911 elec./ start problem

spitzbube · 01-15-2011, 04:33 PM

posted for the first time a few days ago , concerning a starting issue with a 77 911. this car came with the problem , and i don't have much if any history on it , except someone tried to get it running a while ago [ unsuccessfully] I asked for and received help from members of this post for a wiring schematic . after looking at the wiring i discovered that the coil and the dist. had been grounded . i put this back to the way it looked on the schem. car still doesn't fire . could the coil and or the capacitor be fried ? i don't hear any noise when ign. is on before i turn the key to engage starter. should i be hearing a fuel pump or high frequency noise from capacitor ? thanks tom .

ossiblue · 05:00 PM

If you have the stock Bosch CDI, you should typically hear a high-pitched whine with the ignition on. However, not hearing the whine is not a certain sign the CDI is bad. I assume you've tested for spark and found it missing? If not, please let us know what you have done in the way of testing so far. One thing you can easily check is if you are getting power to the CDI. You should have a 3-pin unit. Unplug the connector and check for voltage at the middle pin of the connector--terminal "B"--with the ignition switch on. You should have 12V at the connector. If you do, then proceed with a test for spark.

Regarding the fuel pump, it will not go on with the ignition switch as it is powered through a relay that activates the pump via the starter circuit and air flow sensor. If you remove the red relay in the trunk, and jump terminals 30 and 87a, the pump should come to life when the ignition is turned to the "on" position.

Don't get discouraged. Just pick one course to follow--in this case, getting the car started, and begin to narrow down the variables. Sounds like ignition may be a problem so that's a good place to begin. Lots of help here, just ask, respond with any results or information you can provide, and move one step at a time. Your car will be running before you know it.

spitzbube · 01-15-2011, 09:44 PM

lj both cdi and fuel pump check out . tom

-84 Carrera · -84 Carrera's Garage

Could your problem be the ignition switch it self?

I had a problem two years ago with the actual ignition switch. The switch has a feature which will prevent you from turning the starter over when the motor is engine is running. If you take the switch apart you will find a small spring loaded pin that is supposed to interact with a turning disc. If the disc has too much free play you can end up with a situation where the ignition will come on, but the starter will never engage. At the time I couldn't afford a new ignition switch since it meant replacing the whole assembly including the steering lock, so I simply removed the small spring loaded pin.

Regards

Claes

spitzbube · 01-16-2011, 09:00 AM

Claes, starter works just fine , it;s just that there is no spark ?. is it possible coil is shot ? any one know how to test this pup ?

T77911S · 01-16-2011, 04:31 PM

the coil is suppose to be grounded. i am curious as to what was grounded on the CD that you thought should not be grounded.
what brand CD unit do you have?

spitzbube · 01-16-2011, 05:06 PM

t77911s , the wire going down to the dist. from the cdi doubled back to the coil bracket and was bolted underneath it . there was a wire going from the other side of the bracket to one of the poles [ the one thats suppose to have the brn /red wire from the cdi via the dist. ] on the coil . cdi is a bosch .

spitzbube · 01-17-2011, 08:45 AM

t77911s , whent back and took another look at ign. and changed wiring after your post . i grounded the neg. pole on coil to coil bracket , and ran the wire coming off the dist. to other side of coil bracket . not sure if any of this is correct . please advise . tom .

T77911S · 01-17-2011, 01:25 PM

the neg side of the coil to ground is right.

i pulled my original wiring off a long time ago and put in an MSD system, so i hope what i tell you is right.

the wire from the points is a coaxial wire. it has a center conductor and an outer shield that is grounded. the points wire goes to the CD unit. i think this wire is white, but dont hold me to it. this goes to pin C of the CD unit. pin A on the CD goes to the + on the coil. pin B has switched 12volts on it.
these wires are old and can dry and crack causing them to short out.

here is a great thread on everything you ever wanted to know about the ignition system.

History of Bosch CDI ... toubleshooting info, parts list changes, and schematics ...

one test to do is to check for continuity between the neg side of the coil and the CD unit. you can also ohm out the other wires and make sure they are not shorting to each other.