Check Engine light/ knock sensor

[machine]

I've got a 91 Previa all trac, it runs great, we love it. It's time to get it smogged. The check engine light is on, which is an instant fail. I've tried resetting the code, with no luck. Still comes on. It will randomly go off for a while, and then come back on, but we can't figure out a reliable way to get it to do that (so we could get it to pass smog...).
So it seems I will have to fix the problem. If the problem is in fact the knock sensor, the manual doesn't have much info on this. I've been told that you have to drop the engine to get at it. Is this true?
I'm a skilled metal worker, is there anyway I can cut an access hole?

thanks
mike

[future_spiegel]

you know, ive taken cars with cel's to smog and as far as i know its not an instant fail unless its OBD-II (96 or newer).

[machine]

we double checked with the local, and decent, smog place. and they said 83 and newer with check engine light on is an instant fail.

we ended up taking the van to a place well reccommended called "oceanworks" in berkeley. they fussed with it, and were able to replace the sensor without totally dropping the engine... it was still a pretty big deal though. a full r+r would be about 800, they only charged about 500 plus parts. and they did it in a day. they seem like a top notch shop to me.

the check engine light is staying off now, let's hope it smogs ok!

[future_spiegel]

oh man, if i had known i wouldve given you a contact i have in rwc where you can smog cars no problem. so what did they do to the van? just the knock sensor?