05 STS P0174 and P0171

It's your engine, transmission, driveline
kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

05 STS P0174 and P0171

Post by kevm14 » Sun Dec 02, 2018 8:40 pm

Decided to take a look at the lean codes this afternoon.

I checked a few things and tightened the clamps on the intake plenum duct.

I did find something. The elbow at the rear of the intake that is part of the PCV system was completely falling apart though the rest looked fine. It was very difficult to access and in a surprising location. Rather than a nipple at the back of the intake as I expected, it seemed like a hard plastic pipe ran out the very center of the intake, which was actually hollow. Hard to describe. That plastic tube in the center of the rear is what I am talking about.
ado-19330172_gb_xl.jpg
Getting the spring clamp off was quite a challenge. Ended up using one of my fancy spring clamp pliers but it still was difficult, as there wasn't that much room to work behind the intake.

Here it is in a mirror.
DSCF3671.JPG
Best I could figure in a pinch was 3/8" fuel hose.

Anyway I tried Tractor Supply but the 3/8" fuel hose they had was rated to 175F and specifically said not for under-hood use. I find the engine bay of these cars particularly warm so that is clearly not a good idea. I ended up at Ace which had some 3/8" marine fuel hose, which I hope is suitable. Held it on with some worm drive clamps. Maybe I should get the right elbow.

Anyway I was hopeful that this was my unmetered air leak.
DSCF3669.JPG
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Here's the big ugly fuel hose.
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What did the road test reveal? Well I used my generic tool which happily displays the datastream pretty quickly using the CAN protocol. That's something.

I put up short and long term trims. The verdict is....I think I have a vacuum leak. Under any kind of load the trims even right out and look great. But under lighter load and overrun, they get ridiculous, though the values are also odd, like +18 on the LTFT but also -12 on the STFT. The short term never seems to be able to really correct the long term in some of these circumstances. But the point is, that seems to rule out anything in front of the throttle body. It's something subjected to intake vacuum, I would assume. That helps narrow it down.

I'll drive it some more. Wonder if I need to do the intake and gaskets...I would probably order a plenum duct just because it would make sense to change. But I'm not ordering parts yet.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Sun Dec 02, 2018 8:43 pm

Looks like I can get both PCV hoses with elbows for $10 and $7, respectively, from RockAuto. One is called a tube for "dirty air" and one for "clean air."

I don't think this car has a PCV valve. Also the PCV tubes were not dripping with oil, nor did they smell, at all, like oil.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Wed Dec 05, 2018 9:24 am

A more recent thread.

https://www.cadillacforums.com/forums/c ... p0174.html

Conclusion: that intake plenum duct is apparently common. Maybe I should order one after all. Wish I had a smoke machine though.

bill25
Posts: 2556
Joined: Thu Oct 31, 2013 2:20 pm

Re: 05 STS P0174 and P0171

Post by bill25 » Wed Dec 05, 2018 8:17 pm

Wish I had a smoke machine though.
Yeah then you could make movies like they did in the 80's.

Bonus - Live Band show capabilities too. Also from the 80's.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Thu Dec 06, 2018 10:04 am

Quick Amazon research yielded this as a good choice:
https://www.amazon.com/STINGER-Smoke-Ma ... automotive

Maybe Adam would go in half on it...$75/ea is pretty modest.

These are used to find/diagnose leaks in any automotive system such as:
- Any vacuum line type stuff
- Evap system
- Intake manifold
- Anything that you can seal at either end and want to determine leaks. For example you could shove smoke into your gas tank and determine if the fuel pump top gasket was leaking. Or maybe you'd shove in an evap return line. Either way.
- Probably not A/C

Looks like it uses shop air regulated down to 1 psi.

Amazon also suggests:
https://www.amazon.com/OTC-Tools-CEA-02 ... VVN6PHEBDB

OTC plugs

And
https://www.amazon.com/Vi-Jon-Inc-S0883 ... 6YT0XE0YNM

A 3 pack of mineral oil for making smoke

Total $194.40. Very tempting.

Also I find this quite surprising:
- Engineered by Aircraft Mechanics and priced far below competing machines, the Stinger Pro 2 produces large quantities of smoke and is equipped with a flow control valve and 1-PSI pressure regulator - a safe pressure for testing any automotive system

- Ships SAME/NEXT Day Via USPS Priority Mail - Each Stinger machine is hand-made by skilled craftsmen in the USA - Buy with Confidence
Well that's something. Not made in China.

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Thu Dec 06, 2018 2:12 pm

Better deal on mineral oil.

https://www.amazon.com/dp/B00VNI1JI0/re ... TN1KG6QJPX

Food grade!

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Fri Dec 14, 2018 6:02 pm

Alright so I have the smoke machine and some mineral oil. Haven't looked for the leak yet. MIL hasn't come back at least.

But I just noticed this thread from today on the Caddy forum.

https://www.cadillacforums.com/forums/c ... speed.html
What would cause a low(ish) idle speed while in gear? I know it should be between 600-800, while in gear it's at about 560-600, doesn't go over 600. Fuel trims are higher than normal at idle, noticing a slight vibration. My first guess would be a vacuum leak but I've checked for leaks before and found nothing.
I have more or less the same symptoms.

First reply:
Did you use a smoke machine for leak detection? I tested with water and with flammable brake fluid and found nothing. Made a smoke generator and found the leak. It was the plenum between TB and intake. I am a smoke machine believer.
That's the plenum duct that I was referring to. Probably my issue...

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Sun Dec 16, 2018 6:27 pm

Finally assembled the smoke machine and did my smoke test.

First a few comments on the machine. It is not quite as hassle free as the $800 machines where you dump in some mineral oil, turn them on, and go. Well, technically this is similar, but it uses a wick and wick heater which is powered by 12V using alligator clips. But for filling, you have to fill to a certain level, not let it go up to the heater (which is only an inch up or so) and not let it get too low so the wick doesn't burn. That ends up giving you 10+ minutes of smoke time before shutting off and checking the level. I never did this as I had enough time. It is also powered by air using an LP gas regulator. There is a valve to regulate the amount of air and thus smoke. Pretty simple. It makes a TON of smoke so I turned it way down. What the internet says is true - the vaporized mineral oil is incredibly acrid and awful smelling.

Since I was ready to smoke the intake, I used one of the included step adapters and shoved that into my brake booster hose. Then I turned the smoke on. I must have let it smoke for 5-8 minutes. Smoke eventually began coming out of the intake air box, having made it all the way through the intake, past the almost closed TB and through the air intake tube. I did NOT see any leaks at all around the intake, or that plenum duct, or any of the PCV stuff.

Another downside of the mineral oil stuff (not sure if the pro tools use something different entirely - they may), is it coats everything. I doubt it is harmful but I wasn't that excited about coating the MAF sensor, so I sprayed the element when I was done. I also had to wipe out the TB, air intake tube and the outlet of the MAF body.

But yeah - I could find no leaks.

I did play with the Tech 2 for quite a while in the garage with the car idling (I was also trying to find my coolant leak, also unsuccessful). I ended up resetting the fuel trims. Later on I went for a test drive and at idle bank 2 was 10% on the long term and bank 1 was 3%. Not exactly a problem, or a massive vacuum leak. So....maybe that PCV elbow WAS the issue and I just needed to reset the fuel trims?

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Sun Dec 16, 2018 7:08 pm

If I get the code back, I may try blocking off the TB with one of those OTC caps I bought from the kit. I think I would have seen something anyway though...

kevm14
Posts: 13936
Joined: Wed Oct 23, 2013 10:28 pm

Re: 05 STS P0174 and P0171

Post by kevm14 » Sun Dec 23, 2018 7:27 pm

Trims at idle were pretty decent. Was like 7% and 3% for LTFT or something. Nothing bad at all, at idle.

Beginning to think the PCV hose actually fixed it.

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