CIS Cold Starting Problem

[GregS]

Hi. About a month ago, we took our '73T up into the mountains, at an altitude of about 9000 feet. We live at about 5000 feet here near Albuquerque. Prior to the trip the car had been starting without any trouble at all. The first day we tried to start it at the high altitude, it took over 20 minutes to get it going, and the problem continued until we got home. I took it into our mechanic, who replaced the thermo-time switch. That helped, but it is still not right, taking at least 5 minutes to get started when its cold. After the car has been started, and run during the day, it generallly starts OK, but its still not right. Last year we replace the warm-up regulator. I'd sure appreciate any thoughts and ideas. Thanks for your help.

[stlrj]

It sounds like a problem with your cold start valve.

What happens if you briefly push up on the sensor plate with the ignition on and then try to start it? If it starts, then you'll have to find out why your cold start valve isn't working.

Joe

[Sunroof]

I have the same car (73.5 T) with CIS and have been struggling with cold start for along time. First, I was advised that the very first CIS (73.5T) does not have a thermo time switch! I went to my very reputable mechanic who showed me where it would go, but no dice. You have to tell me your secret....................please!

I pop, putter, spit and groan in the morning on start up and replaced the warm up regulator, cold start valve (critical) and fuel accumulator. BIG improvement, but still pop, pop and slow to catch. We ran the fuel pressures on it and found a nifty leak in the fuel line between the fuel distributor and "T" fitting. I replaced all fuel lines. MUCH BETTER.....we're getting there!

I finally bought a CIS mixture adjustment allen tool (3mm) and started playing with the mixture.......and better improvement....but the final dance was taking off the very original injectors, getting them cleaned (rust!) and inserting new seals.
Now everything is beautiful...............add some marvel mystery oil to the fuel and I am in business. But, I must say, I added new manifold runners, cleaned the throttle body butterfly valve just for extra measure.

For an old CIS....it takes patience and replacing some old stuff to get it like new. Check out the CIS Trouble Shooting Chart in
Tech. Articles. Its a permanent fixture in the glove box.

Best of luck
Bob
'73.5 T

[wckrause]

What does it do while you're trying to start? Does it just crank and crank, or does it fire up, run rough, stall, backfire?

[GregS]

Gents, thanks very much for the input. In response to your individual comments:

Joe - I haven't tried that yet. The mechanic claims that the cold start valve tested OK.

Bob - I had actually begun to wonder whether a component by component replacement might be in the cards, as the system is, for the most part, 28 years old. I've been hoping to avoid going through the entire system, but that may not be possible. Thanks for your checklist!

Bill - The engine will simply crank for several minutes without giving any indication of wanting to start. After several minutes of cranking, it will kind of catch and cough for a couple of minutes, backfire a time or two, and then start, idling very hesitantly. After some rough running for 5 to 10 seconds I can adjust the idle with the hand throttle, after which it will idle smoothly. Once the car has started and been warmed up, it runs very nicely. Any other thoughts?

Thanks, Greg.

[Sunroof]

Greg...
I am more intrigued with the thermotime switch replacement! I was told that my year (73.5) did not have a thermotime switch and this was mentioned by several mechanics who sort of "cut their teeth" on these models. You have me quite concerned if indeed you had one replaced! My CIS is far from perfect. In fact yesterday my mechanic reset the pressures in the WUR and the idle was jumping around like crazy this morning! It would cost thousands to replace every component but I will tell you that one thing to certainly check is the fuel tank for that "black stream bottom sediment" and your fuel filter. If its your original tank it must have rust! Clean fuel is critical for these systems to operate well. I change my filter every 5-6K for safe measure, besides they are cheap insurance. Please let me know about your thermotime switch.......and good luck.

Bob
'73.5T

[wckrause]

I'm not familiar with the early CIS cars, but from your symptoms, it does sound like something is wrong with either the cold start injector or you've got low fuel pressure.

You should be getting a healthy injection of fuel from the cold start injector, that should at least get the car to fire right away. Once it fires, then the warm up regulator should be causing a rich enough mixture to keep it running. But even if the rest of the CIS system is screwed up, the cold start injector will at least get it to fire.

How did your mechanic test the cold start injector? Is your system fuel pressure coming up good to the right level?

[Jim Sims]

There is not a thermo-time switch per se on a 73.5 T w/CIS. There is only the WUR (or control pressure regulator for warm running compensation as it was called in the original service/ training information); the WUR contains a bimetallic spring which is heated by a coil after the car is started. If your "thermo-time" switch and WUR were both replaced then perhaps the WUR was replaced twice. It should be noted that the cold start valve on this model receives its current from a switch wired into the starter circuit. This switch is only activated when the hand throttle (between the seats) is pulled out all the way. Your cold start valve may check out fine but if it doesn't receive current via this linkage system it really isn't operating (and enriching the mixture) when you attempt to start the car. Check out this system. Cheers, JIM

[GregS]

Good evening gents, and thanks again for your replies. I apologize for taking so long to respond but I got called out of town on short notice and just got back. Here goes:

Bill - I'm not sure how the tests were actually done, or what the pressures were. On the work order they did specifically mention that the fuel pressures were checked, and that the fuel mixture was also adjusted. He did mention when I picked the car up that the pressure checked out OK, which I assume means at between 4.5 and 5.2 bar. I will get back to them and get more specifics.

Bob - On my car, they replaced the thermo-time switch, Porsche part #911 617 117 00. It is located on the left-hand chain housing cover. Also, the car was originally delivered with MFI, in very late '72, and within about a year, converted to CIS - I wish I knew why!! It would seem that the systems on our two cars would be fairly similar, but - obviously - my knowledge of CIS is extremely limited, and perhaps there were some differences.

Jim - Thanks for your comments. I'll be following up with you some more, as I'm here in NM, in Los Lunas.

Thanks again, and please keep the thoughts and suggestions coming. Greg.

[Jim Sims]

Greg, I sent you an e-mail prior to rechecking this thread. The original 1973.5 CIS did not have a thermo-switch on the left chain cover housing. When your car was converted from MFI apparently a CIS system from a later year was used. The thermo-time switch you reference was first used in 1974 according to my references. Therefore the conversion within a year is puzzling unless an early 1974 CIS system (from a brand new wrecked 1974?) or from factory parts($$$!) was obtained. In any event, you have a hybrid system, and the hand throttle may not even actuate the microswitch for the cold start valve. It would bear investigating exactly what your CIS system, fuel pump system and wiring harness consists of. I also have the 1974-1977 illustrated factory parts catalogs. Cheers, Jim

[wckrause]

I think your're going to need to pull the cold start valve out and verify that it's injecting gas while the engine is being cranked. This will verify both the operation of the cold start valve and the thermotime, along with any wiring mods (or missed mods).

[GregS]

Once again, thanks for the thoughts and suggestions. Here goes.

Bob - It appears that we actually do have different systems!

Jim - I'll contact you, as I'd like to take you up on the offer of having a good look at the description of the system which is actually installed on the car.

Bill - Early this week I will be able to test the cold start valve. I'll get back to you guys with the results.

By the way, I've got the original purchase order for the car. A quick check of the phone book shows that the original owner still lives at the same location. Haven't yet been able to contact him, but I'll keep trying. It will be interesting to find out what drove the conversion from MFI to CIS. Thanks again, Greg.

[GregS]

After nearly two months, the problem has finally been solved. Over time, it became increasingly more difficult to get the car started, taking nearly 1/2 an hour. I gave up on the mechanic I had been taking the car to, as his last guess (which also proved to be wrong) was the cold start valve. I contacted Jim Sims who posts on the board and he very kindly provided me with wiring diagrams and a ton of other information about the CIS (thanks again Jim.) I had continuity where I was supposed to, and the cold start valve was actually dumping fuel as it was supposed to. As I said earlier, the situation continued to deteriorate until the car simply would not start at all. At that point, I loaded it onto a flatbed and delivered it to a guy here in Albuquerque, Russ Kelso, who runs a company called Precision Motorcar Investments (Yup, thats a plug for him). I had some running around to do in town, and got back home about 3 hours after I had left Russ the car. Before I even arrived back home, he had called with the diagnosis - a blown air box. It had cracked between the plenum and the base of the box, where it was nearly impossible to see without removing it. It was not the original air box, had no pop off valve installed, and, once it began to crack, had gotten worse over time, to the point where it was - literally - hanging on by a thread. In any event, I now have a new air box (with pop valve), and since the system was apart anyway, Russ also replaced the injection runner boots, injector seals, intake gaskets, the AFM seal, the breather gasket, air box straps, the breather hose from the engine to the oil tank, changed the oil and filter, and installed new plugs. He also cleaned the TB, AFM, intake runners, checked all of the injectors, ran a compression test (130 psi on all 6), reset the air/fuel mixture and the idle, and checked the emissions. Needless to say, I also have a new mechanic. Not sure what the moral of the story is (if there is one) but it sure feels good to have the car back (correctly) again. So, in closing, thanks again to everybody who responded, and especially Jim, who went a very long way, out of his way, to help. Another shameless plug for Russ Kelso, who I can recommend without any hesitation to any Pelicanites here in NM, or anybody passing through who runs into a problem. And a little bit late Happy New Year to everybody.

[Sunroof]

Greg.
Glad to hear everything worked out for you. Definitely install a pop off valve if you have not already.
I finally got my system working well after carrying my nifty 3mm mixture adjustment wrench and adjusting my mixture, but I have another problem I thought I would let you know about.

My gas tank is rusting and my fuel filter changes (every 3,000) shows that ugly fine black "river bottom sediment". As a result if I do not get my tank cleaned and resealed I was told that the dirty fuel will raise havoc on my fuel distributor and injectors. The tank removal is scheduled for next weekend.

Just a heads up and word to the wise. These older 911's and ancient CIS systems are very dependable but with age you have to be on the lookout for a myriad of problems.

Good luck and safe motoring

Bob
73.5 T