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Thanks to Padgett for this information. - www.6007.us

Padgett (C) 2002-2009

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.

Note: if the SES or Check Engine light does not come on when the engine starts and stays on as long as the engine is running e.g. goes out sometimes or comes on a few minutes later, it is probably not the interrupter (magnet) - they do not heal.

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



Fig. 2 View of good but dirty interrupter. Roughly circular and sticks out from the sprocket.
Might want to check this first to see if it is really your problem.

To repair, 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. 3a: Aftermarket cam magnet (Niehoff DR1403 from promo.)   Fig 3b: Diagram of Cam Magnet (interrupter) modification.

Fig 3c: Ground Down Cam Magnet on Magnetic Pickup Tool

Next remove timing belt (suggest also removing the water pump pulley) and the cam sensor. 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. May need a mirror. Is usually very close to TDC.

 

Fig. 4a Missing Magnet - plastic remnants still in hole        Fig 4b: Cleaned hole - use alcohol or brake cleaner to get really clean. Dark area is beyond edge of cam behind 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.

Fig 5: New Cam Magnet inserted in sprocket with JB Weld

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 in late 2002 and have had no problem since.

Valuable comments from Paul W.

"I removed the "brim" by placing the interrupter in the chuck of a drill press and closing the chuck firmly by hand only; I then had the drill run at approximately 300 rpm and held a file against the brim until it no longer protruded beyond the diameter of the main magnet enclosure; I did it this way because it was easy and I was afraid I might cut too much off and compromise the magnet's encapsulant.

Next, I found good control during insertion of the interrupter by not using a 1/4" drive 1/2 or 13mm socket but using only the extention which had a rather flat end (the female end of the extention will not work as the contact end has to be solid); the magnet held firmly and I was able to slide it sideways and off to release."

Note(app-2009): Harbor Freight Magnetic Pick-Up tool works even better.

Also I put a fresh flat file in a vise and with the new magnet protruding from a 5/8" socket could slide the interrupter across the file and remove the brim quickly and cleanly.

Step by step replacement

1) Start as if you were going to replace the water pump except do not take any water pump bolts out.
- remove serpentine belt, water pump pulley, and any resovoirs that block access.
2) Disconnect wire from cam sensor
3) Remove cam sensor bolt
4) Remove can sensor - Will probably need a mirror to see in hole
5) Rotate engine until either interrupter or hole where interrupter once was in cam sprocket is visible
- rotate either with key off and out with breaker bar on crank bolt (easier with plugs removed)
- or by bumping starter with plug wires disconnected (hard to stop in right place)
6) If interrupter is missing then continue else check sensor for continuity
7) Remove any remnants (can use an awl) and clean the hole in the sprocket and surrounding area *thoroughly*
8) Proceed as in article to modify new interrupter and JB Weld in place
9) Allow to dry overnight before replacing sensor
10) Replace everything you took off

Interrupter Part Numbers: GM p/n - 25530386, Niehoff - DR1403, Borg-Warner (now BWD) - CSS3

Weasel words: The process described above worked for me on my car but may not work on every car. A lot has to do with how clean you get the magnet and how well the hole is cleaned out. I do not speak for GM and they do not speak for me. Your mileage may vary. Notary sojack y'all.

contents copyright Padgett 2002-2009 except where noted.

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