- This topic has 2 replies, 3 voices, and was last updated 9 years, 8 months ago by
.
-
Topic
-
I have a 1996 Volvo 850 GLT with 174k that’s currently running rich, but I’m unable to find the cause. I had a P0172 code pop up, located a cracked vacuum line from the IAC to the tree, replaced it, and the code hasn’t came back yet. However, when looking at the live OBD2 data, it’s reading rich and the same as before I replaced the line.
A little history on the car:
A few thousand miles ago I replaced/cleaned the PCV system and replaced all engine vacuum lines with silicone (except of course the one above which cracked and is now replaced). Everything was fine up until a couple weeks ago.
All of the emissions system components are original except the purge valve and 2 EVAP lines – the car has been problem free its entire life (I have all maintenance history from the previous owner). I’ve owned it for 3 years.
Was originally purchased out of state and brought to CA (I want to say TN or MO area).Current problem:
Vehicle runs fine and you wouldn’t know anything was wrong except for looking at the OBD2 data, which was prompted by the CEL coming on. Even when the light was coming on the car was running completely normal. No starting issues, idle issues, hesitation, or anything.
Here’s the weird part: when the CEL came on (freeze frame data) and current live data the STFT was at 1.8% and the LTFT was at -0.8%. I was expecting to see it around -20-25% when the CEL illuminated. The live data then and now showed the front o2 sensor reading rich though. It was fluctuating between around .45 and .95v. It used to fluctuate within the normal range.
I’ve rechecked all vacuum lines and they are all secure. I’ve attached photos below showing live o2 voltage and STFT w/ RPM data. While idling the other day and watching the data, I was able to catch a quick throttle drop/blip (40rpm) accompanied by a large STFT change (-16%) that was unnoticeable to me sitting in the driver’s seat. Had I not been watching the scanner, I wouldn’t have known anything had happened.
When I pulled a vacuum line, the o2 sensor responded immediately and dropped to .37v.
I’ve ran STFT and MAF tests at idle (840), 1.5k, and 3k rpm. I’ve included photos of the live data graphs below for the STFT tests. MAF results came back as .01 lb/s, .02 lb/s, and .04 lb/s respectively.
Car enters closed loop very quickly after starting up.
Both times the CEL illuminated prior to replacing the cracked IAC hose, the freeze frame data showed the RPMs to be at idle.I have a 1995 850 GLT I can swap parts with.
Any and all advice is appreciated. Thanks!
Attachments in order are:
o2 voltage at idle
o2 voltage with vacuum line from tree pulled
STFT at idle
STFT at idle with change
STFT at 1.5k
STFT at 3k
-
Replies
-
is the cel currently on? any current codes? the fuel trims look acceptable. have you tried cleaning the maf sensor (if it has one)? you could try an injector cleaning. could have one or 2 that are slightly sticky maybe staying open just hair too long. another thing that gets over looked sometimes is the cooling system. very important. it may go into closed loop but if the t-stat isnt reaching the temp its supposed to, or if the coolant temp sensor isnt working properly, the computer might think the car isnt up to temp and will add more fuel to bring the engine up to temp. intake air temp sensor can sometimes do the same thing. you mentioned a short sudden drop out from the tps causing a rich condition at the same moment. its also a possibility. it could also be the o2 sensor itself.
- You must be logged in to reply to this topic.