Thanks for all your advice Fred. Much appreciated. Will let you all know what I get up to when I get back home

Hi Guys and girls,
Does all of this info apply to a 85 cerrara? I've got the same no start situation. No spark to the plug. Does the 85 have the same CDI unit and where is it???
Frustrated. Hoping to tool around this weekend!

Where it is.....
 

The Bosch CDI is used in the model Porsche that you own. Look in the engine compartment, left side, next to the fuel filter. You may have to remove a black plastic shield that covers the engine compartment electrical components.

Before throwing money at the problem, do some diagnostic work. Turn the ignition key to the run position and listen for a high pitch whine from the Bosch CDI. If you don't hear the high pitched sound, check the fuses front and rear. If it has been a long time since a tuneup, pull the distributor cap off and check the rotor and cap contacts.

Good luck!

It's been a spell since we've had the ol' Bosch vs. MSD argument.
I favor original. Can anybody here make the same claim I can? That is, my original Bosch CDI unit has been functioning flawlessly since July of 1972. I carry a spare Bosch unit just in case, but I'm the paranoid sort...

In this corner, M!S!D!....
 

PWD72S,

Just for the record, I believe that Bosch makes a very high quality product. And, if the Bosch CDI in my car had not failed, I would not have purchased an MSD 6A. But, it did fail, and since I am the adventurous sort, and since I usually have more "wanna do" projects than $$$$, I elected to replace the Bosch with an MSD. The dollars saved bought a set of Magnacor plug wires and left a little in the bank. So far (knock on wood!) the MSD has performed flawlessly, has improved the idle and seems to give slightly better fuel mileage to boot. Someday I will send my Bosch unit off to be rebuilt just so I will have a backup unit "just in case". Meanwhile, I'll enjoy putting down the road feeling confident that the MSD won't let me down.

OK...looked in my Haynes manual. My '85 Cerrara has a "DME control unit" under the driver seat. There isn't a CDS unit on board as far as I can tell.

I don't have power to the coil or sparkys , so I am assuming it is behind that ie. the DME control unit.

There is also a DME relay and an Altitude correction box!? under the driver seat.

Anybody out there know how to test this type of system?? I sure dont!

The 3.2 Carera engine uses the DME (aka: ECU, Motronic) under the driver's seat to drive the coil directly. There is no CD box or equivalent. The DME contains the ignitor stage (a transistorized switch). Later cars (964, 993) have the ignitor as a separate unit. These can be tested by triggering the ignitors. On a 3.2 engine this is not possible to my knowledge.

There is no voltage present at the coil unless you crank the engine and the DME is working properly. All you can test is the coil resistance on the primary and secondary winding. Your Haynes manual should have the proper values.

In your case dynamic testing would be to crank the engine and check whether the second stage of the DME relay turns on. You can put your hand on the relay and can feel it click. The first click happens when you turn the ignition to ON. The second click should happen, once you crank. If nothing happens replace the DME relay. Maybe a friend nearby has one you can borrow. If not buy one. Cheap insurance and always handy in the glove box it beats calling AAA.

Onceyou confirm the DME relay to work you need to check for a spark while someone else cranks the engine. You can connect an old spark plug to one of the plug wires and place it onto a metal surface of the engine. Don't touch it while cranking to avoid electric shock. Another way is to get one of the little gimicks that clamp to the spark wire and indicate high voltage. This might be a little safer.

Good luck,
Ingo

Holy %&$* Ingo. you're good. I'm pretty confident that it doesn't have spark. Is that a good indication that its the DME relay or could it also be something else!!

Thanks, Rob

Rob,

I would bet in 9 out of 10 cases it's the DME relay. They are known to go bad over time. Some can be repaired by resoldering but I have also seen them with broken wires on the relay coil.

As I said buying a new one is good insurance since you will need one sooner or later anyways. Get one here at PP and you might be back on the road in no time.

Good luck,
Ingo

Update...Went out with Mike (my son) and did some testing. The DME relay clicks when you turn the key on and again when you crank the engine. Also tested the coil.. It does not light a tester going from pos to neg. when cranking. Does this help? Anxiously awaiting a Memorial Day drive!!

Check if the fuel pump is running when you crank. I don't have a schematic in front of me but you might simply have a blown fuse that feeds the second stage of the DME (fuel punp, O2 sensor, ignition). Check the Haynes for which fuse powers the second stage of the DME relay.

When I turned on the ignition, the only sound I heard was the click of the DME relay and I also the Idle Positioner humming (not continuously. It cuts out momentarily every couple seconds). No hear no fuel pump. Also there was no power to the fuel pump fuse.

After reading a Pelican Article, I jumped the fuse and the pump started hummin away. Following the articles advice , I attempted to start the car with fuse jumped. No start. According to the article, this means its probably not a DME problem.

Where is the fuel pump anyway??

So.. we have no power to the fuel pump fuse. What do you make of all this??

Thanks again, Rob

Rob, let me be a little more precise: The fuel pump and the ignition get powered by the second stage of the DME relay. So the pump only runs while the DME senses flywheel rotation (cranking or engine running).

The fuel pump is under the car towards the rear on the passenger side in a metal craddle. It's a little bit difficult to discern its sound. Its a high-pitched noise. You can jumper terminals 30 & 87b on the DME relay to make it run with the ignition set to ON.

Once you crank you should hear the fuel pump noise. I keeps running for another 30 sek. after you stop cranking. Let us know what you find.

THere is definetely NOT any sound of fuel pump after cranking. I went ahead and jumped 30 and 87b. When I did this, I heard the fuel pump running but the car still wouldn't start. So it seems like that relay is defective. But shouldn't the car start when jumpered? I'm hoping its not the DME unit.