HOW TO REMOVE THE INTAKE MANIFOLD GASKETS FROM A 1995-98 CADILLAC NORTHSTAR ENGINE.
I promised I would detail my procedure of removing the intake manifold gaskets from a 1995-99 Northstar with lots of pictures so here it is. First though, let me star by saying this is a really freakin easy fix, total time excluding cleaning time 30 min to disconnect the necessary hardware and get the manifold up and out of the way, cleaning time 1.5 hours and 10 min to put it back together. Now you may ask why so long to clean everything but we'll get to that later.
Step 1: remove vanity cover Step 2: remove spark plugs from front bank Step 3: before you go any further you should disconnect the negative lead to the battery Step 4: remove PCV crossover pipe Step 5: remove EGR and crankcase ventilation pipe at the throttle body spacer Step 6: Disconnect the fuel rail ground wire at the rear cylinder head by removing the retaining nut Step 7: remove the purge solenoid harness by removing the reatining bolt and disconnect from the intake manifold Step 8: Disconnect the throttle body heater hose from the water crossover. CAUTION this will result in a fair amount of coolant release I would recommend you have shop towels underneath or a tray on the floor, oh and this is a pain in the a$$ to get off. I used pliers, moved the clamp off of the hose inlet onto the more flexible portion of the hose and worked the hose off with pliers. This doesn't have to be done to get to the gaskets but it will give you more space as this hose is very short and limits how much clearance you're going to get. Step 9: remove the throttle body heater outlet hose from the coolant overflow pipe. You can remove it from the throttlebody as well however the hose is flexible and can simply be moved out of the way. Use shop towels to catch any runoff, there isn't nearly as much as the throttle body heater inlet and the tube comes off quite easily. Now it's time to clean :) Here is where I got sidetracked for about 30 min. I decided to clean my throttlebody since I had to take the airfilter hose and ducting to the throttle body off anyway to get to that throttle body heater hose. Therefore you will also get to see how to clean your throttle body!
Step 1: remove airbox hose and throttle body duct Step 2: open throttle body (it is possible to use something (I used a wrench) to prop open the throttle body valve allowing easier access. That black lip at the bottom is all carbon buildup, and it was pretty thick which was why the valve would stick whenever I started the car becuse it would warm up and become gummy and then cool and solidify effectivley gluing the valve shut. If you want to do a really thorough job cleaning the backside of the throttle body you can remove it from the spacer but you will need to replace the gasket (which I did not have so I did not bother doing). Ok, now that that's done it's back to the INTAKE MANIFOLD
Step 10: unbolt all 10 retaining bolts from the intake manifold (6 are flat grey hexbolts, the other 4 are the tall black posts that the vanity cover sits on), lift upward, and prop up, the unit weighs maybe 2 lbs, and is really easy to move. I did not disconnect the injector assembly or fuel lines because they are flexible to a degree (I still have the plastic fuel rail installed on this car). This allowed me to pick the manifold up as far as the fuel lines allowed me to go and then insert a bar underneath the manifold across the two camshaft valve covers. The gaskets then simply pop off. Step 11: clean the surfaces with carb cleaner until shiny and clean. I was amazed just how much oil, grime, dirt, small nest from a mouse, leaves, grass, etc had found its way down mostly into the valley where the starter motor is (the large grey cylinder right there) but there was alot of oil in and around the gasket locations which can be seen in any of the intake pictures. I used an industrial vaccuum to get the leaves, grass, pebels, and sand out of the valley and around the intakes. I had to carb clean this about 10 times to get the oilrings off and the grime out of the little pockets. The picture below is not cleaned, it was sitting with carb cleaner on it. Step 12: replace old gaskets, reseat manifold, screw down torque each bolt to 89 in.lb. This step was too hard and boring to take a picture of so I just put another dirty picture up. OLD GASKETS: here's the fun part, I couldn't find anything blatantly wrong with the gaskets, no cracks, warping, etc. However what I found later was interesting and explaind everything. I'll let you see if you can find it in the next couple of pictures, it's hard to spot but I was shocked when I saw it, and I went back to the intake and sure enough the evidence fit the bill...
Lets call this pic 1 pic 2 (sorry this is out of focus, the camera wasn't meant to be held 4 inches away) pic 3 pic 4 pic 5 (study closely) Look at pic 5 again, look at the dark band right above the light colored soft gasket part. It's all marred and scratched up. As it turns out this was the gasket from the back bank and 3 of the intakes looked like this. What I think happened was that due to the manifold bolts not being torqued down enough (I know this because I could loosen them by hand the first time when i was trying out socket sizes) let grime, sand, etc between the gasket and intake and as the manifold was jolted around from driving and the effects of thermal cycling rubbed back and forth scaring the gasket and further loosening it eventually enough so that when cold, it would allow air between the seal.
The end result was that when I fired the car up with the engine at ambient temp (had sat for over 12 hours), it fired right up and was smooth without skipping or missing like it has been doing. Overall I am pleased with how easy the fix was and I learned alot about how magnificantly this engine is layed out. From an engineering standpoint it's beautiful, from a mechanics a bit of a nightmare. I happen to be an engineer so it was pleasant and very simple to understand the rationale behind the layout.
