1996 850 GLT P0172/Running Rich

TBrown00 · Post by **TBrown00** » 21 Apr 2015, 16:47

I have 174k mi on my 854 and recently had an on/off P0172 code and found a cracked vacuum hose from the IAC to the tree. When checking the freeze frame and live data, the LT and ST fuel trims were normal. Long term was between -0.8 and 1.8%. I replaced the hose (unfortunately URO was the only thing my local parts guy had, but it'll do for now) and reset the code and it hasn't came back yet.

However, the O2 sensor is still reading rich. I've attached photos of the live data readout from my Autel of the O2 voltage and STFT at idle. The readings now are the same as before replacing the hose.

I redid the PCV system and replaced all the smaller vacuum lines from the tree a couple thousand miles ago and the O2 sensors are original. Looking for ideas on what could be causing the persistent rich condition. The O2 sensor used to report normal values. I have 1995 854 that I can swap parts between. The car ran fine when the code was thrown and also runs fine now at idle, under load, etc. I wouldn't have known anything was going on had the code not appeared.

: o2 voltage; IMG_0304.jpg (67.89 KiB) Viewed 1547 times

: STFT 1 of 3; IMG_0305.jpg (63.53 KiB) Viewed 1547 times

: STFT 2 of 3; IMG_0306.jpg (65.55 KiB) Viewed 1547 times

: STFT 3 of 3; IMG_0307.jpg (60.01 KiB) Viewed 1547 times

draser · Post by **draser** » 22 Apr 2015, 06:46

Try creating a lean condition and see if o2 responds going down in voltage, just to confirm it's reading correctly. If that passes get trim readings at 1500 and 3000 rpm. If trims start towards zero you have leaky injectors. Look also for loose PCV line going into intake.

Post by **Ozark Lee** » 22 Apr 2015, 16:03

draser wrote:Look also for loose PCV line going into intake.

+1

Ninety nine times out of one hundred that elbow at the end of the intake manifold from the PTC valve is the culprit.

...Lee

TBrown00 · Post by **TBrown00** » 22 Apr 2015, 18:09

draser wrote:Try creating a lean condition and see if o2 responds going down in voltage, just to confirm it's reading correctly. If that passes get trim readings at 1500 and 3000 rpm. If trims start towards zero you have leaky injectors. Look also for loose PCV line going into intake.

Pulled a vacuum line from the tree and o2 voltage shot down to .370 instantly.

Then reconnected the line and watched the STFT at idle and it stayed pretty stable except at one point it shot to -16% and the idle speed changed a little (see photos 2 and 3 below). Then tested at 1500 and 3000rpms once it stabilized again.

Ozark Lee wrote:
draser wrote:Look also for loose PCV line going into intake.
+1

Ninety nine times out of one hundred that elbow at the end of the intake manifold from the PTC valve is the culprit.

No PTC for me since it's a 96 GLT. The vacuum line for the PCV on my car goes from the flame trap to the tree.

: o2 voltage with vacuum line pulled from tree; IMG_0314.jpg (64.15 KiB) Viewed 1547 times

: STFT at idle; IMG_0315.jpg (72.41 KiB) Viewed 1547 times

: STFT change at idle; IMG_0318.jpg (71.59 KiB) Viewed 1547 times

: STFT at 1500rpm; IMG_0319.jpg (78.15 KiB) Viewed 1547 times

: STFT at 3000rpm; IMG_0320.jpg (61.31 KiB) Viewed 1547 times

Post by **erikv11** » 22 Apr 2015, 20:47

TBrown00 wrote: ... No PTC for me since it's a 96 GLT. The vacuum line for the PCV on my car goes from the flame trap to the tree. ...

The line is still there on a 96 GLT, it came from the factory with a line from the flame trap to the intake manifold, not to the tree. So is that pesky connection Lee is talking about capped off right at the intake manifold on your car?

TBrown00 · Post by **TBrown00** » 22 Apr 2015, 22:10

erikv11 wrote:
TBrown00 wrote: ... No PTC for me since it's a 96 GLT. The vacuum line for the PCV on my car goes from the flame trap to the tree. ...
The line is still there on a 96 GLT, it came from the factory with a line from the flame trap to the intake manifold, not to the tree. So is that pesky connection Lee is talking about capped off right at the intake manifold on your car?

According to the vacuum diagram under the hood it goes to the tree. That's also how the factory yellow plastic/black rubber elbow line was hooked up when I replaced it. I don't remember seeing that port on the passenger side of the intake manifold when I did the PCV. You guys know way more about these than me though so I'll double check the side of the intake manifold when I get home.

TBrown00 · Post by **TBrown00** » 23 Apr 2015, 00:40

Just double checked and there's no port on the passenger side of my intake manifold. Just to confirm, we're talking about this port right?

: intake manifold.jpg (54.97 KiB) Viewed 1537 times

Mine just has the circle, but no hole or anything. It's a flush surface with the rest of the manifold.

mika · Post by **mika** » 23 Apr 2015, 07:50

yes, that is it. goes from flame trap by throttle , under the intake, over to what you posted (pass side). If this line is severed or not connected, you usually hear a distinct hissing

Post by **mecheng** » 23 Apr 2015, 07:52

That is indeed the port

Post by **erikv11** » 23 Apr 2015, 08:27

TBrown00 wrote: ...Mine just has the circle, but no hole or anything. It's a flush surface with the rest of the manifold.

Lucky you! Maybe it's a CA emissions variant, I don't know ...

Could you post up or PM me a pic of your emissions sticker? I would like to add it to another thread that talks about vacuum lines on NA cars.