1985 308 Running Issue - Digiplex Going Bad?

I guess for the purist and for someone that like to keep everything stock plus for those who lives in CA, if they go Euro spec, they’re afraid it may not pass smog test.

 

I have never has a smog tech use a timing light on my QV or my 2007 Mazda. I think because the timing is "set" and not adjustable by rotating the distributor that there's no reason to check it. Or it could be that the smog check has changed since the last time I had a car with adjustable ignition timing and no one checks it at all anymore, I don't know.

 

You’re right Brian, I never seen a smog technician use a timing light plus on a 308, is useless because you can’t adjust the ignition timing anyway as it’s fix.

 

Suddenly I had a "hunting" idle on my '85QV and very poor power below 3000 RPM. I checked the O2 sensor, the cold start injector, the distributors and wires, the auxiliary air valve and ran new grounds to the Digiplex boxes and coils (which I also tested). I replaced the sensors, although they tested okay for resistance. I began to wonder if it was actually a fuel problem.


I had the Digiplex boxes rebuilt by David Feinberg's company. They were done very quickly. He advised me that the old boxes tested okay.

In any event, when everything was back together my problem was solved. I'm guessing it was either a Digiplex or a sensor, even though bench tests suggested that they were okay. So I'm not sure that things fail obviously or completely.

 

I've got plenty of experience with the Sarasota Italian Garage (David Feinberg's shop) boxes. Both the Digiplex and the Microplex units. They're the real deal. Complete replacements using modern electronics, not rebuilds of the old OEM circuit.

If you're replacing your working OEM boxes with the Sarasota Italian Garage units that use the same curve, you won't really notice any difference in performance. They do use a more modern fuel map instead of the eight curve stepped map of the old units, but honestly it's not terribly noticeable "seat of the pants" from the cars I've driven back to back with old and new units. It's just a bit smoother. I'd consider the modern map icing on the cake rather than a must have feature. Now If you swapped out US units for units using the Euro curves, you will definitely notice. I find the Euro curve pulls a bit longer into the RPMs than the US curve does. It certainly doesn't make it a totally different car, but it is noticeably better. The 2v cars especially make a nice leap in performance with the Euro curves.

Cam timing and ignition timing don't really have overly much to do with each other (this is admittedly simplified, ignition timing and cam timing do actually relate to each other slightly, but not enough to make a difference in a car without modern computerized valve timing.) No matter what the cam timing is, the valves are closed when the spark goes off. Ignition timing is about firing at the right point before TDC so that your pressure wave meets your piston right at TDC, then backing off as much as needed to control pre-ignition and meet emissions goals. The latter being why the US ignition curve is not as advanced as the Euro curve.

A shop that is concerned about following federal emissions laws would want to put back the same version box they took out.

Although bench testing can give you pretty good confidence that a Digiplex box is ok, it isn't 100% the same environment as in the car. Intermittent problems or sometimes EMI/RFI issues are not guaranteed to show up on a bench test of the unit. Glad to hear your problem was sorted!

 

Good to know. Thank you.