Questions and Answers
Porsche Has No Spark
Q. Dear Vincent Ciulla, I wonder whether you can offer me some clues as to the problem that I am experiencing with the ignition system on my 1989 Porsche 930 3.3 litre turbo.
The system on my car has a Capacitive Discharge Ignition (CDI). It has the stock Bosch ignition box. This system uses an over-boost switch which is located on the inlet manifold. It also has an over-boost relay (P/N 911 615 118 01), which is yellow in color and is mounted vertically and located on the left side inside the engine lid. Now, the problem that I have is..... no spark!
A list of what I have checked and some clues as to the problem;
* When the ignition key is turned on, the CDI will hum. Obviously, the CDI is receiving power. When the ignition is switched off, the CDI will continue to hum for approximately 5 seconds. I guess this would confirm that the time delay relay is good.
* To the ignition coil! Using a test lamp, there is no pulse to either positive or negative terminal on cranking. HOWEVER!, when I removed the negative wire there was a definite and strong pulse to the coil. After reconnecting the negative wire, again no pulse to either terminal of the coil.
* The distributor magnetic pulse connections were checked. Using a digital multi meter, a reading of 587 ohms (within tolerance).This reading was checked at both the distributor and at pin numbers 3 & 6 of the CDI harness plug connector. No doubt, my distributor is good.
* The terminal of the over boost switch has no resistance to ground. I ran the wire to ground only to get no pulse to the coil from the positive wire. I guess this would confirm that my over boost switched is also good.
HOWEVER, I do suspect that my over-boost RELAY (yellow) is faulty. I have a question that I'm hoping that you can answer. Does this relay have any link to the ignition system or does it simply cut-off the fuel supply on over-boost??? Some Porsche Parts specialist call this relay (911 615 118 01) an "over boost protection relay", whereas others call it the "air flow sensor plate relay". If this relay was removed, obviously the car would not start. But would there would a no-spark situation or a spark but no fuel???
I'm confused as the whether this relay has a link with the fuel system or the ignition system.
If you can offer me any assistance or if you could refer me to someone who has good knowledge of the Porsche 911/930 turbo, I would be extremely appreciative.
With regards,
GeoffA. I checked all my books and my database and I don't see a model 930 so I'm going with the 911 with the 3.3 liter engine and that does not have a CDI system. In fact, I don't remember any Porsche having a CDI system.
The Over Boost Relay is there to prevent the turbocharger boost pressure from going to high. When an over boost condition is detected, the relay will cut fuel until boost pressure goes down. There is also a mechanical pop off valve mounted in the intake that will open if the intake boost pressure exceeds limits. The over boost relay does not cut out spark. If it did, the fuel that accumulated during the time the spark was cut off would ignite and cause damage to the engine and down stream exhaust. In other words, a very large backfire.
I have seen the ignition ballast resistors go bad. The ballast resistor is supposed to lower battery voltage to about five volts. If the ignition system gets more than that, components start to burn out.
When you disconnected the negative terminal of the coil and got a pulse, that indicates to me that the pick up coil in the distributor is bad or the power transistor in the ignition module is bad. Also that you get a pulse indicates that everything else seems to be working. By opening the circuit by disconnecting the wire, you're doing what the ignition module is supposed to be doing, opening and closing the primary ignition circuit.
I think at this point the best thing to do is swap out the ignition module and, assuming the pick up is good, you should get spark.
Additional Information provided courtesy of ALLDATA
