: P0171 and P0174 codes: Intake leak?



turbojimmy
07-27-07, 02:44 PM
How common is it for the intake manifold to leak on a Northstar? I made a trip out to Long Island today (100+ miles each way) and while sitting in stop-n-go traffic on the GWB I noticed the car was idling high. When things got moving again the car felt a bit sluggish. On the way home the SES light came on - a P0171 and P0174 were set. The idle quality deteriorated as I made the 100-mile trip and it was missing pretty bad by the time I got home. It was also running warmer than usual (though not 'hot').

I pulled the cover off the top of the engine and could hear hissing as it idled. I used a stethescope to isolate it to the back left (right front as you face the car) of the intake manifold.

Is there anyway to verify that this is the leak without setting the car on fire (i.e., by spraying Gumout around it)? Do these manifolds have a history of cracking or leaky gaskets? The stealer replaced my starter about 2.5 years ago which would have required removing the intake.

Thanks,
Jim

turbojimmy
07-27-07, 03:49 PM
I sprayed gumout around where I thought the leak was and it didn't do anything. So I'm wondering if the hissing is 'normal'? Any ideas where to start diagnosing a lean code?

Thanks,
Jim

JimD
07-27-07, 03:54 PM
....Is there anyway to verify that this is the leak without setting the car on fire (i.e., by spraying Gumout around it)?You could use a Windex spay bottle filled with water.

Do these manifolds have a history of cracking or leaky gaskets?No cracked manifolds that I have seen reported. But there is a rubber seal in there that several folks have had to replace. Lots of pieces have to be removed to get to it too.

There is a thread in one of the model specific forums about this seal just in the past 30 days.

JimD
07-27-07, 04:29 PM
Read through this one
http://www.cadillacforums.com/forums/cadillac-deville-1985-2005-including-1985/112014-p0174-code-driving-me-crazy.html

ewill3rd
07-27-07, 08:04 PM
Yep, plenum is probably leaking.
Look at that thread. A couple of other recent ones too.
I got the parts (at employee pricing) for my mom's car for less than 50 bucks shipped.
Not sure what list price is.

turbojimmy
07-27-07, 08:11 PM
Yep, plenum is probably leaking.
Look at that thread. A couple of other recent ones too.
I got the parts (at employee pricing) for my mom's car for less than 50 bucks shipped.
Not sure what list price is.

Yeah, that's where the noise is coming from - that rubber thing between the TB and the plastic intake manifold. What are all those turquoise looking gaskets in the pics? Do you have P/Ns for the parts?

Thanks,
Jim

ewill3rd
07-27-07, 08:37 PM
Try to PM Luke at "Lindsay Cadillac Parts".
He has part numbers and pricing information.
I know he shipped out a set recently to another forum member for a good price.

I bought a set for my Mom's Aurora and sent it to my buddy who lives close to them so he can fix it for me. (I get better prices than he does)

Give him the last 8 of the VIN to be sure he gets you the right prices.
Not sure if he is working this Saturday or not.

The blue gaskets are intake seals. You need 8. They should not be reused, when you take it apart you'll see why.

turbojimmy
07-28-07, 05:46 AM
Try to PM Luke at "Lindsay Cadillac Parts".
He has part numbers and pricing information.
I know he shipped out a set recently to another forum member for a good price.

I bought a set for my Mom's Aurora and sent it to my buddy who lives close to them so he can fix it for me. (I get better prices than he does)

Give him the last 8 of the VIN to be sure he gets you the right prices.
Not sure if he is working this Saturday or not.

The blue gaskets are intake seals. You need 8. They should not be reused, when you take it apart you'll see why.

Ok I'll shoot him a PM - thanks.

I re-read your post on the other thread and I am also getting that suction noise when I spray the Gumout around the intake. Thing is I got the suction noise toward the front of the engine, not the plenum. I'm going to pull it off and see what's up. Looks like an easy job. Best case I'll need those intake gaskets.

Of course I have to do the work outside. The irony is that this happened as I was delivering the transmission out of my Buick to a guy in NY. The Buick is consuming one bay of the garage; kids toys in the other. Worse is that now I have no transportation. Time to dust off the bicycle.....

Jim

JimD
07-28-07, 06:05 AM
....Thing is I got the suction noise toward the front of the engine, not the plenum.

Before you pull the intake, double check the pressure relief valve at the front end of the manifold. It should be visible directly inboard of the power steering pump.

turbojimmy
07-28-07, 06:53 AM
Before you pull the intake, double check the pressure relief valve at the front end of the manifold. It should be visible directly inboard of the power steering pump.

Too late! But I will check that. Here's what I've got:
http://www.turbojimmy.com/DTS_plenum-1.jpg
http://www.turbojimmy.com/DTS_plenum-2.jpg

Thanks to both of you!

Jim

turbojimmy
08-02-07, 07:17 AM
Well it's fixed now. I drove the car to work today and the idle is back where it should be and there are no codes. Even though that plenum was ripped (looks like it was sliced, actually) I'm not sure that was actually the problem. What I thought was a hissing noise is still there - it might be the power steering pump. There was definitely a vacuumm leak which was causing the lean codes, but I think it was the PCV fitting that connects underneath and in the middle of the intake manifold.

When I removed the intake that pipe simply fell off. If installed correctly it would never fall off - it's a tight fit and the pipe fits in the guide on the intake. Mine wasn't like that. I suspect that when the stealer changed my starter motor they forgot to put that pipe on before they put the manifold back on. If this happens, the only way to install it properly is to remove the intake manifold again. Or, you can try to jam it in there and hope for the best.

The only advice I would have for people doing this themselves is to watch out for the pressure valve at the front of the intake. When you install the intake, you tilt it so that the intake goes down and into the plenum at the back of the engine and then you push the front of the intake down into place. It's a VERY tight fit (power steering pump is in the way) and that rubber plug over the pressure relief port can come off. The other thing is that you need to make sure the plenum is installed securely with the throttle body bolts before you attempt to install the intake. This compresses that plenum so that you get more clearance between the intake and the power steering pump. When you do it you'll see what I mean.

I'm glad to have the car back. I've been driving my dad's SS Camaro, which is fun, but I have to say I missed the ride and creature comforts of the DTS.

Jim

JimD
08-02-07, 07:24 AM
Excellent feedback. Thanks for closing the loop.

ewill3rd
08-02-07, 06:33 PM
My mom's car is supposed to get fixed tomorrow.
I sent the parts to my buddy down that way and he's going to put them on for them.

Glad to hear some of these are getting fixed.

turbojimmy
08-02-07, 08:42 PM
My mom's car is supposed to get fixed tomorrow.
I sent the parts to my buddy down that way and he's going to put them on for them.

Glad to hear some of these are getting fixed.

I'm just curious as to what causes it in the first place. There's no movement between the intake and the TB that would cause that plenum to flex. Mine looked like it was sliced with a knife. Very odd. At least it was inexpensive to fix. The pricing seems wacky though. That rubber plenum, complete with the clamp and metal bracket was $16. Those silly little intake gaskets were $3.xx each and I needed 8 of them. And it's very clever of GM to sell them in packs of 5. When was the last time GM manufactured a 5 or 10 cylinder engine? Answer: never. You have to order 2 packs of 5 (10 of them) to do a V8, which leaves 2 to hang on the peg board in the garage for eternity. Bastages.

Jim

ewill3rd
08-03-07, 08:18 PM
Mom's car is all better now :D

Jimmy, I am not sure what causes it, the failure does look similar on all the ones I have replaced.
I don't know if it is thermal cycling coupled with the stress on the piece or what. I have always thought it looked kind of funny.
It might be affected by some light backfiring or have to do with the way oil and carbon affect the inside of the intake due to the shape of the chamber and airflow... I don't really know.

I can't believe your dealer won't sell you just 8 seals. I do know some places that don't move a part a lot will be sticklers about selling you part of a kit but I think since we move a lot of those seals we just sell them as we need to instead of forcing you to buy 10. Luke could probably clear that up.
I get 8 billed out from parts all the time for customer cars that are in the shop.
(when I do them I mean)

Just think, after you replace the plenum 4 times, the 5th time you won't need any intake seals! :D
You just have to hang on to the extras for about 20 years or so to go through that many plenums.
(just kidding)
When I first started seeing this problem it blew my mind that we had 5 in stock, but it takes 8 to do the job. I had to wait a day usually to get the other 3 to finish the job.

turbojimmy
08-04-07, 12:36 PM
Mom's car is all better now :D

Jimmy, I am not sure what causes it, the failure does look similar on all the ones I have replaced.
I don't know if it is thermal cycling coupled with the stress on the piece or what. I have always thought it looked kind of funny.
It might be affected by some light backfiring or have to do with the way oil and carbon affect the inside of the intake due to the shape of the chamber and airflow... I don't really know.

I can't believe your dealer won't sell you just 8 seals. I do know some places that don't move a part a lot will be sticklers about selling you part of a kit but I think since we move a lot of those seals we just sell them as we need to instead of forcing you to buy 10. Luke could probably clear that up.
I get 8 billed out from parts all the time for customer cars that are in the shop.
(when I do them I mean)

Just think, after you replace the plenum 4 times, the 5th time you won't need any intake seals! :D
You just have to hang on to the extras for about 20 years or so to go through that many plenums.
(just kidding)
When I first started seeing this problem it blew my mind that we had 5 in stock, but it takes 8 to do the job. I had to wait a day usually to get the other 3 to finish the job.

Actually they only charged me for 3. They didn't have any in stock (Buick dealer) but found one local dealer had 3 and another had 5. I didn't realize until I got home that they didn't charge me for the bag of 5, just the bag of 3. I'll have to square up with them next time I'm in there. They've been pretty good to me so I feel like I should point out their mistake.

Jim