My 1993 Regal 3.8L runs great for about 11 or 12 miles. After that, it starts running rough and stalling. It throws a code 18 and sometimes, if I keep trying to drive it, a 42. Once while in a drive-through, I tried to keep it running by feathering the throttle, and the cat heated up and burned off all adjacent oil.

After it sits for 5 or 6 hours, it'* good for another 12 miles. It gets me to work and back home, but anything else, I'm out of luck.

I've been working on the assumption that something is heating up and failing, then is fine after it cools down. This has been going on for months! You would think it would have failed permanently by now, but the run time hasn't even shortened.

From what I've been able to find, the OBD1 code 18 for '93 3.8L is for the Cam/Crank sensors & circuits.
Code 42 is for Ignition control circuit/Electronic spark timing.

I've replaced:

Cam sensor & pigtail

Crank sensor & pigtail

All 3 coils

ICM and harness

TPS plug

ECM

Ignition switch

Harness wires between ICM, ECM and the crank & cam sensors. (Soldered & heat shrinked to within 4 inches of ECM connector.)

The hot in run, test or start wires from the ignition switch to the Right Side underhood elec center and to the fuse block by the glove box.

All of the fuses, just because.

The 3 cooling fan relays in the R/H underhood elec center.

The fuel pump was replaced about a year ago.

I'm at my wits' end with this.
HELP!!!
I may have to revive my '68 Econoline!

Have the exact same car and had the exact same problem (no code 42 but same symptoms and code 1. Have you tried replacing the spark plug wires? I kept screwing around with all the signal stuff but it ended up being a very small arc from the boot to the ignition coil. My mechanic said to mess around with all the wiring and such and it ended up being pointless (but a good learning experience).

So yeah if you haven't done so already, make changing your spark plug wires a priority.

Apparently 8 and ) make a cool person face That was suppose to read code 18*

Haha! I'll try the plug wires. Thanks!

I replaced the plugs and wires. Really thought I had it when I found #4 wire not actually contacting the plug! Nope! Same problem. Thanks for your suggestion! I really thought that was going to do it.

Plugs/wires are not going to fix a code 18......we are talking cam sensor, crank sensor, ICM, PCM, cam magnet, interrupter rings on harmonic balancer, wiring, or connectors in the harnesses....which is just about everything you have done....

Were these new or used parts?

When erased, which code comes back first?

Tech II,
All parts were new, except the ECM, which was rebuilt. The 18 code is the one that always comes back first.
I borrowed a Snap-On "Brick" this weekend from a guy at work. I'm putting my results in a spreadsheet to see if I can make some sense of it. I DID notice that the O2 Sensor output fluctuated wildly, anywhere from 4 to 840 millivolts. I don't know if that'* normal or not, but it seemed odd. Also one frame showed several other codes that I haven't seen before. They only showed on that one frame. I'll post more when I get it all together.

Well, it'* been I don't know how long, but still having the same issue. Thanks to those who have made suggestions.

I've come to think, no conclusion, that the part causing the problem has failed completely long ago and that it is brought into play at the time or temp or whatever is triggering the problem. Otherwise, things would have gradually gotten worse to the point of complete failure months ago.

So, any ideas on what component comes into play after 20 minutes or 10 to 12 miles or so?

Interesting...

I'll have to remember to pull my 93 c/h body fsm to get more insight on this code. I always did love a good mystery