Need CIS help... of course

[McGalliard]

The backstory:

The car is a US spec 1975 911 S that I purchased in January 2023. Not sure exactly what the real history of the car is, but it had probably gone relatively unused for some time recently (the latest reg sticker is 1989) but not unloved, per se. 62k miles on the odo and no reason to believe that's not the truth. Although I was assured it was started and driven around the block periodically, I'm not sure if that was true. Thermal reactors were removed prior to my ownership and the fan was upgraded from 5 to 11 blade.

Slowly, over the last two years, I've done the following:
New fuel tank
New rubber fuel lines from tank to tunnel, tunnel to pump, and then to accumulator
New Bosch fuel pump
New fuel accumulator
New fuel filter
Rebuilt fuel distributor
New rubber return lines from Y back to the tunnel and then tunnel to tank
New ignition wires
New spark plugs

Here are the symptoms:
-Hard cold start, but really no issues with warm start
-Once started, it hunts at idle a bit
-No smoke initially, but after a minute or two, whitish smoke that does not let up
-When warm and idling, the idle tends to be high, I think, around 1100+
(side note - my mechanic favors the smoke to be more over rich fuel than oil, but could be a combo)

Of course, everyone with knowledge on this forum says "PRESSURES, PRESSURES, PRESSURES".
I do have the pressure tester setup and over the last year or so it seems that every time I test the pressures, usually after a messed with some component, I've gotten different results and all are very confusing to me. Sometimes that adjustment was as minor as disconnecting and reconnecting a fuel line.

The latest pressure results are:
@ 13.5 deg C
-Cold control pressure: 0 bar
-System pressure: 1.8 bar
-Warm control pressure: 0 bar

The 0 bar is particularly confusing to me at this time. This has not always been the case. If I recall correctly, the first time I ever tested the pressure, which was before I was actually able to get her to run, I had reasonable control and system pressures that were a touch below spec. However, since I could not get ignition, I had to keep working and fixing and clearing... This was before the fuel distributor was rebuilt (professionally, although I did crack it open myself first).

I do have power in the plug to WUR, based on a noid test light. I had power to the plug at the CSV when I previously tested at some point in the past, based on a noid test light. The fuel pump output volumes were sufficient last I checked, but I suppose it wouldn't hurt to run it again.

Where do I start?? I'm hoping the 0 bar control pressures point to something straight forward, easy, and obvious.

Thanks in advance,
McG

[fanaudical]

Welcome to the forum - I've found lots of help here.

I've got a '75 Targa; I'm going to point you to my CIS troubleshooting thread from a few years back because it has some relevant info (I hope) for your car:

https://forums.pelicanparts.com/porsche-911-technical-forum/780952-sorry-yet-another-cis-troubleshooting-thread.html

I have some initial questions:

#1 - What are the part numbers on your WUR and fuel distributor? (This is necessary to know so we're all looking at the right graphs.)

#2 - What CIS components are installed on your engine aside from the WUR, fuel distributor/air meter, and cold start valve? Do you have a decel valve? Do you have the throttle valve? (I'm guessing decel valve and no throttle valve - some early '75's had the throttle valve.) EGR valve?

#3 - Sorry to ask, but are you sure you did your pressure tests correctly?

The reason I ask #3 is that I don't think it's possible for CIS to operate at 0 psig control pressure. The system pressure you state is way too low. Here is another link to Tony's write-up of how to perform the CIS pressure test:

https://forums.pelicanparts.com/porsche-911-technical-forum/888103-cis-fuel-pressure-test.html

Here's a YouTube video on the pressure test:



And another video that gets a bit more in-depth into CIS troubleshooting:



As far as where to start:

- Please report back on #1 & #2 above.

- Review the pressure test instructions and verify you did the test per instructions; if not, repeat the pressure tests and report back.

- Consider contacting user boyt911sc and ask him to evaluate your WUR. Tony is a good guy and offers rebuild/exchange services for these. Keep in mind that a rebuilt WUR will not help if your system pressure really is that low.

[boyt911sc]

My wife just arrived last night after 6 weeks of travel abroad and I’ve been very busy. Now, I have to get these stuff out where they belong.




McG,

Your CIS problem could be as simple as a bad fuel pump. You need to test and confirm that the FP is defective before replacing it. Some people are intimidated troubleshooting a CIS or lack the skill to do it. Taking a non-running car into a shop is EXPENSIVE particularly a CIS.

It would take me a few mins. to test and evaluate a WUR or FD and it is FREE. You just pay the shipping costs. Some of these WUR’s or FD’s that I received were GOOD and required no additional work.

So if your WUR or FD passed the tests, they are not the culprit/s to your nagging CIS problem/s. Look somewhere else, like a vacuum leak.

Tony

[McGalliard]

I have read so many of these forum threads and the CIS troubleshooting guides, etc. But have not come across a problem similar enough to mine that I can figure it out. Also, I'm not dumb but I am new to this and my brain tends to need hands on fixing to really gain a true understanding of what I'm doing and how this works.

I am pretty certain that I have done the pressure testing correctly, but I do have a tendency to make silly mistakes. E.g. high school calculus was a breeze, but I would inevitably not carry a 1 or I'd drop a negative sign somewhere rather frequently. One thing I am going to try is the inverting of the gauge limb of the testing setup to relieve potential air. Also, there's always the chance that my pressure setup is cheap garbage. But for now I'll assume it works. Finally, I have never mucked with the fuel pump relay terminals that everyone always mentions #87A and 30. But I'm not sure that this vintage needs that done. I just turn the key and run the pump. Please correct me if I am wrong.

I have been in touch with Tony on the side. But, I would rather know that the WUR likely needs rebuilding before headed down that route.

Part # for the WUR is 0 438 140 009
Part # for the FD is 0 438 100 006

As best I can tell, I think I have just the decel valve. Doesn't mean I'm not mistaken there either though.

[McGalliard]

Tony,

The new fuel pump went in as a part of cleaning up the fuel system before shooting old varnish through everything. When the original pump was removed it was gummed up/seized from old fuel. I can retest that this pump's output is sufficient if that's the consensus.

[PeteKz]

Your numbers don't make sense. With a SP of 1.8 and CP of 0, I doubt it would even run.

Running too rich causes blackish smoke, not white smoke. Burning oil causes white smoke--we tend to say it is "blue" because it has a slight bluish tint, but most people would call it white. Do you have your oil breather hoses and gas tank/charcoal canister hoses hooked up correctly? I'm thinking that you may be sucking oil into the intake some way.

Go back to basics:
- measure the SP, CCP and WCP again. Make sure you have the gauge hooked up correctly, and the valve in the correct position for each measurement. Post a picture of your gauge and how it is connected. Disconnect the wires to the WUR when you first measure CCP, then reconnect them and wait 5 minutes then test WCP.
- Rig up something to test your gauge on your tire pressure or compared to another gauge to make sure it is reading correctly.
- Measure the fuel delivery and see if that's within spec, and post your results.

[McGalliard]

I agree they don't make sense, which is why I'm coming for help. But trust me, it does run. I can upload a vid at some point. I have not yet taken a pic of the gauge connections, but the valve is certainly in the right position, downstream of the limb to the gauge, otherwise my pressures would be backwards and go to zero when the valve is closed instead of the other way around. I tested the gauge and it seems to be accurate. The brand is Betooll (from Amazon), which I've seen recommended here at least once. I purged the system of air, but it made little difference. There is no change in results with plugging or unplugging the WUR.

I have not messed with the oil breather hose since acquiring the car. Charcoal canister connection is fine.

Fuel delivery should be good. I measure 3L/min going into the fuel accumulator.

[boyt911sc]

Originally Posted by McGalliard

I have read so many of these forum threads and the CIS troubleshooting guides, etc. But have not come across a problem similar enough to mine that I can figure it out. Also, I'm not dumb but I am new to this and my brain tends to need hands on fixing to really gain a true understanding of what I'm doing and how this works.

I am pretty certain that I have done the pressure testing correctly, but I do have a tendency to make silly mistakes. E.g. high school calculus was a breeze, but I would inevitably not carry a 1 or I'd drop a negative sign somewhere rather frequently. One thing I am going to try is the inverting of the gauge limb of the testing setup to relieve potential air. Also, there's always the chance that my pressure setup is cheap garbage. But for now I'll assume it works. Finally, I have never mucked with the fuel pump relay terminals that everyone always mentions #87A and 30. But I'm not sure that this vintage needs that done. I just turn the key and run the pump. Please correct me if I am wrong.

I have been in touch with Tony on the side. But, I would rather know that the WUR likely needs rebuilding before headed down that route.

Part # for the WUR is 0 438 140 009
Part # for the FD is 0 438 100 006

As best I can tell, I think I have just the decel valve. Doesn't mean I'm not mistaken there either though.

McG,

We never had any communication regarding this subject. How did you get in touch with me? Please advise.

Tony


NOTE:
McG contacted me before under a different name last year.

[PeteKz]

The fuel pump delivery test is measured at the return line to the tank. You disconnect the rubber hose that goes from the left front corner of the engine bay to the lower firewall, and measure the flow without the engine running. The FP has to deliver that amount of fuel through the entire CIS and back to the tank.

Post the picture anyway. It might give us some hints at other stuff. I don't know how the SP would be as low as 1.8 bar, unless the pressure regulator valve on the fuel distributor was assembled incorrectly. If you verify the gauge is reading correctly, and SP really is 1.8 bar, then the next step after the FP delivery test will be to remove and inspect the pressure regulator valve, to make sure it was assembled and installed correctly in the FD at the last "rebuild."

Also post a pic of the WUR and its connections.

Once you get it stated, how does it drive?

BTW, air in the lines will not affect the pressure readings. No need to go through any acrobatics to bleed them.

[McGalliard]

I will try to get the fuel pump delivery test done at the level of the tank. I had done it in the past, but can repeat. It’s a little more work and difficult to do single handedly and temperatures have dropped again in NY, but I’ll try.

And for what it’s worth, my return lines are to the right of the supply lines. They return to the tank with a threaded connection on the lower right. The supply is the larger caliber hose clamped attachment that is left of center. It’s a Dansk replacement. I say all this because I’ve been known to do backwards things, so please question and fact check everything I write!

To add to the mystery, the car’s symptoms were not significantly changed after the FB rebuild. Pressures measured differently (worse, I think) but again they’ve been so all over the place that I couldn’t interpret or add weigh to that change.

Once the car is started, it hunts and rpms dip intermittently at idle. When still pretty cold, quick throttle with nearly stall it while slow throttle will rev more or less appropriately, though probably with a little lag. When warmer, the inverse response to quick throttle lessens.

Pictures will come when I get out of bed

-McG

[McGalliard]

Pressure gauge setup:

[McGalliard]

WUR: The plug is behind the vacuum line on the left. “Fuel out” is front right and “fuel in” is back right (with respect to the camera).

But I know you know all that already.

[ahh911]

Hi McG,

Your car runs, the correct fuel injectors open at 2.5 bar min. Your system pressure must be above that, at 1.8bar your injectors won't spray. The obvious thing to say is that your system pressure readings are incorrect for some reason. I overlook that and assume that your gauge and technique are correct, what would be the next possible scenario where your car runs but you measure low system pressure. A strange possibility is that the FD to wur pathway is blocked or chocked up, how it would run under that condition I have no idea.

Phil

[Johner]

It looks like you have a quick disconnect fitting between the pressure gauge line and the t fitting. I had a similar setup when I first did a pressure test and was getting results that didn't make sense. I found that the quick disconnect was causing the spurious results, and once I got rid of it the results were accurate.

John

[McGalliard]

My 3am cogitations concluded that I MUST have an issue at the FD (to the WUR). I would bet that the CCP and WCP pressures are not absolute 0, but so low as to not register. And yes, as ahh911 points out, the car runs so sufficient pressure must reach the injectors to open. This must be true. I too have thought that the FD to WUR path might be blocked or rather markedly narrowed, but it's not at the line between the two, so possibly in the FD itself? I don't really understand how fuel is diverted and directed in the FD, especially with respect to the WUR pathway. However, I would like to think that based on a recent rebuild of the FD and a lack of change of behavior before and after FD rebuild, that a problem inside the FD is unlikely, though not entirely ruled out.

Johner, I had already read your prior threads and posts about a janky pressure gauge and quick connects being an issue. I meditated on this yesterday too. At first glance, I do not see an easy way around them. At least not with the kit as it comes. So, I guess I will have to do some plumbing to be able to use the T and valve but remove the quick connect.

[Schulisco]

Please post a picture from the sensor plate resting position from underneath that we can see where it is sitting in the cone of the sensor plate housing.

Did you checked for tightness of the whole CIS with a smoke generator?

As others said already, you measurings of the CP makes absolutely no sense for a proper running CIS. The CP must be in the specified interval:



If your pressure readings were correct indeed, then there are some serious issues on it. The FD urges for the CP as it works as a counterweight to prevent the sensor plate moves too much corresponding to the sucked air. If the CP doesn't exist some time the rest of the CIS is tinted that much to cover this without solving the issues. This means you need a complete checkup of all CIS components to make sure that they are working as specified.

Here you find a troubleshooting guide for pre lambda CIS:
https://cis911primer.com/Troubleshooting%20Guide/Notebook%20Spiral.html

Also the whole 911primer website is quite informative.

The injectors are specified to open in an interval between 2.5-3.6bar! They're not bad if the opening pressure is higher than 2.5bar, as long as it is not higher than 3.6bar! You never have injectors opening at the same pressure. These injectors / jets / valves are pure mechanical with given tolerances.

Thomas

[ahh911]

McG,

System pressure can also be measured between the filter and distributor. Test line in series with valve open. Assuming the test equipment is okay, it should help narrow down the cause.

Phil

[McGalliard]

Originally Posted by ahh911

McG,

System pressure can also be measured between the filter and distributor. Test line in series with valve open. Assuming the test equipment is okay, it should help narrow down the cause.

Phil

I was thinking of where else I could test pressures… This will be one to try. However, I will probably first do the flow volume measurement at the tank from the return line. If that’s somewhere close to what it is pre-accumulator, then there shouldn’t be a significant drop after going through the new accumulator and the new fuel filter.

Unfortunately, it is currently -2 deg C, so I don’t think measuring pressures makes sense for now as we are literally “off the chart” for temperature.

-McG

[McGalliard]

Originally Posted by Schulisco

Did you checked for tightness of the whole CIS with a smoke generator?

Thomas

How does one do this? Where is the recommended access point? I don’t have a lot of vacuum components on this model. Maybe 2 lines?

Thanks

[ahh911]

Originally Posted by McGalliard

I was thinking of where else I could test pressures… This will be one to try. However, I will probably first do the flow volume measurement at the tank from the return line. If that’s somewhere close to what it is pre-accumulator, then there shouldn’t be a significant drop after going through the new accumulator and the new fuel filter.

Unfortunately, it is currently -2 deg C, so I don’t think measuring pressures makes sense for now as we are literally “off the chart” for temperature.

-McG

McG,

Return pressure is low pressure, the excess fuel that is sent back to the fuel tank. System pressure is found in the fuel distributor and the line that feeds it, i.e. the fuel filter to distributor line.

You can check system pressure at any temperature, even -2degC. Air leaks have no relation to system pressure as you probably know, best to stay focused for maximum progress and figure out why your system pressure readings are incorrect, be it test equipment or something else.

Phil