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Cadillac Tech Tips - How to fix it Discussion, 2000+ Northstar Plenum Replacement steps in Item Specific Cadillac Discussion; Before you start this procedure you NEED to study this entire thread !!! Both pages............from the beginning. Some of the ...
  1. #16
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 2000+ Northstar Plenum Duct Replacement steps

    Before you start this procedure you NEED to study this entire thread !!! Both pages............from the beginning.

    Some of the fittings and vacuum lines - EVAP and PCV are two - are different from 2000 to 2001 to 2002. Close, but different. Back about 20 pictures the orange plug "doohickey" is the MAP sensor - it sends an inverse vacuum signal (negative pressure) to the PCM. This picture series has a rattle-type PCV valve. Later engines do not - the dirty air pipe slips over a permanent fitting with a fixed orifice inside. Remember that the 3 long bolts through the throttlebody are what secures the plenum metal flange - they must be removed before the manifold will come off the engine. The manifold bolts (10) get torqued to 89 in/lb - only about 7.5 ft/lb, so be careful. Break a manifold bolt boss and you'll be looking for another manifold. Smear a bit of engine oil around each injector O-ring before you drop the fuel rail back in. It makes life a lot easier. Double check all the injector electrical connectors.
    eyeu81, eyeu81, Amitayus and 3 others like this.

  2. #17
    DougC..'s Avatar
    DougC.. is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Replacement steps

    Is the tear a common problem for newer than 2002 northstar engines? I have a terrible idle, (shakes the car) and misfires. Noticed that the intake bolts were loose the other day, one was almost all the way backed out.

  3. #18
    songbird is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Duct Replacement steps

    wow... thanks for all the time and knowledge...just bought my caddy and thinking I will have to do this....the pics were awesome... I'm also a shadetree mech... but kind of got lost about all those connections and hoses...
    I just want to replace my plenum gasket... I have cleaned the TB, mass flow, and map sensors... also installed a new cam sensor... the caddy idles a little rough but not bad... I did replace the plugs.. it had bosch in there.. and that made a difference... I have to install a fuel pump and fuel sensor when weather permits...just got the pump today...anyway just wanted to say thanks for the upload... I might be taking pics of replacing fuel pump and filter....this seems to be a common problem also...
    thanks again,
    Craig

  4. #19
    LymanSS is offline Cadillac Owners Fanatic
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    Re: 2000+ Northstar Plenum Replacement steps

    I did this repair last weekend after procrastinating for ages. Many thanks to those who contributed to this thread, as it was a huge help to have the description and images throughout the process. A couple of notes from my experience (2002 DTS, built in January 2002)

    1. I found it easier to get the fuel rail up and out of the way if I first removed all of the injector cabling. Pull up on the slider and pinch to release the connector.
    2. I had a few extra vacuum lines running around, and a handful of differences from the photos posted earlier in the thread. If you've got an '02 DTS, watch out for these slight differences, but don't let them throw you off.
    3. I suggest looking for hard vacuum lines and removing them early on, especially if it's cold out. I was working in fairly cold weather which apparently causes the structural integrity of the vacuum lines to resemble that of a potato chip. I snapped two of them without even realizing it. Fortunately a trip to the local Autozone yielded some flexible vacuum line that fit the same connectors. Don't bother trying to fix the old stuff. I tried super glue and welding but had no luck.
    4. If you are the type of person who hates re-installing a filthy part, plan some extra time for cleaning the manifold, throttle body and runners. I didn't have time for this, and it's going to bug me FOREVER, knowing how much black crud is caked in there.


    Scott

  5. #20
    cosmictrucker's Avatar
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    Re: 2000+ Northstar Plenum Replacement steps

    Well....my 02 DeVille is now in need of a plenum gasket replacement. The car has been acting up and not idling it's normal rock solid smoothness. I also had noticed that the trans was clunking when I went from drive to park, something it never did in the past. I guess that was due to the higher than normal idle speed. The car was idling so poorly today after driving home I popped the hood while the engine was running and clearly heard the vacuum leak around the plenum.
    I've been putting off replacing the water pump, so I guess that will be on the list while I'm working under the hood. The serpentine pulley's are making some noise too, and I'm really not looking forward to that job due to the tight space.

    Any additional tips not already covered will be appreciated. such as any parts needed that may not be obvious.

    Thanks

  6. #21
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    Re: 2000+ Northstar Plenum Replacement steps

    Great tutorial! Can the split in the boot cause a higher than normal idle speed without setting any codes?

  7. #22
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 2000+ Northstar Plenum Replacement steps

    Maybe ................ as can happen with any other small vacuum leak - begin by checking all the vacuum lines to/from the intake manifold and throttlebody. (Kicker is: The plenum is usually not a small vacuum leak)

    Vacuum diagram for your engine (If not exact, very close) in my albums - Community tab, Albums, the red Seville. 2 albums, 6 pages, 113 pictures/diagrams.

  8. #23
    monty_n_philly is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Replacement steps

    How do I findout if my Plenum is bad and does need replaced? 59k on 03. The car was serviced (oil changes and all) at certified Cadillac Dealer. Car came with 9 pages of updates... so they did everything they could. I don't hear any sucking noise, but I might not know what I am looking for.... THanks

  9. #24
    Ranger's Avatar
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    Re: 2000+ Northstar Plenum Replacement steps

    A ripped plenum duct will set a P0171 & P0174 code.

  10. #25
    monty_n_philly is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Replacement steps

    Amazing thread... I did this on my own car in my drive way.. Thanks Ghostsoldier.... those pics were perfect...

  11. #26
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    Re: 2000+ Northstar Plenum Replacement steps

    No problem, Monty...I'm glad to be able to give back here on this amazing forum.
    Rob

  12. #27
    redfishsc is offline Cadillac Owners Fanatic
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    Re: 2000+ Northstar Plenum Replacement steps

    Did this swap tonight, car now runs and idles great!

    On my 2003 DHS, the fuel rails were held in place by a bolt sitting sideways, on the front fuel rails between the throttle body and front radiator shroud (10mm nut.... the bolt is a fixed part of a bracket), you just pop the nut off and wiggle the fixed bolt loose. Very easy to access.


    I ordered the Dorman plenum/gaskets from RockAuto, and the blue gaskets were NOT useable. They were the right "size/shape" but they would not seat firmly into the recess. Even if you managed to put them in and keep them there, they'd start falling out when you shimmied the intake back into place.

    I tried ONE of them, and since it didn't seat, I didn't touch the old gaskets. I left them in place. Cleaned them with WD40, cleaned the aluminum head where the intake bolts on with carb cleaner so that it was shiny again, and seems to be fine.

  13. #28
    Kelvin Averbuch is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Replacement steps

    What a great article! My 2003 Seville had high idle, felt like cruise control was on. 1. Removed and cleaned IAC valve: no difference. 2. Removed and replaced TPS valve: no difference. 3. Replaced plenum connector (with 2" tear at the bottom) per this article, and replaced torn vacuum connector at other end of the intake. Now the idle is perfect and gas mileage around town increased from 16.5 mpg to about 22 mpg. Thank you very much.

  14. #29
    nphoenix is offline Cadillac Owners Member
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    Re: 2000+ Northstar Plenum Duct Replacement steps

    I want to thank ghostsoldier and others. I compelted the job on my 04 deville today. I used the Dorman part from rockauto 911010 (911-010) for $15.40. It came with the blue gaskets and they did seat fine in the channels for install. On an 04 deville the fuel rail clamp is a #10 nut and not under a wire harness. Also on the passenger end of the manifold the hose that goes to the pcv(?) valve was disintegrated at the 90 degree elbow so i needed to replace that too.

  15. #30
    Closet Boy's Avatar
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    Re: 2000+ Northstar Plenum Replacement steps

    Excellent thread. Within a few days, I'm about to take on this challenge. I too bought the Dorman from RockAuto.com.

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