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Cadillac 03 DTS
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Discussion Starter #1
My 03 DTS was running like crap last week and I came online to see if you guys had similiar issues with codes P0171 P0174, and discovered that my plenum might be the issue. I purchased the plenum from my local Caddy Stealer for about $ 30 and got the intake gaskets for about $ 17 at Napa ( stealer wanted $ 7 a piece) I removed the fuel rails, intake etc and discovered the plenum had a huge crack on the bottom. I swapped it out put on the new intake gaskets and put her back together, the whole job took about an hour and a half and the car hasnt ran so good in the three months since ive owned it. Not bad for a certified shade tree tech. I attached pics might help you guy out there having the same issues
 

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2001 Cadillac Deville
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39 Posts
your pictures helped out alot I drove home with codes and after I was done no Codes YES!!! thanks for the pics. I had a tear about a QTR of the way around the Plenum
 

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2001 DTS, 2005 Mustang GT, 2010 MINI S
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1,121 Posts
When mine did it, at first I thought I had some bad gas. Problem started just after leaving a gas station.

Anyway, spraying some carb cleaner around I could hear the leak at the plenum.

Ripped plenum, exactly like yours.

Mine was like $20 at the dealer. The intake gaskets can be reused if not damaged.


Logan Diagnostic LLC
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'98 STS (RIP @ 206,xxx miles)
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4,854 Posts
How do these things develop rips like that?
It sure would be nice to hear from you-know-who on this issue. I don't think we had any reports of similar problems prior to the 2000 model year engine changes.

Material? Vendor? Design? Beats me.
 

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2018 CTS 3.6L AWD Premium Luxury, Previous: 2009 STS 3.6L AWD, 2003 DTS 4.6L
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379 Posts
My guess would be heat. Has me wondering if maybe I should do a little preventative maintenance and change it before it goes bad.........
 

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White Diamond '03 DHS (with DTS floor shift)
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86,987 Posts
Jim,
Pre 2000's did not have the plenums. I think the TB was bolted directly to the manifold, which then brings up the question, why the change?
 

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White Diamond '03 DHS (with DTS floor shift)
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86,987 Posts
Yeah, would be nice to hear from him. I tried to email him recently, but his email address was undeliverable and I don't have his personal address. Even if he was to come back, it would be under a different name and he would never divulge his identity again.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,121 Posts
There should be absolutely no movement between the TB flange and the intake manifold: they're both bolted to the same block, so that sort of rules out excessive flexing.

All the "plenum" problems with cracking appear to occur in the bottom 30 - 45 degrees of the bellows edge. Might this have something to do with a combination of fuel vapor (where from?), oil (PCV) vapor, and the fact that the bottom of the plenum bellows is a natural sump for holding liquid nasties? The GM fix might be as simple as a change to the ingredients used to mold the plenum in the first place, and a real hard look at the molding wall thickness in the break area.

Too bad you can't just clamp a piece of silicone intake hose in there........straight wall, impervious to fuel damage.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,987 Posts
Too bad you can't just clamp a piece of silicone intake hose in there........straight wall, impervious to fuel damage.
I see no reason why you couldn't.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,121 Posts
I think the plenum has a clamping plate on the TB end, not a simple spigot with hose clamp setup.

HOWEVER, an enterprising tuner could have a spigot welded to the (removed and cleaned....) plate, and make the necessary TB gasket......
 

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2002 Cadillac DTS Deville on Vogues and DTS Blades
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605 Posts
maybe i shouldnt ask but who is this mystery member you guys mention?
The General himself or what?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,121 Posts
Almost........I believe the person was heavily involved in the design, testing, and validation of Northstars and running changes. That's 55th party hearsay.........
 

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White Diamond '03 DHS (with DTS floor shift)
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86,987 Posts
I won't mention his screen name as he asked that we let it die a swift and silent death when he left (not that I think it matters anymore), but he is a GM powertrain engineer. He was a great asset and taught us a lot.
 
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