1998 v70xc MPG difference w/bad cat &/or 02 sensor

Post by **shiloh51933** » 31 May 2015, 09:35

6 months ago I had to get rid of my 96 850 and replaced w/98 v70xc that had some issue but ran fairly well w/good interior & exterior. Struts are shot, front was shot but I repaired/replaced & aligned, has oil leaks but I've repaired all but one oil line and it smoked upon heavy acceleration. I cleared up smoking issue(rear cam seal into dizzy cap/rotor), I had to replace MAF, turbo wastegate solenoid, plugs & wires, SAS pump, battery replaced, filters, recharge refrigerant for AC and some vacuum lines were bad. In short that is what I done so far and now I'm having an MPG issue, I mean it's bad. I'm getting about 12 mpg if I'm easy on throttle and I'm thinking cat is shot along with pre cat o2. I'm thinking all the smoking/heat killed cat and fouled up o2. I've just never seen such poor MPG's with a bad cat, I'm curios to know other Volvo enthusiast experiences with similar issues.

Sommerfeldt · Post by **Sommerfeldt** » 31 May 2015, 12:09

12 mpg is poor, that's for sure.
First stop should probably be reading your DTCs, or have you done that already?

- S

Post by **misha** » 31 May 2015, 15:55

Which codes are stored in ecu?
Could be numerous things.

Post by **FLXC90** » 31 May 2015, 16:02

With all the work you have done, depending on the order in which you did it, have you tried disconnecting the battery and resetting, then doing a relearn cycle?
as I recall, it's like this: with engine warmed up to operating temperature, disconnect battery, press brakes or touch cables together, reconnect battery, idle for one minute in park, one minute in neutral, select drive, accelerate up through gears at 1/2 to 2/3 throttle until upshift to 4th (D), cruise at light throttle for a couple miles, come to full stop. (but check around- it's been awhile since I did this) After changing MAF, IAC, O2 sensors, anything that affects A/F ratios, this is a completion step.

Post by **shiloh51933** » 31 May 2015, 17:13

Sommerfeldt wrote:12 mpg is poor, that's for sure.
First stop should probably be reading your DTCs, or have you done that already?

- S

I should have listed them yes... P0172 running rich and P0131 o2 sensor low voltage. Anything else I've had I believe has been taken care of as I mentioned in my first post. I can't find any issues with vacuum hoses, she runs like a champ, the exhaust is quiet, turbo is kickin in but freeze frame states she's in open loop w/fault.

Post by **shiloh51933** » 31 May 2015, 17:50

FLXC90 wrote:With all the work you have done, depending on the order in which you did it, have you tried disconnecting the battery and resetting, then doing a relearn cycle?
as I recall, it's like this: with engine warmed up to operating temperature, disconnect battery, press brakes or touch cables together, reconnect battery, idle for one minute in park, one minute in neutral, select drive, accelerate up through gears at 1/2 to 2/3 throttle until upshift to 4th (D), cruise at light throttle for a couple miles, come to full stop. (but check around- it's been awhile since I did this) After changing MAF, IAC, O2 sensors, anything that affects A/F ratios, this is a completion step.

Unfortunately this process has failed to improve my mpg issue. I just can't believe how bad the mpg's are, I know the mpg should be off but I've never seen this low mpg from a bad cat and/or o2 sensor. I do major driving daily, over 100 miles a day and this is killing my pocket!! I posted the 2 DTC codes(P0172/P0131) that are still popping after a few start ups. She's stuck in open loop , so I was thinking of swapping in a new Bosch o2(upstream) when I get paid. Thank you for your input and I'll be looking foward to any more input if you come up with any more ideas, thanks.

Post by **shiloh51933** » 31 May 2015, 17:52

misha wrote:Which codes are stored in ecu?
Could be numerous things.

P0172/P0131

Post by **matthew1** » 31 May 2015, 18:16

Sounds like the "evil elbow" vacuum line.

https://www.matthewsvolvosite.com/forums ... =1&t=56647

https://www.matthewsvolvosite.com/forums ... 33#p322233

draser · Post by **draser** » 31 May 2015, 19:36

Your ECU runs in open loop due to low/no signal from pre cat o2 sensor. You could confirm by looking at signal with code scanner. If wiring is good and connector is clean and tight you need a new sensor. If sensor is narrow band you can measure signal at connector to confirm. If you measure 0.45 volts with engine cold, then 0.1 to 0.8 with engine hot sensor's good probably.

Post by **shiloh51933** » 31 May 2015, 21:07

matthew1 wrote:Sounds like the "evil elbow" vacuum line.

https://www.matthewsvolvosite.com/forums ... =1&t=56647

https://www.matthewsvolvosite.com/forums ... 33#p322233

Sorry to say that elbow line is fairly new and mounted properly. Thanks.