First I want to say Thanks for all the help and tips from this Great Board !!!!

This is how I did this procedure...

1) Removed gas cap

2) Pop hood remove Top cover and bleed off pressure from fuel rail pressure relief valve

3) Take off top of air box and air tube closest to tb, unplug maf plug

4) Just loosen the 10mm nut that holds fuel lines down and undo lines from the black clip on top

5) Unclamp the top line on the coolant jug (a little might come out) Lay it to the side

6) In front just unhook one vacume line and unplug the plug going into coil pack

7) In back just unhook the vacume lines that are in the way (I think it was 4 or 5 of them) and unplug the plug going to that coil pack

8) Take the 4 10mm bolts out that hold the fuel rails down

9) Carefully pull up on the fuel rails evenly, they will all pop out together, pull them straight up together you'll have to wigle it around a little but you can get enuff room to work

10) Take the 10 10mm bolts out of the manifold

11) Loosen the plenum bolt (The strap clamp) there are also 3 10mm bolts that hols the plenum in. You'll see them from driver side, pretty easy to get to

12) Hold the fuel rails up out of the way and start from passanger side and lift the manifold up and out

13) Turn manifold over replace all 8 Blue gaskets (most local parts stores have these $15-$20 for a set of 8 )

14) Take off old plenum ( I used a big screwdriver and pryed up around the sides)

15) Put your $30 new plenum on (the same way the old one came off)

16) I took my shop vac and vacumed out everything so nothing would fall in engine, then just wiped it down with old shirt rag

17) Hold fuel rails back up and drop the manifold back into its home

18) Reasemble everything you just did. On the manifold bolts just start in the middle and work your way around, don't tighten till there all hand tight.

Thats pretty much it. Of course inspect everything as you go.

When i did this job all 10 of my manifold bolts were loose like all of them were just hand tight. I thought that was crazy..

The whole job took me about an hour and a half. because i have never done this before. Stealership probably can do it under an hour. Started it up and it runs perfect. :highfive:

Hope this helps Thanks for Everything

Good post - the factory torque on those manifold bolts is light: 89 in/lb., or 5.5 ft/lb.

Just curious - can't you leave the injectors and fuel rail attached to the manifold and R and R it as an assembly? You can on a '97 - maybe 2000+ is different?

Thanks for the rundown! Looks like I'll be doing mine next weekend, if the parts arrive...

Thanks for the post and pictures. I have the parts an will attempt this tonight. After throwing money into O2 sensors and MAF sensor, I found the quick test (spraying at the bottom of the plenum) with carb cleaner fixed the problem. Looking forward to a smooth running engine with no codes.

Thanks for the nice writeup. I did this last night, about 1.5 hours. No problems, purrs beautifully now.

Went to bed and remembered I forgot to tighten the Radiator fill cap. Went down to tighten it and thought I would check the level. Black oil in the overflow - not good.

Anyway, one problem solved, on to the next.

Thanks for the write-up. I did this the other night, roughly 1.5 hours, and the engine is smooth as can be, no codes. Saved me a bunch of time. Nice clear information.

Only issue now is, I noticed oil in the antifreeze. Oh well, on to the next issue.

Thanks, Bill

guys, whats the part number for the plenum?

Plenum: 12555840

here............2000 - 2004 FWD Northstar

Many thanks for this write-up. I thought mine was a MAF sensor, but turned out to just be a crack in the plenum; changed it myself last night and running perfect now. SES light turned off on the way to work this morning. Mine is 02 Deville with 80K miles.

Plenum: 12555840

Thank you very much.

How do you find the part number? I have the parts list, but the engine is not covered. I think its the drawout list, but I dont know where to get it.

Please let me know

I'm halfway done my job at the moment - taking my time, and being careful not to break any plastic..:histeric:

One thing I noticed - my fuel lines are stainless steel, and they're held on by a small bracket just to the right and down off the TB. The rails would not come up out of the way until I managed to get the rail bracket loose, which of course involved removing a clp around a big ol' cable next to the fuel lines, then moving the cable out of the way so I could get a deep-dish socket (13mm?) on the nut holding the rails. Once the rails were loose, I could move them up and out of the way from the other side of the car, and then lifted the manifold out completely.

The plenum was indeed cracked.

Have attached another pic of the fuel rails that I had to jimmy out of the way. Anyone with a newer NS will probably have these rails to work with.

Tomorrow after work I'll be picking up the intake manifold gasket set ( I forgot to order one when I ordered the plenum. Did remember the TB gasket though, which oddly enough cost more than the plenum did.) I'll be putting things back together and hope to finish tomorrow night or Saturday morning if the weather holds.

As others have noted, this is not a difficult job. Getting the steel fuel lines loose took me longer than I thought, because I tried to think my way through removing the manifold without doing it - but there is no way to move the front and rear fuel lines if that bracket isn't loose. And I didn't want to kink any thing...

Update : All back together now. Purrs like a kitten. Smooth idle at just about 725. Had a bit of trouble with the injectors leaking, but that was due to one lost O-ring, and some confusion as to where the O-rings went. When I pulled the rail up, some of the injectors stayed in the manifold, and some came up with the rail. That must have been when I lost one O-ring. Didn't realize it at the time. Leaks galore last night when I started it up but after getting a new O-ring (Box of 2, NAPA, $2.06) and figuring out that the O-rings went on the injector and not up in the rail opening, we got her buttoned back up and started on the first crank. Life is good....I hope...

Thanks for all the information everyone posted. I had this problem and identifying+fixing it was made a lot easier by your posts.

Thank you!

2000 Seville SLS Plenum boot & intake seal replacement.
Getting 0171 & 0174 lean codes and 0101 MAF code.

Stealership wanted $560 & said it was a 4 hr job. Took me 2-1/2 going slow & $73 for parts (8) 12557497 & (1) 12555840

I have to thank all that have contributed to this thread & the regulars that help us weekend warriors all the time. I followed MRVSPITBULLS directions almost to a tee & had zero problems with this repair. And I'm a carpenter with just enough tools to get me in trouble. Working in a stone driveway & not a garage it took me total of 2 1/2 hrs. That was going slow so not to screw up this marvelous piece of engineering called the NORTHSTAR.

The only changes or deviations I made were the following:

1. I blew off the whole area with the air hose prior to any disassembly, hoping to avoid dirt getting where it shouldn't.
2. Move step #5 up to step #2.5. I fought to remove airbox & tube (I'm a carpenter) w/o removing Radiator overflow.
3. Per Jim Hare - loosening the bolt that holds the metal fuel lines near TB helps give you more movement in fuel rails.
4. I found an extra plenum bolt sleeve precariously sitting right next to an intake port when I removed the plenum. I checked to see if I had dropped it. But, I had 10 bolts & 10 sleeves in my hold cup. Sleeve must have come from the factory. Had it fallen into the port while I removed the plenum - I would have never known it & probably would have blown the head apart.
5. Per SUBMARINER409 - oil on injector "O" rings helped reassembly.
6. Not trying to make me seem like a dumby, but was I surprised to find a starter buried under all of this mess!!!!! Should I have replaced it while I was in there? I didn't. Car has 83K on it & never (touch wood) had a starter issue.
7. A good cleaning of all mating surfaces & vacuuming out of all ports before reassembly.

That's about it - pretty uneventful procedure - thank God. Runs smooth & strong again.
And thanks again for all the help this forum provides.