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No Spark

R

ronjon1163

New member
Hi

1987 Porsche 3.2 Carrera Sport Coupe, was starting no problem, then started and stopped. Has failed to start again since. There is no spark, the injectors are working and supplying fuel to the plugs, battery is healthy, there is 12v to the coil but nothing coming out the king lead, I have replaced the coil, distributor and rotor arm but still no spark. I have tested the resistance in the HT leads which is correct, I have placed a spark plug into an HT lead and also straight into the king lead from the coil, earthed it but still nothing, any ideas
 
Well that only leaves the CDU (capacitor discharge unit) or the RPM sensor as a possible culprit. It is sometimes possible with the ignition switch on to hear the CDU making a whistling high frequency sound if it is working. The CDU is the finned item located near the coil. The RPM sensor is the round module to the left of the CDU just above the 3 fuses. It can be checked with a ohmeter. Resistance values 170/210 ohms between terminals A & B, 220/300 ohms between A & C.
 

ORIGINAL: ronjon1163

Hi

1987 Porsche 3.2 Carrera Sport Coupe, was starting no problem, then started and stopped. Has failed to start again since. There is no spark, the injectors are working and supplying fuel to the plugs, battery is healthy, there is 12v to the coil but nothing coming out the king lead, I have replaced the coil, distributor and rotor arm but still no spark. I have tested the resistance in the HT leads which is correct, I have placed a spark plug into an HT lead and also straight into the king lead from the coil, earthed it but still nothing, any ideas
Click to expand...

Hi
Geoffs answer i think is for a 3.0 sc and you say you have a 3.2 Carrera so I think your fault is the Reference Sensor on the bell houseing thay get crushed by corrosion and then no spark.

Charles
 
You can check the speed sensors the plugs are on the left hand side of the engine bay just above the fuel rail a line of 3 plugs its the bottom 2 and the terminals are read from the bottom up so 1 2 3
you should have 960 +- 96 ohms between 1 and 2 , >100,000 ohms between 1 and 3 , >100,000 ohms between 2 and 3
Are you getting 12.6v at the plus side of the coil to earth when ignition is on
It shows all this in the Bentley Manual
 
Hi
Geoffs answer i think is for a 3.0 sc and you say you have a 3.2 Carrera so I think your fault is the Reference Sensor on the bell houseing thay get crushed by corrosion and then no spark.
Click to expand...
Yes, I assumed that they stayed the same through to the end of 3.2 era. Hope I didn't start a wild goose chase.[:(]
 
Thanks guys I will start these tests on Tuesday after work and I will post the results. I have the Bentley manual but don't want to start replacing things just for the sake of it.

Thanks
Ronnie Ferguson
3.2 Carrera Sport Coupe
 
hi guys
I have tested the sensors (reference and Speed) i am getting the correct reading between terminals 1 and 2 on both senders but dont seem to be getting any readings between 1 and 3 or 2 and 3. I dont understand this, looking at the sensors they appear to have been renewed as the cables look very clean and the grommet as they pass into the engine compartment is split and not sitting properly. I felt for the small screw like sensor on the crankshaft which is there I cleaned same but still nothing, I phoned Porsche but they dont think that both sensors would just suddenly go at the same time but did seem to think that it was possibly a sensor, does anyone know if there is another test I can do to narrow this problem, remembering that it was going but just suddenly stopped for no apparent reason.
Cheers
Ronnie Ferguson
1987 3.2 Carrera Sport Coupe
 
With reference to Graham's provided test values your readings are correct. Your meter will probably see the expected very high values for 1-3 and 2-3 as open circuit.
I have not seen mentioned above the checking of all the earth's to the system. You have probably checked them but I thought I would state the obvious anyway.
 
Hi

The earths are fine, although i replaced the DME relay about a year ago the car has not moved, but i tested it again just in case by removing the plastic cover, both relays within are closing so it aint that. I have now to test that I am getting 5v AV through the sensor when ignition is on. Heres hoping

Cheers
Ronnie Ferguson
1987 3.2 Carrera Sport Coupe
 
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