i have 300,000+ miles on '89 SSE getting code 42
Could this be caused by the timing chain ?

How do I replace the ECM ?

original chain
DAMN even if i wasnt caused by the chain I'd change it anyway

I run Mobile 1 synthetic oil and it IS a chain not a belt and the tensioner design is good.
Why wouldn't the chain last forever ? <grin>

You Timing Chain HAS lasted forever!!!

During its life span, the metal in the chain tends to stretch a little bit. Over time(in your case - a LONG time) it stretches to a point that it becomes very sloppy, and Mobil 1 doesn't prevent this from happening. I don't mean to imply that this is your problem, as I don't really know the answer to this one, but it may be a contributing factor. Also, just for the record, how long have you owned this car and is it the orginal engine and transmission(not rebuilt)?

I bought the car new.

The engine is completely original, no work done to it. The transmission was rebuilt at 200K just because I didn't want it to fail.

I'm on my 5th alternator and 5th windshield the rad and gas tank & water pump had to be replaced at about 180K

My headlight bulbs lasted 11 years!!!! I attribute this to never closing the hood untill the lights cooled down ( I used to do theaterical lighting)


This morning I changed the ignition module but with no luck. Now the car will not start. Which further leads me to suspect the timing chain

I will get it towed to friend'* and may be across the summer he'll do the timing chain.
I looking at 6 to 7 hours labor plus the parts