Bassballplaya27

Now i knew something was deathly ill with my car when it sputters at a 1/4 throttle (about 1100 RPMs), but the funny thing is it only does it when its warmed up. Tight as can be when its cold, after 30 min of driving it acts up. Sooo i drive down to Shucks and use their OBD1 Tester Thing and he prints my report out, all is well. IT Says i have Code 42- Electronic Spark Timing circuit grounded, I ask the guy what it means and hes like i dunno and im like is it the opti-spark and hes like the spark plugs you mean .... By now im frustrated and leave.

So i need a little advice what does an- Electronic Spark Timing circuit grounded mean???? Is this the Opti or what??? Please Direct me to a generel source of error.... Oh ya its a 94 Z28.

Robs97Z28

haynes man...42- Ignition control circuit.... checkthe wiring and connections between the ignition moule and the emc/pcm. if this checks out good, replace the ignition module.

wile2k

Well, I *think* this is related to the ICM. And it makes a bit of sense that it happens after 30 min or so. Have you had the ICM (Ignition control module, little black piece located by the coil) off? The ICM has to have thermal compound between it and the bracket as that is how it dissipates heat. I'd guess that it is heat soaking and causing it to malfunction.

Just a guess but the DTC42 does point to the ICM and this makes at least a little sense .

Good luck.

SC97TA

I had the same DTC42. After exhausting everything it was suppose to be related to i.e. ign. ctrl. wiring problem, ICM, coil it turned out to be the opti it was obvious once it was removed.

Just my experience the DTC thrown isn’t pointing directly at the problem...can be very frustrating good luck.

Kris

SMOKNZ

I had the same problem, car would run really good for about 20 mins and then start missing really bad and would become undriveable. I had the same code and replaced the coil and ignition control module. neither helped. Turned out to be the opti, I removed the opti and the rotor bearing was broke and part of a screw were floating around inside.

Bill

Vomit God

I'm kind of having the same problem right now..
It was happening a few hundred miles ago..
I changed my oil, it went away..
Now it's back to doing it again..

Warms up and mid to moderate throttle under load gives me misses (or something : / )...
It's almost rythmic.. It's probably plugs and wires, but I'm guessing it's expensive :L

Can we get a group opti purchase going maybe?

Also.. Can't GM use a tool to diagnose if the high or low resolution of the opti is bad? One was bad on mine last time. (30K miles ago)