2.7 will not run well after CIS rebuild

[Ginger77]

It's spring so I'm reaching out for help with my CIS rebuild. I literally spent too much time fiddling, reading about all the vital topics that have accumulated on Pelican over the years. I have learned so much but I'm getting demotivated because I'm struggling to get my engine to run. Also my 911 needs to go to biannual inspection and I've already missed the due date.

CIS is rebuild: I renewed all gaskets, rubber o-rings, injector sleeves, intake rubbers, rubber crosspipe behind the airbox. I purchased an aluminium airbox from a Pelicanite to make sure I'd not have air leaks.
The FD is rebuilt with a Missing Parts rebuild kit and checks out with 4.7 bar SP and I tested the flow. I don't currently have the data at hand but the flow matched the spec.
I made my WUR adjustable using the invaluable info here on the forum. I also purchased new WUR springs and a permanent pressure gauge kit from a german Mercedes parts store to control and monitor my pressures. The heating element gives a nice 26 Ohms resistance. I used this great step-by-step Mercedes Benz manual to test and calibrate my WUR. The manual goes through all the steps where I ran the WUR without the sombrero too.

For reference. The control pressures are as follows for my 1977 2.7 033 WUR.
CCP 1 bar (13 degrees C = 55F) 15 PSI
WCP 2.9 bar (takes about 6 minutes) 42 PSI
WCP 3.3 bar with vacuum 48 PSI
These are according to spec given the workshop info I'm using.

I installed an AEM AFR gauge to monitor mixture.
Out of precaution I renewed the fuel pump as the old Bosch had an irregular whine during control pressure testing. New pump is a Pierburg item and I put in a new Mahle KL-25 filter.
The vacuum lines are correct where the bottom of the 033 WUR goes to atmosphere above the throttle plate. The top of the WUR goes to the side of the thermal valve and the center of the thermo valve tees the distributor and throttle housing below the plate.



When I checked the AAR it closed in 5 minutes.
I purchased new injectors because some of the old ones dripped.
I set mixture to where the injectors spray and then backed off a half turn.

The engine starts up and revs up to 1800rpm with an AFR of high 11s. Then comes down as you'd expect from the AAR closing and control pressure rising. But after a few minutes the engine runs super rich. AFR is in the 9. My eyes get watery and my 911 is parked underground. Unfortunately, I've set of the CO alarm twice already.

https://youtu.be/CgmPFwfwgSw

The sensor plate is vibrating like crazy. And the needle in the little control gauge is playing pinball. What is happening here?

My assumption was that perhaps the CSV is not shutting down since backing off the mixture has no effect at this point. This would make the CSV run super rich. Or something is up with the vacuum such as the signal to the thermo valve. Does the connector go a specific way? It seems that when the TTS reaches a temperature something is up with either vacuum because the WUR gauge is all over the place. Or there is way too much fuel?
Since the CSV is controlled by the Thermo time switch. I took the TTS out. The resistance checked out low. The Bosch manual states the following values and mine are in bold:

Below 104F
G-Ground 30-40 24
W-Ground 0 0
G-W 30-40 24

Above 122F
G-Ground 55-85 60
W-Ground 0 98
G-W 55-85 40

I bit the bullet and purchased a new item which doesn't give any resistance values on my multimeter.



I have a spare CSV that I intend to test too. But first I want to see what the new TTS does. Although I don't want to void warranty on a €200 item. However, it came in a Porsche box stating the quality has been checked.

My car is not parked at my house and I won't have time to go out again until tomorrow afternoon. But I'd very much appreciate any help here. I feel that I've tested the components and probably renewed more items than I would have needed (in retrospect) but I must be in at around €1500 of parts by now and I can't figure out why the engine won't run well.

Much appreciated.

[runner4fun]

No expert here, but I had to replace my CIS fuel distributor with a rebuilt unit.

[Walter_Middie]

Check that your CSV only gets power when the starter motor is engaged. The plugs for the WUR and CSV are the same, and can be mixed up. The WUR gets power all the time. That may be the easier check - to ensure the WUR is not getting power only when the starter is engaged.

[fanaudical]

Have you attempted to set the idle mixture and speed once the car is up to temperature? I think a 2% CO content is around 13.8 AFR. Also, have you verified position of the plate in the airflow path?

[boyt911sc]

Originally Posted by Walter_Middie

Check that your CSV only gets power when the starter motor is engaged. The plugs for the WUR and CSV are the same, and can be mixed up. The WUR gets power all the time. That may be the easier check - to ensure the WUR is not getting power only when the starter is engaged.

Walter,

Physically impossible for WUR’s plug to get mixed up with the CSV’s plug even if you try it. Maybe you meant CSV and AFM sensor switch getting mixed up. Keep us posted.

Tony

[47silver]

Did you have to remove the air flow plate? If so how did you calibrate it? I used cigarette rolling papers and set them around the plate. The papers are very close to the specs. Worked for me and that was 10? Years ago

[Walter_Middie]

Tony,

The switch between WUR and CSV happened to me. It is easy to do. I had to tow my car to John Walkers where he diagnosed the problem in 30 seconds - as he was familiar with this issue. The electrical connectors in 1975 were exactly the same for both of these.

[Dave Kost]

The proper way to set the initial mixture per Larry Fletcher CIS Flowtech. He includes this procedure is the box with the rebuilt fuel distributor.

After assembly of the fuel system, run the fuel pump and depress the air flow sensor plate for a couple of seconds to bleed air out of the fuel distributor. Remove one injector line from the top of the fuel distributor, and while looking into the injector port in the top of the fuel distributor turn the mixture adjustment screw clockwise until the port just starts to fill with fuel then turn the mixture screw 1/2 turn counter clockwise. Reinstall the injector line, start the engine and adjust mixture when it reaches operating temperature. This is the Bosch recommended procedure for initial mixture setting and adjustment.

Then set the CO and rpm to spec.

Let us know how this works.

[boyt911sc]

Originally Posted by Walter_Middie

Tony,

The switch between WUR and CSV happened to me. It is easy to do. I had to tow my car to John Walkers where he diagnosed the problem in 30 seconds - as he was familiar with this issue. The electrical connectors in 1975 were exactly the same for both of these.

Walter,

The problem with accidental switching or mixed-up of the electrical plugs happen only between CSV & AFS (airflow sensor) switch NOT with WUR. For the sake of discussion, go to your car and take a look. The WUR’s plug won’t reach either of the CSV nor the AFS switch. But CSV’s and AFSS’s plugs often get involved with this blunder. You might have misunderstood JW.

Tony

[Walter_Middie]

Tony - do I have an AFS? The fuel pump runs with the key on - no waiting until it starts to crank.

It would make sense for Porsche to Murphy proof these at some point, as I can't be the only one to make this mistake.

My car is in the body shop for some minor rust repair right now so I can't run out and check, but I remember the wiring harness was routed incorrectly to make the wrong connection possible - the wires didn't reach easily - as you said.

[boyt911sc]

Originally Posted by Walter_Middie

Tony - do I have an AFS? The fuel pump runs with the key on - no waiting until it starts to crank.

It would make sense for Porsche to Murphy proof these at some point, as I can't be the only one to make this mistake.

My car is in the body shop for some minor rust repair right now so I can't run out and check, but I remember the wiring harness was routed incorrectly to make the wrong connection possible - the wires didn't reach easily - as you said.

Walter,

Your ‘75 does not have an air flow sensor switch. It was introduced in 1976 models up to the last SC (1983). We are discussing about Ginger77. The wiring harness for this particular CIS model has the CSV & AFM plugs tucked close each other. While the WUR plug is about a foot away from these 2 plugs.

It is physically improbable to get the WUR plug hooked up to either CSV or AFM even if you intentionally want to do it. The ‘77 engine wire harness has four (4) similar plugs namely:

• WUR (Gray)
• AAR (Black)
• CSV (Blue)
• AFS (Green)

The blue and green plugs are the ones commonly get mixed up because they are tucked too close to each other in the engine wire harness. The two (2) plugs (gray & black) are too far away from the rear.

Are you even familiar how the engine wire harness is laid on top of the Fiberglas shroud? With the 14-pin connected, the WUR (gray) plug won’t reach the CSV.

Tony

[Dave Kost]

Originally Posted by Dave Kost

The proper way to set the initial mixture per Larry Fletcher CIS Flowtech. He includes this procedure is the box with the rebuilt fuel distributor.

After assembly of the fuel system, run the fuel pump and depress the air flow sensor plate for a couple of seconds to bleed air out of the fuel distributor. Remove one injector line from the top of the fuel distributor, and while looking into the injector port in the top of the fuel distributor turn the mixture adjustment screw clockwise until the port just starts to fill with fuel then turn the mixture screw 1/2 turn counter clockwise. Reinstall the injector line, start the engine and adjust mixture when it reaches operating temperature. This is the Bosch recommended procedure for initial mixture setting and adjustment.

Then set the CO and rpm to spec.

Let us know how this works.

The above is the initial settings to get the car running. What this does is it gets the plunger of the FD (fuel) and the AFM plate (air) in position so the car will start.You didn't do it right. (See above) Then make your adjustments to get the CO and RPM to your engine specification.

Did you try setting the CO and RPM by adjusting the 3 mm allen screw and the air by pass screw on the throttle body? (You don't mention it.) You do this at warm idle.

Less fuel - 3mm screw counter clockwise
Less air - air by pass screw clockwise

You should be able to bring the engine rpm down by closing the thumb screw.

You probably know this but you didn't mention doing it.

Why not a Bosch pump? 9 AFR is just off the charts rich!

[fanaudical]

I think the procedure that Giner77 lists does match the factory procedure. Here's a link to a post with pics of the factory procedure:

CIS Starting Point After Fixing Leaky System

Regarding bouncing sensor plate and buzzy gauges - Does it run better if you disconnect your test gauge?

Bouncing air flow plate

Another link that may be useful:

Airflow meter plate moves with FP

[Ginger77]

Thanks for the replies. Just to provide some answers. I did not remove or alter the position of the metering plate in the process. And this has not occurred before.

Like Tony says, the connections behind the air filter housing have specific colours and I'm afraid the problem is not as simple as mixing them up. Also there's no way the WUR can reach there. I've spent enough time around the assembly to know where all connectors go.

Why a Pierburg pump? Because there really good.



Also, I set mixture according to this manual. But it's hardly possible to adjust mixture when the metering plate is going crazy. I know you're supposed to tune mixture and idle speed with a warm engine. But in the current state there's no way my engine can reach operating temperature. Also the RPMs in the clip are around 800. Very low, very rich.

I noticed that the vibrating metering plate almost exclusively happens to 930 turbo engines. Why would that be? As for my fuel head: All rubbers and o-rings have been renewed in my FD. Including the pressure regulator parts:



I saw a mention of people who had said it was due to their fuel pressure gauges. But then elsewhere I saw them mentioning is was due to something in the end.

Most CIS topics are like a quest where I would be send off to measure this or that and then come back to exclude items or pinpoint the problem. What could I check at this point?

I can verify the position of the metering plate according to this manual:


I can take the Mercedes fuel pressure gauge out of the equation and hook up my CIS gauges again.

I can unbolt my FD and see if the plunger still moves freely and has no scoring.

Anything else? I wish I could swap out the FD but I don't have a second.
Should I still swap out the TTS or would I be better off returning the $200 item?

[Ginger77]

I accidentally posted the downdraft paragraph of the metering plate height adjustment. Here's the correct updraft:



But my '77 has a screw for adjustment and not a clip.

[Dave Kost]

Thanks for the up date and clarity.

I would lean out the 3 mm mixture screw a full turn and start it up again. Also, one of the jobs of the fuel accumulator is to dampen the fuel pump pulses so, I would check it too.

If it were me, I would put the old fuel pump back in.

Why did you decide to rebuild the CIS system? Any particular reason?

[Ginger77]

I had intake leaks. The car would keep on coasting when I'd approach a red light.

I'm glad I did when I started. Some injector sleeves had disintegrated.

[pmax]

Originally Posted by Ginger77

It's spring so I'm reaching out for help with my CIS rebuild. I literally spent too much time fiddling, reading about all the vital topics that have accumulated on Pelican over the years. I have learned so much but I'm getting demotivated because I'm struggling to get my engine to run. Also my 911 needs to go to biannual inspection and I've already missed the due date.

Hi,
In your 77, there's an CIS elf called the thermovalve (Not the TTS) which can muck with your FP.

I haven't seen you mention checking it yet. Search for these threads.
Here's a description from the CIS Primer, if you haven't already seen it, #4 in the diagram.

https://jimsbasementworkshop.com/CIS/pages/descr_midyear.html


BTW I doubt it's your CSV. The other little CIS elf is that decel valve #8 which should not be doing anything except in decel conditions which I assume you are not testing under, but if misbehaving could muck with your car running well. So, I would consider eliminating it from the puzzle by taking it out, just for testing purposes, although many do it permanently since it is apparently for emissions and can hang up your throttle on lifting. Porsche got rid of #4 in later versions of the CIS.

Good luck !

[Ginger77]

Before the rebuild I did not have a thermo valve. I sourced an NOS item so I'm thinking it's not malfunctioning. But please let me know how I can test the item.
Also the acorn decal valve holds a half bar vacuum when I use my Mityvac. This indicates it functions as it should. Correct?
Furthermore, I'm also aware that the diagram above is incorrect for my 033 because the WUR connections are swapped. Vacuum (top) and atmosphere (bottom) as the note at the bottom mentions. And the top of the decel valve goes to the back of the throttle body. No tee here. But there's a tee from the distributor and the front vacuum of the TB going to the center connection of the TV. I'm referring to the very first diagram I posted at the top of the page.

I first want to focus on the FD. I'll unbolt it from the housing and see if the plunger is sticking. And I'll pull the pressure regulator. To see if that assembly moves freely.

[pmax]

Originally Posted by Ginger77

I made my WUR adjustable using the invaluable info here on the forum. I also purchased new WUR springs and a permanent pressure gauge kit from a german Mercedes parts store to control and monitor my pressures.
...
For reference. The control pressures are as follows for my 1977 2.7 033 WUR.
CCP 1 bar (13 degrees C = 55F) 15 PSI
WCP 2.9 bar (takes about 6 minutes) 42 PSI
WCP 3.3 bar with vacuum 48 PSI
These are according to spec given the workshop info I'm using.

Did you read the link someone posted previously ? It said the gauge kit could be a cause of the fluttering, and you have one installed.

Your CP numbers above might be right, looks OK to me, but those assume the vacuum is in spec. All I'm saying is #4 plays a main role there. So, the PO deleted the unit. I can understand why since that reduces the number of variables, elves I call them and complexity which is the opposite of what you're embarking on.