Cold start problem, 1975 911 with 3.0 L engine

[gluna]

The car is a very nicely restored 1975 911 coupe with a 1978 3.0 L engine.

I have a problem when cold starting the car, it usually happens overnight, when the engine is warm there are no issues at all.

Once "cold" I can not start it easily. I turn the switch on for 5 secs, the pump runs fine and when I crank it there is absolutely no response from the engine, this cycle repeats for 10-15 times and then engine starts to become alive (15 min could be spent trying), it fires 1 or 2 secs and then dies, it may start on the next crank and when it does idles close to 900 rpm, but if given a little gas it can either shut again or we can have a few backfires, this goes on until de engine is warm (5-10 min) and then it runs OK.

I`ve tried longer cranking cycles, 10-20 secs and the engine will not start, I´ve also tried running the pump 30-60 secs before giving a try and the result is the same.

Any ideas or suggestions?

[Mahler9th]

There are plenty of threads on this general topic in this forum.

Here is an example: http://forums.pelicanparts.com/porsche-911-technical-forum/1049314-cis-question-cold-start-valve-test.html

I have a friend that has a '74 with a 3L with CIS, and he has been troubleshooting his CIS.
He has been learning from the threads and some of the troubleshooting steps and tricks. And from some of the links to resources like this one:

https://jimsbasementworkshop.com/CIS/pages/test_troubleshoot.html

In my friend's case, after some diagnostic steps with a voltmeter he suspected a switch. He just replaced the switch and confirmed that the old one was bad because she fired right up.

If you are not going to try DIY, then finding a service provider with CIS experience is obviously your best bet.

[Mahler9th]

By the way, nice looking car. And good luck.

[Showdown]

I had almost exactly this same problem and found that my airbox was riddled with cracks and needed to be replaced.

[gluna]

Thanks for the help, will start working on the issue and will keep you posted.

[GAJon]

Double check all the connections. The system has a bunch of "sensors" in series and if one of them is disconnected, the cold start behaviour can be weird. For me, it was the TTS on the front left valve cover. Fixed that and made sure I had a good battery and mine was fixed.

Also good to check the quality of connection. Some of the spade connectors may be well corroded.

[gluna]

Checked the airbox and all good here, relief valve also working properly.

[Joe Bob]

Usually a hot start issue but have you looked at the check valve in the neck of the fuel pump.

Does it start up easily with a shot of ether?

[boyt911sc]

Gluna,

Check the following:

1. Perform a smoke test to locate hard to find sources of unmetered air.
2. Measure your fuel pressures (system, cold & warm, and residual).
3. Test your CSV. If might not be working.

Keep us posted.

Tony

[Joe Bob]

http://forums.pelicanparts.com/porsche-911-technical-forum/996790-cis-guages-these-any-good.html