Getting only 15-16 MPG combined driving...

Post by **jblackburn** » 11 Jun 2013, 22:12

Volvich wrote:Thanks for your posts people. I did change spark plugs (NGK Irridium), put new bosch cap n rotor, fuel filter, took off the throttle body and cleaned it (wasn't that dirty), put a new gasket.

And still... getting only 15-16 mpg. Well, if I do lots of fwy it gets to ~18 never exceeds 20mpg.
Don't know what else could be wrong there. I had the lower control arms replaced w/ genuine volvo parts and alignment done. no check engine light, no codes.

Anyone having the same problem? Any ideas where should I look next?

How does power feel? My old S70's been getting horrible MPG - turns out the CBV on the turbo is bad and it's not really boosting at all.

nedro018 · Post by **nedro018** » 11 Jun 2013, 22:53

go to volvo speed bay 13 docs or to most excellent rspi007 vids on youtube for access to the O2 sensor(s) theres 2 not 1, 1 before the cat converter and one after. $100/ea.

my O2 sensors were replaced 50K ago. they should NOT be bad. bosch brand from FCP. back then, 50K ago.

still, my in-town gas milage was sucking at 19 mpg so i swapped new AFilter and plugs (vovlo), dist cap/rotor were oK so i sanded finely. no help.

then i ordered new front O2 sensor.

went from 19 mpg in town to 23-24 mpg in town. 35 hwy. prob will change rear O2 now. before changing rear, as of now, my combined is 27.5 mpg.

the O2 sensors are impt...they are the last line of defense for the computer to know whats happening. think about it. it is last sensor for the computer....

Post by **abscate** » 12 Jun 2013, 08:21

You can remove the air cleaner box and fresh air pipe to get a clear shot at the front O2 sensor

Volvich · Post by **Volvich** » 16 Jun 2013, 16:40

abscate wrote:Can you take a picture of the old plugs and post? Sounds like you are running rich.

I threw the plugs away. They didn"t look bad at all though.

jblackburn wrote:How does power feel? My old S70's been getting horrible MPG - turns out the CBV on the turbo is bad and it's not really boosting at all.

Was it not switching the lines? I'll check mine and the hoses as soon as I get the chance. I suspect i will need to change the hoses anyways since most of the hoses i haven't changed yet are brittle. The power feels ok at lower rpms (<3,000) but i guess it's supposed to produce more power than it does now above 3,500 rpms. If I floor the throttle, engine revs and sounds mean, I can hear the turbo as well, but I am not sure if engine gets enough air there. Earlier i wrote that it feels like the engine can't "breathe" properly. I'm not a pro, I can't tell but that's what I feel intuitively.

I recently passed the smog check ('98 C70 is an exempt in CA. The guy tailpiped it). I guess if the O2 sensor was bad or if it ran reach it wouldn't pass?

Volvich · Post by **Volvich** » 19 Jul 2013, 16:00

Update: a month ago turbo quit kicking in. The power sucked big time (should say the lack of it).
Turned out the waste gate actuator was the culprit. Had a mechanic fix it. The power feels better than ever, but... still getting that low MPG :/

Post by **abscate** » 19 Jul 2013, 20:12

I've since replaced both sensors and mileage went from 25 to 29mpg at 65 mph

1999 v70 T5 manual trans, high pressure turbo

Volvich · Post by **Volvich** » 23 Jul 2013, 16:23

I wonder if its possible that the sensors are bad although there's no CEL/fault codes?
Did your old sensors cause CEL to come on?
I suspect sensors on mine are "on their way" but not completely dead thus no CEL.

Post by **abscate** » 23 Jul 2013, 18:39

They did not show a code, but clearly they were past End of life. I believe Volvo recommendation is to replace at 100k miles

Post by **E Showell** » 25 Jul 2013, 15:28

Don't wait on replacing sensors. I am convinced that a failing front sensor killed my engine prematurely. I suspect the failure mode was increasing leaning of the mixture (which gave me great gas mileage while it was dying, by the way). A lean mixture caused hot running and lead to a burned exhaust valve. Of course I can't provie it, but it is the only thing that makes sense.

Volvich · Post by **Volvich** » 02 Aug 2013, 14:24

Alright folks,
both O2 sensors were replaced yesterday! I had to remove the turbo inlet tube to get to the connectors. It's too narrow there. Good thing is I had a chance to clean the PTC valve. It wasn't too clogged though.
I was wondering if I should reset the ECU and if there's a special cycle that will let it relearn?

Getting only 15-16 MPG combined driving...

Re: Getting only 15-16 MPG combined driving...