1991 Bonneville LE has 41 code but runs fine. Changed the following so far cam sensor, ECU, ignition module/coil pack, plugs, wires, verified the cam magnet is in place. Used a flow chart to trouble shoot but it keeps going to ignition module. I put 2 new ones int. I checked wires for continuity. Only thing I didn't replace is the crank sensor. Would the car still run if this was bad? Anyone have good suggestion. Frustrated with this project car for my son.

The car only uses the cam sensor as reference for fuel injection timing, namely it references when Cylinder #1 passes by. Otherwise, it just assumes #1 is the next to fire at startup, and sets the code. This essentially means that there is a 1 in 6 chance that the injection timing is correct. This can cause drive-ability issues depending on how far off it is, and would likely cause issues perceived to be intermittent.

If you are dead sure about wiring, and are positive there is not a connectivity issue at the PCM, or the fire wall, you may want to confirm that the magnet on the cam shaft is still magnetic. There was one instance I can recall that someone had similar issues, with similar results, and he discovered that despite the magnet being intact, it had essentially turned to goo, and became really weak. His issue was also not completely consistent in setting the code as well.

I assume codes were cleared and everything as well each check, correct? I have had some blond moments in my day when it came to old codes.

And to further clarify, the computer does pretty much all of the running from the crank sensor, and a faulty crank sensor will cause the car to not run at all, especially when restarting after fully warmed up.

Thanks for your input. Magnet is still on cam and held a paper clip to it. It is still magnetic. The flow chart I am following shows it is actually reading it because I had to bump the key to turn it past the magnet to change from zero volts to a reading. I had a mechanic at work tell me he had a different car that threw the same code and it was another sensor. Mass Air flow or something. Another car would still run but wires were ccompletely corroded off the crank sensor. So tonight we pull off the crank pulley and replace the crank sensor. Hopefully that resolves it.

I looked it up on this site:
GM 91 3.8L VIN C ? OBD Trouble Codes

And found this:
I find myself leaning towards an intermittent failure. How quickly does the code set after cleared? I am betting it is more than 5 seconds in. Code definitions for other years indicate 2 seconds for this figure. To not be noticing any drive-ability issues, I suspect it is getting the signal at some point, but it'* just dropping out.

Hopefully you can get it tracked down at least, and I am curious how it turns out.

Also be warned, that the bolts needed to pull a 3.8 balancer are not usually included in the standard puller kit for most engines. They are a specific metric thread pattern (can't remember what). Sometimes bolts are included that are close, and may get some bite, but there is a high risk of stripping the puller holes if they don't get enough bite to pull the pulley off.

Also the LN3 has an adjustable CPS. You don't necessarily need an alignment tool, but you will need to take care when reinstalling to ensure proper alignment.

Also make sure you are prepared with the tools to get the balencer bolt out. That is probably the hardest bolt in the whole car to get out. I believe torque instructions on it are 130+ ft lbs, plus TTY, plus threadlocker, plus 25 years of service, to give you some idea of what you are facing.

Crank sensor changed. You were correct on the bolts not fitting that came with balancer. Luckily video on you tube gave me the correct size 1/4-28 fine thread x 3.5" long. My son actually was able to remove balancer with trick he saw using starter to bump it loose. He did a good job but it did not fix the code. I am glad he changed the sensor as it had a lot of rust flakes stuck to magnet on the sensor as well. I am going to recheck the wiring since all sensors have been changed. Only thing not placed is the magnet on cam. I know it could hold a paper clip straight out but is that enough strength. We will keep at it hopefully report what we find.

Just something to check, is there a coolant level sensor on any of these cars? I had a '90 Lumina with a 3.1 that would idle, but sputtered and died when you tried to drive it. Turned out the coolant level sensor in the radiator had gone bad and was cutting reference voltage to the TPS and other sensors from the required 5V to 2.8V... Garbage in, garbage out. Disconnected the coolant level sensor in the radiator and the car ran fine. Didn't throw a code, but just something to check, since the 3.1 and 3800'* control systems are different. Hope that helps.