CIS playing up
 

When I went to start up the SC yesterday had a strange experience. With the key in the ‘on’ position what I assume is the fuel pump started running & I went to the rear of the car & could also hear buzzing from the injectors (? Like if you manually lift the sensor plate). I let this go on for a few seconds while I was working out what was happening then had to crank for a while to get the car started- it was flooded. This has been the only time this has occurred & it didn’t repeat later in the day. I guess there is an ‘iffy’ electrical connection somewhere- does anyone have any pointers of where to start looking?
Thanks alot

i think your injectors can only spray when the air sensor plate is moving up. if i had to guess, i bet the plunger in your fuel distributor is getting sticky.

Correct. If there is no air coming throught the plate (i.e. engine is turned off) there should be no fuel coming out of the injector even though the pump will run.
You can pull the injectors (easy on cars with nylon lines, not so easy with metal lines...) and place them in safe containers and verify they are not leaking. You can also test to see if they have even flow and spray in a nice cone pattern. See: http://forums.pelicanparts.com/porsche-911-technical-forum/142040-tested-my-cis-injectors-today.html

If they are infact leaking, you have one of four possibilities
- Bad or stuck open injectors (not too likely that they would all be doing it though)
- Sticking distributer as unfixed said
- Misalligned air sensor plate or air plate stop that is holding the distrubitor open
- Way too high control pressure (normal cold control pressure for an SC is 21-25 psi, it takes about 45 to open an injector) This could be caused by a bad WUR.

There may be others, but those are all I can think of off hand.

Pat

Thanks for the input guys. Good call on the plunger- I'll check this out as I did have an oil 'overfill' condition a while back.

When this happened the car had been sitting for a week. Would this discount the high control pressure theory? I have a CIS tester on the way, as I want to verify that the system is within spec anyway.