bureau13

So, I have a 931 S2, which SHOULD have the fully electronic DITC system...but it doesn't. The PO mentioned in the add that it was replaced with something, but nobody knows what, exactly. I have a theory that it was retrofitted with a S1 ignition, but I don't know enough to say for sure. The reason for that theory is that the distributor has a vacuum advance/retard fitting, and I can't imagine someone putting an aftermarket ignition that wasn't fully electronic.

Below are some pictures, maybe they will provide some hints:




Ignition device behind the driver's side headlight. I don't see any names or part numbers on this, unfortunately.




Upper right is the vacuum actuator for the distributor. The vacuum line routes to this silver cylinder, teed in with another vacuum line. Meanwhile, the other side has an unattached vacuum port and 2 electrical connections...one goes to ground, the other to a wire harness shown in the picture.

There is a part number stamped onto the side of that cylinder, btw, but doesn't seem like a Porsche (or VW or Audio) part? 3738591...comes up as a Mopar EGR valve?!

If anyone has any idea what I'm looking at, I'd love to get your feedback...

PaulD_944S2

I believe that the "silver cylinder" is vacuum switch which is part of a retro-fit NOX smog device designed to cut off vacuum advance until the engine is in high gear or above a certain temperature. Had something similar to that on a Plymouth 'Cuda, and I recall them being an add on the early smog years to help reduce NOX emissions.

You might want to check with a knowledgeable smog test station, or a smog referee to see if it is still required. This was the clumsy attempt of reducing smog emissions in the early years.

V2Rocket

jeez paul i was really scratching my head looking at that one wondering why somebody would have a vac switch to the vac advance...had nothing.

good thing we've got er...more mature folks with 70s smog experience to set us straight

bureau13

Oh, that makes sense! But really weird to put that on a car that was originally vacuumless distributor, isn't it?

As for whether we need it...they're not testing emissions here at all now (South Florida) so I'm gonna go with NOPE...

jhowell371

Ah yes, the dreaded NOX. I too remember all kinds of Rube Goldberg solutions to ever tightening smog regulations that started in the mid 60's. Lots of vacuum lines, PVC (positive crankcase ventilation) valves, charcoal canisters, air pumps, fuel and vacuum shut off solenoids, carburetor air pre-heater hoses and more. Back then I was more interested in yanking that crap off and then re-jetting the carburetor to compensate.

bureau13

Can anyone familiar with the ignition timing box behind the driver's side headlight (first picture) tell me if this looks like an S1 ('80) or S2 ('81-'82) box, or neither?

V2Rocket

your go-to guru if you haven't tried already is:

dan DOT beckett AT ideola DOT com

http://garage.ideola.com/top-Contact.html

the guy lives and breathes for 924s.

bureau13

Dan is actually the guy who pointed out the ignition changes in the BaT thread. He previously asked for a picture of that box, which I sent, but he must be really busy now because I haven't been able to get hold of him recently...figured I'd throw it out here as well.