Help!!! All you CIS guru's
 

I am about as frustrated as one can get with this CIS system! Its the first year it was introduced (1973.5) and I have done alot lately in trying to get this cold start problem fixed.

First, the car sounds like its not getting enough gas to start, back fires and after two or three turns of the key and playing with the hand throttle. After that it gets going after much hesitation. I replaced the airbox, installed a new cold start valve, pop off valve, had the injectors cleaned, new injector seals, ran the pressures have the right mixture setting and everything is right. I replaced the warm up regulator, new intake sleeves and still it putters and putters on cold start. Once warmed up though it runs like a bat out of hell.....so what the heck!? That leaves, fuel pump, fuel distributor or leaking injector. I even cleaned the plate and butterfly well and added new fuel lines.

That year and that year alone never got the thermotime switch. Its been very frustrating as you can imagine. Maybe one of you guys has gone through the same thing. I am thinking leaking injector because they are the original units and were loaded with rust. Any ideas? Greatly appreciate the help.

Thanks
Bob
'73.5T

"ran the pressures"

Does that mean you checked the control pressure at cold start? as well as system pressure?

Do you know what the spec is for control pressure vs. ambient temp for a '73.5?



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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

Good summary of your findings. Leaking injectors are more likely to give hot-start trouble (after 20 mins of shutoff) than cold start trouble, in my experience. I'd check two things: I'd pull the cold start valve, stick it in a jar, in fact I might pull all injectors and put them in jars, and have an assistant try to start the engine while you watch the CSV. Is it spraying during cold start? If not, this is a problem.

I would also make sure that the Auxiliary Air Regulator is opening and closing. the AAR (or whatever it is called) is your idle boost during cold running. And as you know, the CSV is your choke for starting.

On the bright side, your CIS system is about as simple as a fuel system can be. No electronics. No O2 sensor. Purely mechanical. These are generally very reliable systems.

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'83 SC

Does a 73.5 have an AAR? I thought that's why they have a hand throttle.

Question. When your car cold starts, does it fire up quick and then stumble, or does it slowly start to idle. In other words is it VROOOM....stumble...stumble....idle or is it just stumble....stumble....idle?

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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

as soon as you let go of the key, you are done with the cold start system. after that, whether it spits and pops or runs god, is up to the warmup regulator. this is assuming all the pressures and tuneup specs are in order. the new WUR is different than the original. superceded to the later style with an adapter kit to attach the fuel lines. did you set the CO to 3.5% on an exhaust gas analyzer? the pin on the WUR may have to be moved inwards a hair to get good running when it's cold, regardless that it's new. there's plenty of info on doing this if you search warmup regulator.