I'm getting my '91 ETC ready for the dreaded California smog test and I have a SES light one for
26 - Shorted TPS Circuit
41- Cam Senser circuit
How do I go about fixing these?

http://i106.photobucket.com/albums/m280/merc892003/E026.jpg

http://i106.photobucket.com/albums/m280/merc892003/E026T.jpg

http://i106.photobucket.com/albums/m280/merc892003/E041.jpg

http://i106.photobucket.com/albums/m280/merc892003/E041T.jpg

The cam sensor is not too hard to swap out yourself. I've done it a couple of times, and I'm no Mr. Goodwrench. If you go a parts store like NAPA, you might have to ask for the Hall Effect switch (another name for camshaft position sensor).

You'll need to remove the distributor cap. Use some strips of masking tape to label each of the spark plug wires. You don't need to know which wire goes to which spark plug. Just number them in sequence going around the distributor cap so you connect the right plug wire in the same place it was before. Remove the rotor button and you should see the switch underneath the rotor. Access to the mounting nuts is not the best. If you can get a 1/4" wrench with a slight angle offset, it will be easier.

When you have the switch out, be careful unplugging it and plugging the new one back in. Considering the age of the connectors, the plastic may be brittle and could break easily. Once you have it connected, you have the fun task of putting the mounting nuts back in. Just take your time and be patient. The last time I did this back in January, it took about 30-40 minutes to do the swap. I've done it before, so that made it a little easier.

While you have the distributor cap off, this is also a good time to replace the ignition control module. That one's easy to get to, and the part itself is ~$30. Again, be careful with the plastic connectors. I had an intermittent stalling problem with my '91 DeVille, and replacing the module cured the problem. Even if you're not having that problem with your car, it's a good idea for preventive maintenance.

I'm afraid I can't help you with the TPS. But good luck if you try swapping out the cam sensor. If you have more questions, post them here or shoot me a PM, and I'll try to help. There are some other more knowledgeable 4.9 people here (HUF is one that comes to mind) who might have some advice for you as well.

Sevillian; Thanks for the trouble tree, I do have a FSM but some times its easyer to understand in human.
Gdwriter, so confirmed for sure the distributor doesn't need to come out?

Gdwriter, so confirmed for sure the distributor doesn't need to come out?No, you don't need to remove the distributor. As I mentioned before, access to the mounting nuts is difficult, but if I can do it (and I've done it twice), I think just about anybody can.

If you remove the airbox, you can pull the distributor cap without removing the wires. I use a 1/4" nut driver for the dist bolts. Use a 1/4" box end wrench to get the 2 cam sensor bolts out. If you have a DVM you can check it then. The test procedures are a little easier to understand in the Haynes book. Beware the cam sensor is outrageously expensive (~$100) !!