Troubleshooting my '74s CIS system
 

Hi all,
First post for me since acquiring my first Porsche - a 1974 base model coupe. The car runs but doesn't run nearly as well as I think it should. Runs rough when cold and has an unsteady idle that is difficult to get under about 1300 rpm. If I try to turn down the idle below that, it gets pretty unsteady. Off-idle running is actually pretty decent, though I have no other 911 experience to go by. Anyway, I decided to go through the CIS system to make sure pressures are in-spec, everything tests out within normal ranges and there are no vacuum leaks. Here is what I found so far:

- System pressure is 4.2 Bar - below spec. I have not yet adjusted the pressure regulator with shims to raise it into spec.
-My WUR is not stock - see pics. It does function, meaning it warms up and control pressure changes, but since I don't know what the pressure over time chart should be, I have no idea if its in spec.
- Flow rates were inconsistent from injector to injector. I moved the injectors with lower flow to the FD ports that had higher flow. The problem did not move with the injectors, so the variation is within the FD. The difference between the higher and lower flow rates is about 6%.
- The control pressure regulator for throttle position is completely disconnected. The fuel line from the FD to the valve is disconnected. Kind of surprised the car drives as well as it does with the valve disconnected.

I have not tested for vacuum leaks with my smoke machine yet. That's next. Here are my questions:

1. Does anyone know what my WUR is from and do they have specs for it? There is no model number stamped into the WUR after the Bosch part number. It's blank.
2. Is the difference in FD port pressures significant enough to warrant having the FD sent in for servicing?
3. Does anyone know why my control pressure regulator for throttle position would be disconnected? I suspect it stopped working and was disconnected because they are NLA. Anyone else do this with their '74-75? If the car would run fine without it, should I be concerned?

Any help or insights would be appreciated.

Thanks,
Brian

http://forums.pelicanparts.com/uploa...1711213370.jpg
http://forums.pelicanparts.com/uploa...1711213370.jpg

CIS Troubleshooting…………
 

Brian,

Could you post another picture of the WUR showing the Bosch ID # (0 438 140 XYZ). The last 3 digits identify your WUR. The numbers are blocked by the wire in your picture. Thanks.

Tony

Hi Tony,
There are no numbers. It's blank. I know there is supposed to be a 3-digit model number after the Bosch part number but this WUR doesn't have one.

Brian

Brian - that label (top pic) is a part number.
what Tony is asking is the pic of your WUR, the three additions numbers are hand stamped and hidden under that green wire insulator. It might be faint or dirty but there’s 3 more numbers somewhere after the 438-140- _ _ _

Here’s an example of how the number it’s stamped ….


http://forums.pelicanparts.com/uploa...1711220757.jpg

The TPR has 3 positions. Idle setting, slightly lean at mid throttle position, and richer wide open throttle. No way to tell why the TPR is disconnected without connecting it and testing control pressures. They eliminated the TPR on later models and changed to a vacuum WUR.
System pressure is a bit low. Might need shimming, or could be a worn O-ring on the pressure regulating piston.
Yours looks like it could be an 0 438 140 129.
http://forums.pelicanparts.com/uploa...1711220674.jpg

If you have the original 0 438 100 004 fuel distributor, there is no way to adjust individual fuel flow. If flow difference doesn't follow when you moved injectors it is probably inside the fuel distributor.
Flow difference may be from a clogged tiny filter screen, the little red thing in the O ring to the left in the picture. They are at the outlet of the 6 fuel lines to the injectors.
http://forums.pelicanparts.com/uploa...1711222635.jpg
Before you spend the money to send it out for repair you could try and clean it yourself. There are a couple of companies for around $100 that make rebuild kits for the fuel distributors. They have the steel plate and O rings needed to refresh the internals. I found with a little care it is not too difficult to replace all the O rings. Mostly what I find inside is not rust, but the reddish residue from gas.
http://forums.pelicanparts.com/uploa...1711223547.jpg

I checked the WUR really closely with a flashlight, looking for a faint stamping on there. I know one SHOULD be there but I don't see one. I'll double-check in the morning to make sure I didn't miss it.

So I'm guessing a 6% difference in fuel flow is significant enough to warrant taking the FD apart and cleaning it? Also, does anyone have a pic of the fuel fittings on the top of the FD where the WUR fuel line and the fuel line for the TPR get their fuel from? I think the fitting on there is not original so I need to know what goes there before I can re-attach the TPR to test control pressure at idle, part-throttle and full throttle.

thanks,
Brian

This was in bad shape when I bought it for spare parts. Unfortunately the throttle body was shot but I got the rest back into shape with quite a bit of cleaning.
On the left you can see the TPR connection is first on the top of the fuel distributor, then the stem that connects to the WUR.
You can get a pack of copper sealing washers and remove the bolts on the fuel distributor injector lines and see what shape the small red filters are in. I find it interesting that the filters are not mentioned in the parts catalog or service manual. You can also try testing the fuel flow with the injectors removed to see if fuel flow evens out.
Here is a good thread on cleaning fuel distributors.
http://forums.pelicanparts.com/porsche-911-technical-forum/272657-cis-fuel-distributer-cleanout-w-pics.html

http://forums.pelicanparts.com/uploa...1711283701.jpg

This is the definitive thread on early CIS, best on the Web

https://www.ddk-online.com/phpBB2/viewtopic.php?t=51455&start=390

Of course the entire thread is great too!

Here's a link to testing the K Jetronic. Pages 23-25 show testing injectors.
https://members.rennlist.com/vilhuer/K%20Jetronic%20Workshop%20Manual.pdf

Here is a clearer pic of my WUR. There is NO model number after the Bosch part number. Now what?

A couple more questions - if I want to replace my fuel line from the FD to the throttle valve regulator, how do you get these polyamide lines off and back on again at the throttle valve side? There is no fitting or clamp. Are these lines supposed to be heated to get them off or on? I'm not used to working with lines like these.

Does anyone know where I can get that banjo fitting on the top of the FD that supplies fuel to both the WUR and the throttle valve regulator? I'll need that to reconnect mine.

Thanks,
Brian

http://forums.pelicanparts.com/uploa...1711327172.jpg

Hi Brian, Others know more than me on the other issues.

Why do you need to remove the line? It is best to leave them alone unless truly necessary. There is no way to remove the polyamid line other than damaging it at the fitting with a soldering iron and pulling it off. You can then trim it to an undamaged spot for reinstallation if it is still long enough. These lines are difficult to install without a proper tool to hold the line while you press the fitting onto it. There are some threads here on methods.

Len Cummings (BoxsterGT here) here may have replacement line material, if you need it. These guys may also be helpful: https://www.dssales.net/CIS.htm

For CIS Systems the best advice is to be sure everything outside of the CIS System is spot on before messing with the CIS parts. This means a complete tune-up (points, rotor, cap, air filter, fuel filter, dwell, timing, and valve adjustment). CIS is very robust once it is right.

Hi Harry,
For some reason, the throttle valve regulator is disconnected at the FD. The line is just hanging there. I assumed a bunch of dirt got in the fuel line as a result so I was thinking of changing the line. I suppose I could just clean the fitting at the banjo bolt end and test it out though. Any dirt in the line would be cycled back to the fuel tank anyway rather than the FD.

Brian

Preliminary Investigation………
 

Brian,

There could be several reasons why the TPR was removed. It could be defective and not repairable. Same also with the OEM WUR-001. Why do you need a TPR? Deleting the TPR from your CIS and installing a good working WUR would be an upgrade.

First, you need to test and evaluate the TPR. Do not remove the polyamide fuel line from the TPR unless you have experience working with this type of fuel lines. If the line is not leaking, leave it alone. These are some of the “control TPR” I use for my tests.

http://forums.pelicanparts.com/uploa...1711373967.jpg

Second, test and evaluate the control fuel pressures (cold and warm) for your mysterious WUR. Check the heater resistance (Ohms). Keep us posted.

Tony

Thanks Tony. I did test the WUR already, but my system pressure was low (4.2 Bar) so I'm not sure the readings are relevant. I need to shim the FD to get system pressure in spec and then re-check the WUR. The one thing I can tell you is that the heating element is working and control pressure changes over time when the element has 12V applied to it. The problem is, without knowing the model number of the WUR, I don't know what "in spec" control pressure is for this WUR over say, a 10 minute test period. Without that, it's hard to say if its working properly or not.

Brian

Tony, to answer your question about why I need a TPR - I just assumed that if Bosch/Porsche designed it as part of the CIS system, it was needed. From what I understand, it leans the mixture at part-throttle and richens it at full-throttle by modifying control pressure. So, if it isn't working, doesn't that mean I'm running too rich at part-throttle and too lean at full throttle? I just know these CIS parts are designed to work as a unit, so I wanted to get everything connected properly and then get pressures (system and control) in spec to see how the engine runs at that point. I still have to do a smoke test for vacuum leaks as well. That's on the to-do list.

Brian

Knowledgeable People……….
 

Brian,

You don’t need to know the spec of this mysterious WUR. I will tell you why later. First, set the system pressure to 70~72 psi. You will need an assortment of shims to get your target system pressure. After you successfully set the SP to 70~72 psi., time to test the control pressures (cold and warm).

After you have set the SP (system pressure) of your FD, then time to test your WUR. The control pressure is a function of temperature so you need to know the approximate ambient temperature in the garage or work area.

Test run the FP (fuel pump) with the gauge hook up. To measure the CCP (cold control pressure), disconnect the electrical connections to the WUR before you run the FP. This is very important. The pressure reading on the gauge (power to WUR disconnected) is CCP.

To measure the WCP, you need to connect the power to WUR. You also need to install the correct plug to the WUR. There is a transition time between CCP to WCP base from the heater resistance and calibration. So work experience would be very helpful if you have done this type of work in the past.

This is how you measure the WCP:
1). Disconnect power to WUR.
2). Engine cold, test run FP. The initial reading is CCP.
3). Using a timer, measure at 1 minute intervals after connecting power to WUR.
EXAMPLE:
0…………..CCP
1 min.
2 min.
3 min.
Etc…………WCP (pressure reading max. out and steady)
Note:
Measure the heater resistance (Ohms) when engine/WUR is @ RT.

If you have any question, just ask. It might look complicated but it is easy and simple. Keep us posted. Thanks.

Tony

Tony, you commented "There could be several reasons why the TPR was removed. It could be defective and not repairable. Same also with the OEM WUR-001. Why do you need a TPR? Deleting the TPR from your CIS and installing a good working WUR would be an upgrade."
Now, if your suggesting changing to a later vacuum WUR, would a later throttle body from a '76-77 be needed for the additional vacuum port?

Brian,
To give you an idea of what to expect. The O ring you should replace along with the shims are shown in my photo.

http://forums.pelicanparts.com/uploa...1711385072.jpg

http://forums.pelicanparts.com/uploa...1711384541.jpg

Ed,

If you are into concourse restoration, keep everything as original. The problem with the early CIS (73.5~ ‘74) with TPR and FD-004, they are not users friendly. The polyamide fuel lines do not use fuel like fittings unlike the later CIS. The TPR’s and WUR-001/-008 are all practically not rebuildable items. And the factory later replaced them with better designed components.

The ‘76-‘77 CIS are much better and improved than the early CIS. And the SC’s are much better than the mid-year CIS. The different CIS components are inter-changeable if you know how re-calibrate them.

Tony