Engine starts when releasing ignition (key)
 

Hi. I need some help. I recently had my engine out of the car to change clutch and some other work (cleaning, replacing some parts). It is a 911 SC from 1980.

After it wouldn't start and backfired a few times.
There was only a spark on random occasions. We started to troubleshoot the ignition system. The coil, distributor and wires looked good. We suspected that the CDI box was the problem.

But today the engine started easy, but the idle was quite high (2000rpm) at first but dropped and now she runs like before.

But there is one strange thing, the engine does not start till you release the ignition (key). On ignition is cranks over, and when you release it the engine starts.

Is this normal? What can be the problem, we didn't change anything related to the ignition. And I have double checked that all the wires are connected correctly. Have i missed anything?

//Wenta

Did you hook the main ground from trans mount to body up?

Yes, the transmission ground is connected

I'm actually having a related problem (but I haven't fixed it, so take that into account.:-) )

Pull your harness plug from the bottom of your CDI box and check for battery voltage at pin 15 when the key is on. That tells you that power is getting to the CDI when it should to run. Now have someone crank the engine and make sure you still battery voltage at the same pin. If you don't, it means somehow your car doesn't have spark while cranking. You may have a bad connection that, under the load of the starter, doesn't want to power your CDI pin. Since you had the engine out recently, it's reasonable to start second-guessing your battery to starter cable connection, the starter-to-alternator on the same post, or the alternator to relay panel wire. As the other poster suggested, the ground from tub to trans could be suspect too.

Start there and good luck.

Here's a great link: http://forums.pelicanparts.com/9031477-post20.html

Thanks! I will test that next week (My car is at my fathers place)

Good luck with your car :-). And please post if you find the problem.

Did you reverse the cold start injector/sensor plate wiring connectors on the back of the engine?

Which connector is that?

Sounds like a bad ignition switch to me.

There's two connectors one for the cold start valve and one for the sensor plate they can be easily confused because they're both blue plastic fuel injection plastic.

http://forums.pelicanparts.com/porsche-911-technical-forum/755096-what-blue-connector-sensor-plate.html?highlight=sensor+plate+connector

I agree, that's the first place I would look, and it's an important clue. Check the operating voltage on that CD box, both with the car running and without, and also during starting. I suspect you have a grounding problem.

-Wayne

Update

Hi thanks for all the answers so far. But she still isn't starting. The CDI gets voltage when the ignition. But when I turn it to crank the voltage disappears. We checked and fixed the transmission ground, and the ground next to the cdi box, tried without starter motor just to see if the box gets voltage. Nothing have worked so far.

The cold start injector/sensor plate wiring connectors are correct, they does not fit eash over on my car.

I have studied the wiring diagram and it looks like wire number 50 is the one that goes out from the ignition when starting. But it only seams to go to the fuel relay. Where does the signal to the cdi come from?

Problem found!!

It was a problem from when we removed the old alarm. We put the ignition cable on the wrong fuse. That she started before we did the engine must have been luck.

Thank you all for the input. The summer is saved :-)