Significant.  Same job as doing a timing chain, if you've ever done that.
Steve

I have a similar problem on my '92 98 T/S and am waiting for spring.  A
buddy of mine wrote
me the following.  I lost the pictures, sorry.   Tom R.

Simple 3800 Cam Magnet Replacement
Getting a constant "code 41" that will not clear and the cam sensor is good
? Odds are the cam magnet (interrupter) has removed itself from the cam
sprocket.

Take to dealer and the quote will be over $500 since the book says the
timing cover must come off .

(Note, if over 100k or the timing chain feels loose if turning the balancer
or an 88 or earlier, it may be a good idea to replace the timing chain and
any worn sprockets/tensioners anyway - always use an 89 or later tensioner -
while off do a water pump also.)

However if pressed for time and money there is a way to replace the
interrupter through the cam sensor hole and you only need to remove one bolt
to do it.

Fig. 1 & 2
Timing cover with sensor in place     Timing cover with sensor removed
Cam sensor is directly under water pump (removed on cover shown)

First get the GM "interrupter" (magnet) p/n - 25530386 grp 0.736 about $14
retail (2002). This is for an 88-90 "C" and 91-92 "L" 3800. You will notice
it is shaped like a top hat with two ears sticking out. The approved factory
"snap in" way is to insert into the cam sprocket from the back until the
ears pop out in the machined recess. The hard part is that the sprocket must
be off the car to do the factory way which is why the timing cover must be
off.

Take the GM interrupter and grind or sand away the brim of the top hat
leaving the cylinder only. Try not to damage the two arms that stick out. Do
not clamp so hard that the plastic breaks either.

Fig. 2: Diagram of Cam Magnet (interrupter) modification.
Next remove timing belt and the cam sensor and rotate the crank until the
magnet (or more likely a hole with some plastic remnants - brim is probably
still there wedged between the cam and the sprocket) is visible. Is usually
very close to TDC.

Fig. 3: View of uncleaned sensor hole and sprocket with only the magnet brim
remaining. Might want to check this first to see if it is really your
problem. Good magnet will be circular and stick out from sprocket.
Using an awl or small screwdriver clean all of the excess/broken plastic &
gunk out of the hole (this is the most time consuming part. Use a mirror so
you are sure to get all of it removed. This is critical. Will be able to see
cam through hole when done. Then clean thoughly with carb cleaner or
something similar that won't leave a residue.

Take a fresh tube pair of JB Weld (that is what was recommended to me & I
have no reason to change) and mix up a batch. Apply liberally around the
sides of the interrupter but leave enough of the top free to hold.

Now comes the tricky part - inserting the ground down and JB Weld coated
interrupter through the sensor hole and into the now clear hole in the cam
sprocket. I used a 1/4 drive socket (forget what size but just larger than
the interrupter diameter, packed the socket so that most of the interrupter
stuck out, and put on a 3" extension - you might want to experiment with
this before mixing the JB Weld ). You need a way to hold the interrupter
tightly enough so it won't fall out while you push it into the through hole
but loosely enough that you can pull the socket back out without the
interrupter coming with it.

Once started in the hole, remove the socket and push it in with your finger
until you feel the arms bottom in the recess (will see what I mean when
cleaning the hole). Make certain it is in far enough to clear the timing
cover (not by much) when the cam rotates. When seated all the way, it will
be.

Finally schmear some more JB weld around the part of the interrupter
sticking out of the sprocket taking care not to get any on the top of the
interrupter - probably not necessary but won't hurt.

Job done, let it dry with the cam sensor off so open to the air for the full
period marked on the JB Weld tube. DO NOT try to start the engine "just to
see" until then.

When completly dry, replace the cam sensor & timing belt and go. .

Like anything else automotive, care and preparation is the key. That said I
did one a year ago and have had no problem since.