I have a 2001 Pontiac Firebird with about 108,000 miles on it. I have been loosing coolant slowly for a while now. Just pressure tested the cooling system at 15psi. and would loose about a pound of pressure every couple of min. Problem is, I cannot see any coolant leaking anywhere!!! Everything is bone dry. No coolant in oil either. Was thinnking intake manifold gasket(*). Only clue I found is taking out PCV valve, would see a little moisture mixed in with oil residue on valve. Didn't know if it was condensation or coolant mixing in. Anyone with other ideas???? Car runs like a champ. Don't think it is head gasket. Planning on replaceing Radiator, water pump, hoses and intake manifold this weekend.

Intake manifold gasket, water pump and hairline crack in molded plastic portion of radiator would be places I would look. As you mentioned, no sign of missing coolant is surprising. Sometimes small coolant leaks look like oil leaks as the small amount of coolant mixes with oil and dirt residue. The pressure test should show you the problem sooner or later.

Well after getting every thing apart this weekend, I found minor failures in both upper and lowwer intakes. Gonna get her back together this week. Question though, do I need to replace o-rings on the fuel injectors? It sceems like thier isn't alot that holds them in and seals them. What is the best way to clean out the intakes? How do you clean off old gastket from the heads without getting crap down into the engine?

Here is a decent write-up that will answer most of your questions, graphically.

http://www.handymanlyness.com/archiv..._99_Jimmy.html


If you buy a fel pro kit, they often come with all the items you need to include fuel line washers. Each engine is different, so you will have to check the parts included. rockauto.com is a good source for the intake manifold gasket kits.

Well, after Christmas I put in an new UIM and LIM gastket(*). While I was in the general area, I put in new lifters as well.
Both UIM and LIM had minor failures in them. The upper failed where a couple of O-rings were right by the throttle body. The O-rings were almost turning to dust. The lower failed on the left bank by the middle cyl. intake. In both areas found the (greenish sludge). Cleaned up everything really well. The throttle body butterfly on the inside was very dirty. Probrably from where EGR comes into intake in that area.
Car now runs even better!!!!! Very happy I did this myself!!! Thanks to all who helped!!!

Congrats, it feels good doing the work yourself! I've learned a lot in my few years on the forum and tinkering around in my own shop.