Only Starts w/ Cold Start Injector Disconnected
 

‘80 911SC here.

I have a unique problem. I’ve been chasing a cold start issue, and I’m starting to get close to the resolution. I recently cleaned up my fuel system and had the fuel distributor rebuilt. All of my fuel pressures are in spec (system, cold, warm and residual bleed down). I’m still having a cold start issue, so I connected a wideband o2 sensor to diagnose the issue. I baselined the fuel mixture using injector opening pressure. During starting it was extremely rich and would die almost immediately. I played with the fuel mixture in all directions and nothing changed with the rich start/die issue. I re-baselined the fuel mixture, and I decided to disconnect the cold start injector power plug. It started immediately, and I was able to get the fuel mixture dialed in. I took the car for a spin, and it ran great. It seems like the cold start injector is dumping way too much fuel in the system. Has anyone ever seen this? Before I go replacing this injector, I want to see if anyone else has run into this problem.

Thanks.

The injector itself is probably good. The thermo-time switch (TTS) may be faulty and stuck closed.

Sounds to me like the tts (Thermostats time switch) is not opening after it warms up to shut off power to the cold start injector. I’d start by testing that. This link below has a lot of good information on how to do that.

https://forums.pelicanparts.com/porsche-911-technical-forum/594010-thermo-time-switch-1978-sc-3-0-a.html

Edit: Gilles beat me too it lol

Is the frequency valve system functioning?