CIS Sensor Plate Height

[targa80]

I don’t know what the average turns are on an adjusted idle mixture screw. But, I do know that once I removed all of the vacuum leaks I had to adjust the idle screw from closed to open to raise the idle to 950 RPM where before it was closed and the idle was stuck at 1200 RPM’s. Also, with the idle set correctly at 950 RPM’s remove the oil filler cap this will introduce false air into the vacuum system. The engine idle will drop slightly but the engine should still run and not stall. If it stalls then you probably still have a vacuum leak somewhere in the system.

I would like to add my story about a high idle after deceleration issue to this thread. My model AAV has the open air/vacuum line port so my car looked like it had two Decel valves installed. Someone prior to me connected the vacuum port from this AAV to the Decel vacuum port and eliminated the vacuum line that connected to the throttle body and cruise control. I guess this was done due to a high idle issue after decelerating.

This is the way mine was configured.



This is the is the correct configuration of the Decel and AAV valves for my model.



This photo shows an AAV without the air/vacuum port. I consider this to be what you would find on a typical 3.0 engine setup.



My model AAV is a 404 with the open air/vacuum port. I did test this unit and it did function as an AAV.



Once all the vacuum leaks were eliminated, the vacuum lines were installed correctly and the CIS was setup to within testing specs I now had the high idle after deceleration. The tech article describes how to slightly crush the Decel valve to eliminate the high idle after deceleration. I did adjust the decel valve as described in the tech article and it eliminated the high idle issue.



Over the years I have read threads where someone will say disconnect this or that because it is not needed or it is causing a problem and in many cases they are just masking a problem. Granted, these engines have had ancillary systems installed to reduce carbon emissions over the years and in many cases reduces the performance of the engine. In my own case I believe that the CIS with Lambda that is installed in my 80SC when properly maintained does perform flawlessly.

[Schulisco]

Saw your last video.

The overall problem is: There are so many opportunities to "(fine) tune" the mixture on the CIS that you can make it that the engine willl start good, but run poorly, or to start poor and run good and so on. You can only identify the root cause by searching step by step, following the manuals and the basic settings from Porsche. This means follow these instructions in exactly this order:

1. The basic setup for the idle screw is fully closed and then open it back with 2 turns! If this is not working, then there's still another problem(s). When you only turn 1/2 and engine runs good, the mixture is too lean.
2. Basic setup for the CO screw: Turn the CO screw almost completely in (clockwise) out / counterclockwise, switch on fuel pump (sitting engine, WUR electrically disconnected to prevent warmup and cold!) and turn *slowly* the CO screw counterclockwise in / clockwise until you hear the injectors / nozzles spraying, then turn immediately at least a quart to a half turn clockwise counterclockwise until the injectors stop spraying.
3. Basic setup for the sensor plate (seems to be ok now), but you have to check it as Porsche is saying (0.1mm on a SC) The impact of the misconfigured sensor plate is huge, in both ways, and it affects the mixture over the whole speed band!
4. WUR control pressure - as seen, should be ok currently.
5. Did you checked the fuel pressure of the system? Is it in spec? Refer the Porsche manual. On an SC 4,8 up to 5,2bar.
6. There must no resistance in the way the plunger of the fuel distributor moves, especially when no pressure is applied (after sitting over night or being disconnected). If there's a reisitance even with no fuel pressure or disconnected, then it has to be overhauled!
7. Did you checked the fuel delivery of the fuel distributor between every cylinder? If one nozzle / injector is leaking you get more fuel than needed in that cylinder and that will ruin the results of lambda measurement, therefore you won't get a setup which is fitting from cold start up to WOT on high speeds. Pull the nozzles / injectors while connected to the fuel lines, and let them spray in measuring cups and compare them to each other. Max. alloowed difference is 5%! How do the injectory spray? If this is too poor, clean them in an ultrasonic bath or better replace them with new ones!
8. Are the numbers of WUR, fuel distributor, airflow sensor houising etc. matching to the car factory setup? if not, it will almost impossible to get a perfect setup!
9. Check all the vacuum lines on right connections! I experienced wrong connection of the vacuum lines to the distributor and throttle housing! This can also confuse as well the engine and the mechanic working on it because of unlogical behaviour...

Also interesting channel: Joe Engineer https://bit.ly/3soV4K3 he made several videos about CIS as well, Curt/Klassikats is also very very informative as mentioned already!

Regards, Thomas

['78 SC]

Sounds like you're nearly there, Mike. My '78 idles well (maybe a bit high) with the idle screw out 1.5 turns.

Did you repeat the smoke test with the everything assembled? That will check everything all the way to the manifold connections to the heads. (I missed the part about the fate of the air box - did you replace it or repair it? What about the pop-off valve?)

Just spitballing here, but an internal leak in the AAV, AAR or decel valve would affect idle. The good news is all of those use metered air (i.e. the supply line to each is downstream of the air flow sensor) so they wouldn't throw off the mixture.

You mentioned resistance when lifting the sensor plate. Is that with the fuel pump on? Without fuel pressure pressing down on the metering piston there should be no resistance. In my freshly rebuilt fuel distributor, the piston glides smoothly both directions under its own weight. With the fuel pump on, the metering plate should press down firmly. Be aware there will be residual pressure in the system after the fuel pump is turned off.

You can rough in the mixture by reaching into the air box with the filter removed and applying pressure to the sensor plate arm while the engine is warm and running. If it runs better when you apply upward pressure the mixture is lean - if it runs better with downward pressure it's rich. It doesn't take a lot of pressure and it won't feel like you're moving the arm, but it will be enough to alter the mixture. This procedure will actually get you pretty close to correct mixture.

[boyt911sc]

Pat,

Sorry to contradict about your post. The AAV and the decel valve were built and designed differently. Their functions are totally the opposite. You are one of the few people in this forum with a good understanding how and what to do about their CIS and that helps people.

But when you stated that the AAV works as a decel valve or vise versa, that is not correct. This is a Technical Forum, we could discuss and disagree but should not be taken personally. You could be right and I could be wrong, and only time will tell who is correct.

For starter, you could not use a AAV as a decel valve or vise versa. If someone did, that is not feasible or practical. Please prove me wrong and I won’t be offended. As a matter of fact, I would be thankful.

Tony

[boyt911sc]

Originally Posted by Schulisco

.........


2. Basic setup for the CO screw: Turn the CO screw completely in (clockwise), switch on fuel pump (sitting engine, WUR electrically disconnected to prevent warmup and cold!) and turn *slowly* the CO screw counterclockwise until you hear the injectors / nozzles spraying, then turn immediately half turn clockwise again. The injectors stops spraying.

Regards, Thomas

Thomas,

Maybe you meant the other way around? Could this be a simple case of a typo? When you completely turned in the fuel mixture screw inward, it would raise the FD plunger upward and cause a premature fuel delivery. I believe you it got this backward. Keep us posted. Thanks.

Tony

[Schulisco]

Originally Posted by boyt911sc

Thomas,

Maybe you meant the other way around? Could this be a simple case of a typo? When you completely turned in the fuel mixture screw inward, it would raise the FD plunger upward and cause a premature fuel delivery. I believe you it got this backward. Keep us posted. Thanks.

Tony

Tony,

you're absolutely right! My fault, sorry!

CW = richer mixture, CCW = leaner mixture.

For the basic setting of the fuel distributor (after correcting the height of the sensor plate), do not touch the sensor plate (lays in stop position), let the fuel pump run, lean the mixture as much as possible (sometime the injectors won't spray any more), then turn the scren CW until the injectory start spraying, then turn the back / CCW a 1/4 - 1/2 turn so that the injectors won't spray just like that.
Changes in this interval separate between rich and low mixture over the whole speed band! Only make 1/2 turn in maximum, as following the Porsche 911 Workshop manual!

If you later verify the CO - please notice: Follow also the Porsche manual while adjusting the CO mixture and disconnect the lambda sensor from the ECU if present, and disconnected vacuum pipes! And most important: Measuring the CO only in front of the catalyst, if present!

Regards, Thomas

[mikedsilva]

Originally Posted by '78 SC

Sounds like you're nearly there, Mike. My '78 idles well (maybe a bit high) with the idle screw out 1.5 turns.

Did you repeat the smoke test with the everything assembled? That will check everything all the way to the manifold connections to the heads. (I missed the part about the fate of the air box - did you replace it or repair it? What about the pop-off valve?)

Just spitballing here, but an internal leak in the AAV, AAR or decel valve would affect idle. The good news is all of those use metered air (i.e. the supply line to each is downstream of the air flow sensor) so they wouldn't throw off the mixture.

You mentioned resistance when lifting the sensor plate. Is that with the fuel pump on? Without fuel pressure pressing down on the metering piston there should be no resistance. In my freshly rebuilt fuel distributor, the piston glides smoothly both directions under its own weight. With the fuel pump on, the metering plate should press down firmly. Be aware there will be residual pressure in the system after the fuel pump is turned off.

You can rough in the mixture by reaching into the air box with the filter removed and applying pressure to the sensor plate arm while the engine is warm and running. If it runs better when you apply upward pressure the mixture is lean - if it runs better with downward pressure it's rich. It doesn't take a lot of pressure and it won't feel like you're moving the arm, but it will be enough to alter the mixture. This procedure will actually get you pretty close to correct mixture.

OK
I'm learning a lot as I go and do find these systems kinda fascinating. Problem is, I need the garage space back so I am not able to spend as much time on this as I would really like.



Auto air regulator - I removed it this morning to examine.. it does not open very far and we are currently around 30 deg C here... but the square notch is visible. I wondering if the unit was air tight... I didnt have a vac gauge but I did hook up my smoke machine to it. And smoke leaks easily from around the power plug. I had another old AAR and did the same test, and it also leaks from around the power plug. When running, could the engine also be sucking in a small amount of air from around the plug? I didn't have time to take apart and seal etc and I didnt want to break something, so at this stage, I have fitted it back to the motor.

Decel Valve - I had already plugged the vacuum line to the valve, but now I wondered if the valve itself was leaking air past the butterly. I removed the valve and used my smoke machine, and sure enough, while it does build pressure, a small amount of smoke does get through - both ways. I hooked up my mityvac brake bleeder to the lower port of the decel valve which is below the throttle plate, so I assume under vacuum, and while it did hold a decent vacuum, it still bled off little by little, every few seconds.
So I removed the decel valve, and fitted some fresh vac hose to the two ports on the top and bottom of the throttle body, and plugged with a couple of 10mm bolts. Thinking the threads would cause a leak, I smoke tested them both and when the clamps are tight enough, nothing gets past.

Then I fired up the fuel pump to start testing again... System pressure is in spec.

My cold control pressure is slightly low and not within spec. This would mean a slightly rich mixture at idle when cold and yes, I can confirm it is rich. AFR 10! What I did after it started, was to slightly push down on the sensor plate arm (lean the mixture) and the rpm picked up and the engine was much happier (afr went to 12 from memory) Of course, the WUR is starting to slowly heat up too so is starting to increase pressure (leaning the mix) but I was able to spend maybe 20 -30 secs experimenting and was certain that it would benefit from a slightly leaner cold mix (higher cold control pressure).

Now, I know I can mod the WUR and raise the pin somewhat, however, DOES THIS AFFECT WARM CONTROL PRESSURES TOO?

My warm control pressures are within spec (high side but still within spec) so I do not want to raise the warm pressures. Worst case, it means I will have a slightly rough idle when cold start. I would much rather everything be in spec when warm and sacrifice 2 minutes of inconvenience when cold.

When warmed up, I found that my idle was a little lower than yesterday.. I had it set to 950 ish, and today was just under 900. The only change I made, was to remove the decel valve and plug both ports. I guess there was a tiny leak?

With the engine speed adusted back up to 950rpm, (using my newly acquired digital timing light with tacho; great tool ) I can open the oil cap and the engine will not stall. It does however run horrible and drops to 650-700 rpm and the afr gauge goes VERY lean with all the extra air. I think it hit 17afr or leaner... It will idle at the low speeds, but it is the lean mixture that makes it rough.

My idle bleed screw will all but stall the motor. My guess is that my throttle plate is possibly a fraction too open but not by much. From memory, the idle bleed screw is open 1 full turn to maintain 950 rpm, but I will have to double check that, as I did not write it down.

So, at this stage, I feel I am fairly happy with how it is performing right now, depending on the advice that comes in the next couple of posts!

thank you in advance.

['78 SC]

Originally Posted by mikedsilva

...snip...

Now, I know I can mod the WUR and raise the pin somewhat, however, DOES THIS AFFECT WARM CONTROL PRESSURES TOO?

My warm control pressures are within spec (high side but still within spec) so I do not want to raise the warm pressures. Worst case, it means I will have a slightly rough idle when cold start. I would much rather everything be in spec when warm and sacrifice 2 minutes of inconvenience when cold.

When warmed up, I found that my idle was a little lower than yesterday.. I had it set to 950 ish, and today was just under 900. The only change I made, was to remove the decel valve and plug both ports. I guess there was a tiny leak?

With the engine speed adusted back up to 950rpm, (using my newly acquired digital timing light with tacho; great tool ) I can open the oil cap and the engine will not stall. It does however run horrible and drops to 650-700 rpm and the afr gauge goes VERY lean with all the extra air. I think it hit 17afr or leaner... It will idle at the low speeds, but it is the lean mixture that makes it rough.

My idle bleed screw will all but stall the motor. My guess is that my throttle plate is possibly a fraction too open but not by much. From memory, the idle bleed screw is open 1 full turn to maintain 950 rpm, but I will have to double check that, as I did not write it down.

So, at this stage, I feel I am fairly happy with how it is performing right now, depending on the advice that comes in the next couple of posts!

thank you in advance.

Adjusting the WUR cold pressure will not affect the warm pressure. When the WUR is fully warmed up, the bimetallic strip that provides the cold pressure compensation lifts free of the mechanism that controls the warm pressure and does not affect it.

I think the throttle plate should be fully closed. Maybe others here know that for sure.

In any event, if you have to open the idle control screw to get to 950 RPM, I think you've eliminated the air leaks. The behavior when removing the oil cap or closing the bleed screw confirm that you have no significant unmetered air.

Congratulations.

[mikedsilva]

Originally Posted by '78 SC

Congratulations.

I sure hope so!
I'm resisting the urge to mod the WUR.. just want to get motor back into the car.

Another issue I should note, is that out of the blue, I had minor "popping" in the exhaust and very slightly rough running. Looking at the Klassicats youtube videos, he shows a neat method of highlighting which cylinder is playing up, by cracking open the banjo bolt for each respective cylinders injector, on top of the fuel dist. I figured I would try it... got out the 12mm spanner and sure enough, crack the banjo and ask fuel would slowly leak out, the rpm would drop and the engine would stumble slightly. Good 'feedback' from the engine... when I got to cylinder 3, cracking the banjo resulted in nothing happening. Engine was unaffected AND no fuel came out.
This was a new symptom that had not presented itself before.... I swapped injectors between #4 & #3... but in hindsight that should have achieved nothing, as the fuel wasn't coming from the distributor.

When started the motor again, it was smooth, and I found that cracking each 12mm banjo resulted in the rpm dropping and fuel dribbling out... so perhaps it was just the re-start that dislodged something in the fuel dist.?

['78 SC]

Originally Posted by mikedsilva

I sure hope so!
I'm resisting the urge to mod the WUR.. just want to get motor back into the car.

Another issue I should note, is that out of the blue, I had minor "popping" in the exhaust and very slightly rough running. Looking at the Klassicats youtube videos, he shows a neat method of highlighting which cylinder is playing up, by cracking open the banjo bolt for each respective cylinders injector, on top of the fuel dist. I figured I would try it... got out the 12mm spanner and sure enough, crack the banjo and ask fuel would slowly leak out, the rpm would drop and the engine would stumble slightly. Good 'feedback' from the engine... when I got to cylinder 3, cracking the banjo resulted in nothing happening. Engine was unaffected AND no fuel came out.
This was a new symptom that had not presented itself before.... I swapped injectors between #4 & #3... but in hindsight that should have achieved nothing, as the fuel wasn't coming from the distributor.

When started the motor again, it was smooth, and I found that cracking each 12mm banjo resulted in the rpm dropping and fuel dribbling out... so perhaps it was just the re-start that dislodged something in the fuel dist.?

Clever technique. I never saw that used. Have to add that to the arsenal.

RE #3 fixing itself: "...hope springs eternal..."

You know the usual drill for checking fuel distributor operation - pull all the injectors and put them in small containers, then lift the air flow sensor arm and let the injectors spray for a few seconds. Check for equal volumes. Also, run each injector into a large enough container to view the spray pattern.

When my fuel distributor took a dump recently I checked the flow and got this:




This is about 10 seconds of flow without lifting the sensor arm, just running the fuel pump - so all the bottles should have been empty. Apparently the internal o-rings and maybe the diaphragm where seriously damaged such that fuel was breaking through on 4, 5 and 6. Of course, my wide band O2 sensor is on the left bank (1, 2 and 3).

[Schulisco]

@'78 SC
This looks awful. With no lifting the sensor plate the containers should look like #1 only!

Don't forget the check the injectors. Mostly they're also unusable because they differ too much on opnening pressure. If I'm correct the opening pressure should be around 2,6 - 3,6bar / 37-52psi.

If they differ too much and the fuel distributor also differs from each port will accumulate the differences in worst case. And the adjustment screws on the fuel distributor are only for fine tuning. You cannot balance the single ports if the differences are too large. I tried it also in endless fuel delivery tests to synchronize them as good as possible - but it will fail if one of the components isn't doing its job and you never get a proper running engine!
This is because the whole fuel delivery management is done by pressures only. If the pressures are not in balance and differ too much you won't ever get a proper adjustment and combustion in the engine, because that affects the rest of the system!
I would recommend to (let) overhaul the fuel distributor by somebody who's definitely firm with that. The best way is to refurbish it and after that getting a detaled measurement report of it to be sure that it works again as specified by Bosch.

Happy XMas!

Thomas

[targa80]

Originally Posted by boyt911sc

Pat,

Sorry to contradict about your post. The AAV and the decel valve were built and designed differently. Their functions are totally the opposite. You are one of the few people in this forum with a good understanding how and what to do about their CIS and that helps people.

But when you stated that the AAV works as a decel valve or vise versa, that is not correct. This is a Technical Forum, we could discuss and disagree but should not be taken personally. You could be right and I could be wrong, and only time will tell who is correct.

For starter, you could not use a AAV as a decel valve or vise versa. If someone did, that is not feasible or practical. Please prove me wrong and I won’t be offended. As a matter of fact, I would be thankful.

Tony

Tony,

I agree this is a tech forum and we should not take comments personally. In fact, I believe you and I have always been civil to each other and we agree on many subjects. We are both here to discuss, learn, debate and come to a common agreement on how these systems work and the best way to maintain them so our cars perform in the way they were designed.

Previously, you and I have talked about the AAV that was installed in my car, AAV model (-404). We both agreed that the functions for the AAV and the Decel valve are very different. I believe that I did not state that the “AAV and the Decel valve function the same”. What I did say in my post was “My model AAV has the open air/vacuum line port so my car looked like it had two Decel valves installed.” This was my though process until after talking with you and testing both devices. We agreed that I had the correct devices installed but they were incorrectly connected together at the vacuum ports as noted in the picture I posted.

My original issue was that I did not know that there are two models of the AAV. One model does not have a vacuum port nipple and is the most common model installed. The alternate model 404 that was installed in my car did have the nipple and without knowing the part number it visually looks the same as the Decel valve. To compound my original issue someone prior to my ownership had tied my Decel valve vacuum nipple to my AAV vacuum nipple. So initially to me it looked like I had two Decel valves installed that had the vacuum lines tied together.

If my posting is in error then I humbly apologize for any misstatements that may be confusing to any fellow pelican. My only goal is to add my knowledge along with others to help other pelican’s resolve their stated issues and provide a better understanding how these things work.

In my own case, it was individuals like you who contribute to this tech forum and the tech articles that helped me to learn and understand the functions of the CIS system and it’s ancillary components.

[SkiVT]

Can someone clarify: my Bentley seems to indicate you set the height of the plate without any fuel pressure. Since the plate rests on the height adjusting screw/stop, that made sense in my mind. However, the procedure posted in this thread several responses back says to apply fuel pressure, then set the height. Is this another Bentley error?




Thanks

[Schulisco]

@SkiVT Good point. I also red sth like that anywhere else, don't remember where.

My explanation: This is a more secure method to assure that the sensor plate really sits down on the adjust screw, This is why if you apply fuel pressure, it will (additionally) press down the sensor plate on the adjsutment screw / zero position. I guess this is in between of less than approx. 0,05inches / 1mm and probably might not make that much difference...but: I haven't checked this already, it's definitely worth a test...

Regards, Thomas

[boyt911sc]

Originally Posted by SkiVT

Can someone clarify: my Bentley seems to indicate you set the height of the plate without any fuel pressure. Since the plate rests on the height adjusting screw/stop, that made sense in my mind. However, the procedure posted in this thread several responses back says to apply fuel pressure, then set the height. Is this another Bentley error?




Thanks

Mike,

You need to confirm that the sensor plate arm pin is properly resting at the stop or spring when you perform the alignment. If there is some sort of binding by either the sensor plate or the lever arm, it’s not easy to know or identify it. But by pressing down the sensor plate, you could tell if the “pin” was in contact with the spring or not.

First, it is next to impossible to do a good sensor plate alignment with the motor installed. While it could be done, the alignment is difficult to verify or confirm unless you have an optical gadget to inspect the final setting.

However, if the motor or the air flow meter is out of the car, the work would be easy and simple. I have some pictures to share:

Cut 4 strips of bond paper and attach them using a scotch tape on the air funnel as shown in the picture below. Loosen the center bolt and let the sensor plate align it self. The 4 strips would help you get it very close to the center with no binding.



Visual inspection: With the aid of some lighting feature like a flashlight, you could easily perform a visual inspection of the previous alignment work. The uniformity of the air gap around the sensor plate and bottom of the funnel will dictate the accuracy of your alignment.



You could perform the sensor plate alignment with or without the FD supplying a control pressure as long as you gently press down the sensor plate to test its rest position. And don’t forget to confirm that the “rest pin” is in contact with the “stop spring”.

Tony

[SkiVT]

Thanks Thomas and Tony

[animal_uk]

Is it possible to adjust the angle of the sensor plate?
When I looked at mine although the front edge of the plate aligned with the narrowest point as in Tony's diagram above the far edge was above so the angle was the exact opposite of that shown in the diagram.

[Schulisco]

Originally Posted by animal_uk

Is it possible to adjust the angle of the sensor plate?
When I looked at mine although the front edge of the plate aligned with the narrowest point as in Tony's diagram above the far edge was above so the angle was the exact opposite of that shown in the diagram.

Afaik no. As shown in the Porsche / Bosch manual which I would refer to at first you can also see that they also recommend to use only the opposide of the funnel next to the fuel distributor as reference for the adjustment:





More important in conjunction to the correct sensor plate height is the "injection begin" (my personal definition) when the sensor plate is lifted by the sucked air of the engine. This has also a huge influence on starting & running culture, performance and fuel economy!



Finally you have to make a definitive CO mixture setting afterwards on a certified gas tester:



Thomas

[47silver]

on our 75.
10+ years ago, I cleaned this throttle body etc.
I was unsure of how to gauge the plate in the throttle body, but some one here posted the measurement requred between the throttle body and plate.
It is almost impossible to use a feeler gauge especially when the body is in the car.
8.5 x11 paper is too thick.
However TOP Cigarette rolling papers measure out to about that exact thickness, so I picked up some "cigarette" rolling papers.
They have a bit of adhesive so they can stick on the inside of the throat.
I lined the inside of the throat with them without over lapping the edges of the paper.
The papers centered the plate.
I set the plate down, raised the arm to fasten it and then tightened the screw.
that was over 10 years ago.
The motor starts, does not backfire, idles at 900 and runs to red line easily.

I cannot say that is the correct angle or way to do it but it worked perfectly on our 75.
the only thing i can think of is that the lever is already machined for the angle that is required.

[animal_uk]

The issue I was trying to understand was the 'bucking' at low revs, other than that it starts well idles at 900 and accelerates cleanly to the top of the red line.

The sensor plate does't touch the sides and is pretty central.
When I replaced the airbox I noticed that the sensor plate angle although slight was the opposite of that shown in the manual.
Looking at the post from Schulisco I think that at some stage the airflow sensor lever has been bent by 'accelerating the engine with the wrench in place'
The lever looked pretty substantial to me and would be pretty hard to bend.