Facing the task of UIM/LIM replacement concerns me because of my inexperience working on engines, so when I wrote "dumb people" in the title I meant REALLY dumb people (me).

This tech info article http://www.bonnevilleclub.com/forum/...e=article&k=38is very helpful, but I would like to clarify some points based on what I have read on the site from various places. I also think the article assumes a higher level of knowledge than I currently possess.

This diary was VERY helpful, but may have given me a false impression of the ease of this repair. http://www.bonnevilleclub.com/forum/...86&highlight=A so here'* what I think I have to do for UIM/LIM repair on a 96 SSE / L36:

1. Order APN kit for UIM and LIM gasket set GM 89017816.
2. Either order or have machined a new stovepipe. Order new elbow , make sure o-rings aren't flawed.
3. Order new 180 thermostat/seal/gasket (agrazela gave me a good list of what I might need at http://www.bonnevilleclub.com/forum/...ic.php?t=71440
4. Drain oil and coolant
5. Disassemble UIM and LIM. Remove alternator for easy access. In my case also remove valve cover since it is also leaking.
6. Clean, according to Bill Buttermore "use a tungsten carbide gasket scraper to clean the crud off gasket sealing surfaces, finishing with brake parts cleaner to degrease"
7. Reassemble with new gaskets in place and cleaned parts.
7a. There was a thread once about the importance of how many pounds of torque...I couldn't find that thread. Use BLUE locktight.
8. Refill oil and coolant (remind me: Are air bubbles/pockets an issue here and how do you avoid them if so? )
9. Start car while praying. Watch for leaks.

Where in this list is
A) an important point missing
-or-
B) places where an inexperienced person might make a small but fatal mistake.

I think step 7 and 7a above worries me the most and that'* where (B) is important

I really appreciate all the advice that will flow. My GXP payment forces me to repair the SSE myself. Such is life.
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You will not need to do anything with a stovepipe. Unless your LIM was updated, the APN reduced diameter stovepipe will fit right into the .750" bore of your '96 where you will remove the stock pipe.

Torque spec'* for the LIM are 11 ft-lb; for the UIM, 89 in-lb (7.5 ft-lb)

Buy a Chilton'* 28200 for $20. It will outline the procedure for you and provide drawings of bolt tightening sequences. (These are usually start at center and work your way out to the ends going side to side so that the part is pulled down evenly without getting cocked. Typically, you hand tighten in sequence, then once around at the specified value, then once again.)

When I do these, I remove the tensioner assembly as well as the alternator. On your '96 I think there will be a big o-ring where the tensioner nipple pushes into the water pump housing. You may want to replace that o-ring, too. I also spray the exhaust crossover bolts with Power Blaster penetrating oil, and remove the crossover pipe. This gives great access for removing the throttle body. I put the crossover bolts back on with anti-seize. It is a good idea to clean the throttle body while you have the thing off. I use a scraper tool called a "super scraper." It costs $20 and has a tungsten carbide edge about 3/16" square that is very sharp. I have used mine for about 10 years and it is still sharp. I also use a razor blade scraper that takes single-edge razor blades to scrape off glued on gaskets. I don't like to use abrasive gasket removers on engine parts where the abrasive dust can end up getting into the crankcase or moving parts. After removing the LIM, cover the crankcase valley with clean rags when you scrape the heads so the crud does not fall into the engine. All of this takes time. I do not hurry when I do this kind of work. It usually takes me 5 or 6 hours to get one done.

The coolant fill procedure is given in Techinfo article 100. Go to Techinfo, Mechanical, Engine, and you will find it.

Great, great, great. I am going to get the Chilton'* as well. THanks for the help.

Good work, Bill! You answered all the questions quickly and efficiently. Gold Star!

Two Bonnies, follow Bill'* lead and you won't go wrong.

I think it was. The UIM was replaced in 2001 under extended warranty at the Pontiac dealership. The casing has a manufacture date of 12/20/00. How would I tell if they also replaced the LIM at that time?

After 1999, dealers replaced a lot of older LIMs when L36s came in with internal coolant leaks, especially if the UIM was found to be perforated at the EGR bore around the hot stovepipe. They did this because GM changed the stovepipe bore and stovepipe from .750" in the older LIMs to .625" in the newer ones in an attempt to address the problem they knew they had with the hot stovepipe deteriorating the plastic bore in the UIM. They would replace a $200+ component just to get that smaller stovepipe. I don't know of any external markings on the LIM that would reveal whether the pipe is .750" or .625". You will be able to tell as soon as you remove the throttle body and look into the UIM. The stovepipe is visible then. The older, .750" pipe sits right against the plastic, while the .625" pipe will have a gap of about .065". I will go examine my spare LIM to see if the bore diameter can be determined by removing the corrugated stainless pipe from the outside of the LIM at the base of the stovepipe. I would think it would be very difficult to determine when all the parts are assembled.

If you do have a newer LIM with a .625" pipe and bore, you have two choices. You can just run the stock GM .625" pipe which will give you an insulating gap of about .065" between the hot pipe and the metal heat shield in the APN UIM. This is not a bad fix. But you can make a much better fix by turning the base of the APN pipe (which has a .750" outside diameter on its base) to .625" on a lathe. Add a small chamfer to help get started in the bore hole. By using the APN pipe instead of the stock GM pipe, you will increase the insulating gap between the pipe and the shield from .065" to about .125".

The horizontal bore into the base of the vertical stovepipe bore in the 95-98 LIM measures .651" I don't know if this bore size was changed in the newer 99+ LIM when the vertical stovepipe bore was changed from .750" to .625". But, I will see if I can find that information. If so, it would provide a relatively easy way to infer the stovepipe size without removing the throttle body. With the throttle body in place, it would be very hard to determine whether the pipe is a .625" or a .750".

[edit: With the exterior corrugated EGR pipe removed, I took the measurement from the vertical surface of the LIM on the driver'* side in to the base of the stock .750" stovepipe. This was approximately .850". I used the depth gauge end of my electronic calipers at the 12:00 O'Clock position of the hole. The distance in to the base of the smaller, .625" stovepipe should be greater by .063". So, if you remove the corrugated pipe from the LIM (10mm head bolt) and get a measurement around .910 into the stovepipe, you have the new LIM and stovepipe; if it is around .850", you have the old one. A little tread depth gauge may work better in the tight space when the LIM is in the car.]

Some additional steps:
4a) remove ignition wires from spark plugs and set aside
4b) carefully unhook all wiring harnesses, vacuum lines and sensor connectors in vicinity of UIM, fuel rail and LIM (color or number code wires and vac lines with tape flags if necessary) and move out of the way
4c) unhook harness wiring from fuel injectors, and remove fuel rail from atop UIM; leaving flexible fuel lines attached, set rail out of the way (turn it over and perch it "injectors up" at the base of your windshield--tie it up there with a strap or something so it doesn't come crashing down on you)

7a) torque specs here:
http://www.bonnevilleclub.com/forum/...281&highlight=

7b) reconnect all the stuff you disconnected in 4a0 through 4c), then double check it, then triple check it (inspect your injector o-rings before reinstalling fuel rail)

good idea. I also intend to take digital pics at every step. My biggest single problem is getting to a point where I say "now where the h*** does that thingy go?"

The Chilton is ordered.

It might be cool for me to live blog this - if I had a webcam. My home office is five feet from the L36.

I have done this before... for more info check out this thread... It happened about a year ago and the car is still going strong. I need to post a couple of updates that I promised too... Best of luck!
http://www.bonnevilleclub.com/forum/...&highlight=nim