check engine light

I recently had the ignition coil and computer replaced on my van and it was fine. A couple weeks later I changed the air filter, breather and PCV valve and now the check engine light comes on. At first it would come on about every 4th time I'd drive it but now it's on every time as soon as I start moving. I'd rather not drop any more money into it right now and I have a second vehicle so I haven't taken it to the shop yet. Any ideas would be appreciated.

1990 B250
5.2L 318

I took it to work last nite because I was planning to go ahead and have my mechanic check it and it had other problems/symptoms and now sits in the lot at work dead. The headlights and dash lights dimmed and eventually when I would use the turn signal the brake and ABS lights would come on (huh?). When I tried to start it this morning it just clicked. So now who knows what's wrong with it at this point. Just wanted to update.

check charging circuit and battery seems your battery is dead

I forgot about updating this after getting the van fixed. The shop did replace the battery and it seemed to run ok when I went to pick it up but the CEL was still on (apparently they didn't notice this). They read the codes which pointed to the alternator. After replacing the alternator (twice) the CEL was still on and they got the same codes. They finally decided the problem was the voltage regulator which is inside the PCM. After replacing the PCM for the second time in 3 months and third time in less than 3 years all seems to be well again with the van.