Here is the Pro Tech answer to my latest question:

There you go thinking again! LOL, but seriously I'm fresh out of ideas….anything is possible, bad PROM, wiring, or some other reason the car is running rough…fuel, ignition, injectors, just plain worn out, etc, etc…Did you ever think that you may have a mechanical problem actually setting that code? The cam can wear out, become flat, etc…the crank can get too much play in it to keep the timing correct for the sensor. With the amount of miles on the car, this could in fact be the problem and internal engine repair might be necessary. Unfortunately, it'* time to bring it to a shop and have a more qualified person than you look at it, or just dump the car. This now ends your free help!

could have been nicer about saying hes out of ideas

I went back through all the circuits connected to the ICM. I made up a long test cable that I could use with my multi-meter and place one end in each of the ICM terminals and tested it against the connector that connects to the PCM. All were good. I did the voltage test and shook and jiggled wires and saw no drop or movement of the volt meter'* needle. I decided to switch out the ICM for the old one. The engine started and ran and Code 18 appeared. I decided to switch out the cam sensor by taking the one I had back and swapping it for another (of the same brand) but still the same thing, Code 18. Maybe the second crank sensor is bad; but the first one ran for a few months so I really don't think it is a sensor problem. Maybe these AutoZone Duralast sensors are not any good. Maybe they can not switch fast enough? I put in a new computer, same old problem. Now, the only thing that has not been switched out is the ePROM in the computer since I can not get one. I could try calling the junk yards, what little are left around here after the new EPA regulations (which were needed because the local yards were just dumping loads of oil and other fluids on the ground which does go to the water supply).

I wish I had an oscilloscope so I could read the actual pulses coming from the sensors, so I could see if there are missing pulses. I don't know what else to do other than try to locate a used '93 Buick LeSabre ePROM. Do I need one from a 93 LeSabre, or can I get use one from other '93 Buick cars?

I was told that the ePROM was most likely not bad and not causing this problem. So I really don't know what to do. I was thinking of taking the new crank sensor off and putting the old one back on and see what happens. The only thing I can think of is the Duralast sensor can not switch fast enough and is setting the Code 18. However, others are using the Duralast sensors without problems. The only way to tell if the sensor is dropping pulses is to use an oscilloscope and I don't own one and can not afford to buy one. I thought about getting one of the cheap ($30) interfaces to turn an old computer into an oscilloscope so I could see what is happening at the crank sensor as the engine is running. The Code 18 sets less than a minute after starting the car.

I sent a detail letter to a local GM dealership but of course they did not reply. There is a college nearby (30 miles) with an Automotive Systems Technology course and I contacted the head of the course to see if they would like a real world challenge for their students. No reply.

I am lost at this point.

Here is the GM shop manual pages for this problem in case it can help someone to give me some directions to take.

where are you at, ive got a couple scopes around here, but its not something that i would let someone borrow. if you were close i would help you see whats going on. if you dont have any luck call some different auto programs, or maybe someone who fixes electronics will know someone local who can help you.

According to google maps, 657 mi, 11 hours 39 mins, not exactly a skip and hop. Thanks for the offer. I have checked on ebay a few times but the bidding always goes up above what I can afford and even a small scope is not cheap to ship. It could be the connections between the connectors and the computer but no way to really test without a breakout box. I took each wire of the wiring harness at the computer connectors and gave each a gentle tug (that is a lot of wires) to see if one was back out when plugged in. All the wires are fixed in the connector as they should be. A strong magnifying lens showed no broken connectors. The same for the ICM connector. Ohm tests show everything OK.

Yet, I get this Code 18. While the rough running engine could be caused by other conditions, I need to fix this Code 18 problem. It must be significant. It sets the CEL and the CEL stays lit as long as the engine is running.

i dont know how these things mount but is there anyway the one of the sensors could be at a different distance from the ring? that can change what the computer sees, like when the abs wheel sensor gets a little dirt or salt in the hole it wont work properly.

On the '93, the crank sensor is fixed in position. When I decided to check the timing chain to see if it could have jumped and causing this error (which I don't think it will even if it does jump) I decided to go ahead and replace the Duralast sensor out with another one since it was under warranty. I checked the harmonic balancer and all the vanes seemed to be the same, no bent ones. Plus, the vane rings are riveted to the crank pulley and there is no way for them to shift in position. I also took the time to clean the vanes as well. It probably is a wiring issue but dang if I can seem to find it. My guess that the Duralast sensor can not switch on and off fast enough is a viable one; however, probably not very likely. Of course it is just misses one pulse each revolution, I think it would set the code 18 according to the instructions I posted above (if one can read them, the pages are thin and I really needed to put a backer behind them for a proper scan)

The way the ICM is made there is no easy way to test without a breakout box. I read on one site to use a wire piercing probe that pokes through the wire to take readings.

I decided I had put off returning to this problem long enough. Today I decided to check the wires from the ICM to the connector at the crank sensor. Now, If I had been smart; which evidently I am not, I would have done this when I had the front of the engine tore down, and had the front motor mount (t-bone mount) out of the way. Today I decided to check the wiring and I had to take the alternator off, and the coil packs and the ICM mounting bracket and it was still a PITA to get the connector up behind the motor mount to where I could take it out of the loom (which has become brittle itself). I noticed that one of the wires looked as if it had overheated and the insulation had become blackened. When I started picking at the insulation it was brittle and pieces would flick off. I don't know if this is the cause of my problem or not. All static tests came back positive but it could be that in running, there was enough vibration to cause a temporary short or cross connection to occur. The insulation at the connector where the wires bend was also cracked. I will know when I repair the wires. I looked at a new connector at a local shop and they want $60.00 for a pigtail connector for the crank sensor. What the heck?

My question is what caused this to happen? the sync wire 3x, and the 18 x wire had gotten hot enough to melt together. The insulation was cracked on the positive power feed to the sensor. Maybe the first crank sensor I installed shorted out. That is not a good thought to have considering the second on is the same brand name.