Basic CIS question - Page 2

MikeBogue · 07-26-2006, 07:53 AM

It is a solenoid actuated valve that should only inject when the starter is turning. Unforunately it can not be adjusted/rebuilt, but you can test to see if it is sticking. Just pull it out (located at the back of the engine) and put it in a glass jar while someone else turns the key. It should start and stop instantly with the starter turning over. If it does and does not leak when closed and it has a good spray pattern while the engine is turning over it is working correctly.

Paulporsche · 07-26-2006, 07:58 AM

Dan,

Sounds like your cold control pressure may be too high, giving you a too lean mixture @ startup. This is WUR. It's also possible your AAR is off a little, which is why your revs aren't high @ startup, although this may not be too much of an issue in So Cal. It's also possible your mixture is set just a little lean.

JCWhitney has a CIS .fuel pressure ga

Dan in Pasadena · Dan in Pasadena's Garage

Mike and Paul, Thanks to both of you. The most on-the-mark advice I've gotten so far. I went through another search in the last half hour and read that getting to the cold start valve is difficult as its at the back of the engine. If so, is the wiring to the valve long enough to be able to do the "pull-and-put-it-in-a-jar test, Mike? Have you done this?
As for the WUR - I remember reading something about tapping a plug in it(?). Guess I'd better got back to searching or this really will be a multipage hijack. I may post (yet another) CIS thread.

Mysterytrain · 07-26-2006, 10:13 AM

Yup..what Dan and Paul said. Couple of points to add here. Think of the WUR as a transitional device that is used between the cold start valve firing and the engine being at operating temperature. If the car fires right up and then stumbles, you most likely have the WUR set too lean. If it starts right up and then the rpm's hunt [high / low, over and over- like 17 year old sitting at a traffic light] you have the WUR set to rich. Adjustment requires tapping the pin in to make it rich and out to make it lean. I highly recommend that you make the WUR adjustable because it makes the process very accurate..a couple of PSI can make all the difference and whacking it with a hammer ain't my idea of fine tuning.
The WUR and the AAR work together during this transitional period. The AAR is providing the air and the WUR the fuel..hence, the warm up mixture. If one is not working properly then it will affect the operation of the other. Once the engine has reached operating temperature the AAR is out of the picture and the WUR is left to provide off idle enrichment via vacuum connection [at least thats how my SC works].
The AAR should be slightly open on a cold engine and full closed after a few minutes.

MikeBogue · 07-26-2006, 10:24 AM

I have not run this test on a Porsche, so I do not know as I bought a roller and have not installed the cold start valve yet.

Ron/Paul- I thought that the WUR/AAR worked of of a thermal proscess using a heating element to adjust the control pressure which should not make any significant adjustment over a 2-3 second time period (total length of time the engine sputters) unless there is a stick valve that loostens quickly.

Mysterytrain · 07-26-2006, 12:34 PM

I've become intimate with the CIS in my 78SC. So I want to be careful about what I say about the way CIS works on other cars but it is my understanding that the basics are pretty much the same. When you crank the starter the cold start valve shoots a healthy amount of fuel into the intake and the car fires up. Once the starter is released that fuel source is cut off and the engine relies on the WUR to feed it. My gut feeling is that the WUR must provide an almost equal amount of fuel to allow the transition to take place smoothly. On my car I found that the stumbling after the initial start up was from my WUR being set too lean. A whack of the plug corrected the problem. Unfortunately, the next morning I had the oscillating idle because I went a little too rich. This time when I pulled the WUR I made it adjustable and was really able to zero in on the control pressure.
Back to what you asked..yes, the WUR and the AAR are temperature controlled devices but if you notice the vacuum connections on a 78SC there is a thermotime valve that prevents vacuum from being applied to the WUR for the first few seconds of start up. This helps keep the control pressure on the rich side for a few more seconds. I'm quessing that the factory hung this thing on there for a reason. Once, the engine has stablized and the thermo valve opens, the vacuum leans the WUR.

Dan in Pasadena · Dan in Pasadena's Garage

Ron, Thanks for the info. I suppose I DO need the CIS test setup and just "whacking" that plug in the WUR blindly would be ill advised.

Still, if I test it or not and decide to try the "whacking" method (you realize what a non-Porschephile stumbling into this thread would think?!)how do you measure the depth of change to the plug you are hitting? A tire tread depth guage seems like it would work.

Guess I'd better do a search for the thread on making the WUR adjustable and try those disconnected cold start valve, and in-the-bottle tests.

Mysterytrain · 07-27-2006, 05:10 AM

If you look at the cross section of the WUR you will see the plug, the arm, etc and the diaphram that is actually controlling the pressure. Although I enjoy the humor in the image of fine tuning a 911 with a hammer and a punch, I've come to realize that 'WHACKING THE PLUG' is really too coarse an adjustment. Its too hit or miss even with gauges. Once I made the WUR adjustable I set it rich, with the plug much lower then it should be. I attached the gauges and slowly tightened the nut to pull the plug up and lean it. I was amazed how sensitive this adjustment was. I also began thinking in terms of PSI rather then BAR. A couple of PSI makes a big difference.

Hladun · 07-27-2006, 08:38 AM

The exchange between Mysterytrain and Dan in Pasadena was briefly entertaining but it’s a classic example of what I call "1/4 turn tuning". Guys, you've bought a Porsche, either get someone who knows to fix it or get the right tools to do it yourself. For a CIS the tools are the pressure tester and an exhaust gas analyzer (A/F meter). Sadly the CIS has gotten an undeserved reputation because it can relatively easily adjusted by someone who doesn't know to a state where it doesn't work.

MikeR90S · 07-27-2006, 10:06 AM

As Jim Sims said, early 911 CIS is as originally shown and includes a throttle actuated control pressure valve. This enrichens the mixture (drops the control pressure) at full throttle. Later CIS accomplished the same with a vacuum controlled WUR.

Mysterytrain · 07-27-2006, 11:44 AM

Hladun..I'm not sure I understand what you mean by entertaining. I'm not recommending that anyone adjust the WUR without a set of gauges. If anything I thought I was offering up 'my' experience with 'my' system and the interaction of the WUR and AAR.

Dan in Pasadena · Dan in Pasadena's Garage

Ron,
Started to write a response to Hladun's advice and "tone", I decided better. Thanks for the discussion and friendly advice. THAT kind of advice is sincerely appreciated.