and that make me leary of touring around town with it. I've taken it very briefly down the street and back. But I have zero experience with these cars and their engines, so I don't know what to expect. It is not yet been registered because up until recently it wasn't really running at all. If we're really following the rules, and I tend to be a rule follower, then I would have to register and have it inspected, which then means a list of other odds and ends like lights and seat belts, etc. It can and will be done, but it's not a quick process.

[930cabman]

After fooling with the CIS on my 1975 911S for far too much time I sourced a set of Weber 40 IDT carbs. When new the CIS system was unbeatable, but I just don't have the time patience to fool with it.

Carbs will be at my shop next week, rebuild about a week or so, install a couple weeks. Will be running just in time for spring

Hate to be a quitter, but also interested in enjoying my original paint example

[Schulisco]

Originally Posted by McGalliard

So presumably something somewhere else was either adjusted or has failed, leading to an inappropriate correction at this idle screw. I'm guessing the list of possibilities is too long. Does that include vacuum leaks? Or will I likely be hunting down a part in need of a rebuild or replacement?

Yes, it look's like.
Vacuum leaks - no. As the screw gives with 4 turns double the amount of bypass air to let the engine idling. Even when the mixture seems to be ok, but as you wrote that the engine still smokes. This can be caused by rich mixture as well as burned oil which is common for a flatsix engine after sitting long time. But also detoriated gas may cause this. Depends on the color of the smoke. How does the spark plugs look (color, wet or dry, dirty with black deposits etc.)? How does the fuels smell?

There may be several things to sort, but in the beginning the most important components of the CIS, WUR & FD must be proved okay. So we're back at the beginning.
As I still don't know if your measurings of SP and CP were correct - only when they we're proved correct it makes sense to move ahead to the next steps.
You wrote about your last test results of the CP. Basically they don't look too bad I would suggest to let the FD checked / overhauled by a CIS specialist as they're mostly dead after decades, even if they have been driven or not. They contain rubber sealings, metal sealings and are made of cast iron which can also corrode. The tools you need for overhauling them are highly precise machines you cannot buy at Home Mart...not to mention the experience. Expecially when you aren't experienced with these cars. I got mine overhauled by a specialist and he charged 800bucks 5 years ago...highly satisfied with the work, as the FD is the central component delivering the right amount of fuel to any cylinder under any operating condition which fundamental for a good running car...when some cylinders got too few fuel they run too hot. On an aircooled engine this may cause damages relatively quickly...

But before tearing the FD out of the car I would ask you to do one more thing:
When does your fuel pump start running? When switching ignition on?

[McGalliard]

Originally Posted by Schulisco

Yes, it look's like.
This can be caused by rich mixture as well as burned oil which is common for a flatsix engine after sitting long time. But also detoriated gas may cause this. Depends on the color of the smoke. How does the spark plugs look (color, wet or dry, dirty with black deposits etc.)? How does the fuels smell?

The fuel is new. Most fuel related components are new between the tank and FD except for two polyamide lines. I call the smoke white. I have zero experience with labeling smoke colors though. I don’t think I can begin to accurately describe the smell.

These are the old plugs. Obviously mismatched. I have since replaced them with proper Bosch replacements.

There may be several things to sort, but in the beginning the most important components of the CIS, WUR & FD must be proved okay. So we're back at the beginning.

I already had the FD rebuilt in the Fall. Wasn’t by a CIS specialist per se, but it was someone who specializes in Porsche, Audi, MB, and VW of this vintage. Certainly had familiarity with this part.

I would ask you to do one more thing:
When does your fuel pump start running? When switching ignition on?

Fuel pump comes on when key is put to run position, one stop before cranking for start.

[PeteKz]

I'm reconsidering this. I don't think the CIS is your biggest problem, maybe not even a problem.

Instead, the oil burning would get my attention now. Those plugs you pulled out have a lot of oil on them, and the "white smoke" indicates oil burning. It's time to do a leakdown test.

If you want to keep chasing the CIS, I'll sit down.

[Schulisco]

My experience: Grey/white smoke when engine is still cold is mainly water steam due to unburned hydrocarbons equals too rich mixture, condensed water in the exhaust and detoriated gas. As the gas is fresh I suppose a combo of both rich mixture and condensed water.
If engine is warm and smoke is black the mixture is still too rich. When smoke is blueish on warm engine then it's burned oil...

https://www.autozone.com/diy/exhaust/smoke-from-exhaust#:~:text=Dense%20white%20smoke%20indicates% 20a,of%20which%20are%20good%20signs.

As the 911G has no cooling water within the engine it's pretty clear...

The problem is with idling only in the garage you won't get the engine and the whole oil system and exhaust that warm to get reasonable results...and letting idling or even revving it half an hour or longer annoys the neighbours...and even it's not recommended for the engine (oil pressure and lubrication and even cooling is insufficient)

Check the mounted spark plugs too to see what color the have now. I suppose they look pretty dark too as tge car hasn't been really driven since...

The fuel pump must not run with ignition on on later CIS cars. I remember that the early CIS on '74 and probably '75 too didn't have the security fuel cut off switch at tge sensor plate housing. Check yours if it has one or not. Its a greenish 2pin plug on the "backside".