1996 850 GLT P0172/Running Rich

[draser]

From your readings it looks like negative trim is proportionate to rpm, if I read correctly. Leaning towards fuel pressure/regulator. I'd measure fuel pressure and check regulator operation. If you have a return line from reg I'd squeeze it to see idle chenges. If your scanner reads MAF I'd post idle/1.5k/3k rpm readings perhaps someone with similar engine can volunteer theirs for compare. Good news is o2 sensor seems to work. One question is I don't see your long trim being 20-25% negative to trigger the code, maybe I missed it?

[Ozark Lee]

My '94 manual N/A car doesn't have that port either but that is a Jetronic LH 3.2 system. I'm trying to remember where the PCV lines go on that car and I'm coming up blank.

...Lee

[TBrown00]

...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.

My brother has a 95 850 GLT and he has the same vacuum routing. My car was initially purchased out of state and brought to CA. I believe his has always been a CA car though.
PM sent. That thread was very helpful when I redid my vacuum lines recently. Glad to give back to it!
If anyone in this thread is interested I'm happy to post them here as well.

From your readings it looks like negative trim is proportionate to rpm, if I read correctly. Leaning towards fuel pressure/regulator. I'd measure fuel pressure and check regulator operation. If you have a return line from reg I'd squeeze it to see idle chenges. If your scanner reads MAF I'd post idle/1.5k/3k rpm readings perhaps someone with similar engine can volunteer theirs for compare. Good news is o2 sensor seems to work. One question is I don't see your long trim being 20-25% negative to trigger the code, maybe I missed it?

Ya I can't figure out what that small blip in the throttle and the drastic change in STFT have to do with each other. The car continued to idle just fine and I wouldn't have known anything was different had I not been watching the scanner. It had been idling a few minutes at that point. I don't have a fuel pressure gauge handy, but can pick one up to do some testing. I'll play with the return line tomorrow.

Here are the MAF readings:
Idle: .01 lb/s
1.5k rpm: .02 lb/s
3k: .04 lb/s

When I checked the freeze frame data before clearing the code, it said the STFT was 1.8% and the LTFT was -0.8% when the code was set. I checked/cleared the code twice and had similar numbers the first time as well. I was surprised it threw a rich code with the fuel trims at those numbers. I was expecting to see the LTFT around the same numbers you mentioned above. I kept my eye on the LTFT and saw it change to -1.8% and 0.8% over the period of a few days. Nothing more than that ever - even with the o2 reading rich.

My '94 manual N/A car doesn't have that port either but that is a Jetronic LH 3.2 system. I'm trying to remember where the PCV lines go on that car and I'm coming up blank.

...Lee

Here's my vacuum diagram and I've circled that line in red.

Vacuum diagram

[draser]

MAF readings look pretty liniar, so unless the base one is off, someone may jump in with their number, I'd say it's perfect. I'd also swap the o2 sensor from other car to confirm readings.

[erikv11]

TBrown00's car seems to be Motronic 4.3 with EGR and you don't see a lot of those, most 96's that I have seen are 4.4 with an air pump (http://new.volvocars.com/ownersdocs/199 ... n1996.html). Good to know, I added this configuration to https://www.matthewsvolvosite.com/forums ... =1&t=65002 on page 2.

[TBrown00]

MAF readings look pretty liniar, so unless the base one is off, someone may jump in with their number, I'd say it's perfect. I'd also swap the o2 sensor from other car to confirm readings.

Thanks. I won't be able to do that until tomorrow, but I'll swap them and report back with the results.

[TBrown00]

Wasn't able to swap the o2s this weekend but did make some progress. The o2 sensor voltage is now reading between .350 and .950.

Using a MAPP torch I found a couple leaks pulling unmetered air in. Found one around the throttle body and another on the accordion tube going from the airbox to the TB. I found a few cracks in the airbox tube since it's gotten old and dry and lost its flexibility. Replaced the TB gasket and swapped over a good airbox tube from the 95 850 and couldn't locate any other leaks. I tried both ends of all the vacuum lines as well as all parts of the intake system past the MAF.

Also, I checked the MAF readings on the 95 and they match up with the ones from my 96 I reported earlier in case anyone was curious.

I appreciate all the help/advice from everyone here on this problem.

Also narrowed down a suspension noise to a spring seat and discovered I have CV boots starting to tear. The joys of owning a 19 year old car with rubber parts that are past their lifetime.

[John850GLT]

I have same car and code. If you have resolved the problem is like to hear. If not, 172 indicates unmetered air, and that could be a hard-to-see but common tear in the flexible air hose from filter to throttle intake. I put a non-OEN replacement on a while back; stretching it revealed cracks recently. Car runs, as yours, does, without issue