1998 V70 GLT - Poor Gas Mileage After Tune Up

Seaway · Post by **Seaway** » 23 Jul 2014, 08:40

Bought the car with 214,000 miles. It ran a bit rough and misfired every once in a while and was getting about 15 mpg in 90% city driving with the AC on. I was hoping for better fuel economy, so I proceeded to do the following:

New Volvo plugs
New Bougicord plug wires
New Bosch Distributor Cap
New Bosch rotor
New Bosch MAF
New Mann Air Filter (removed stock sized K&N filter that was in the car)
Oil Change (Mann filter - Mobil 1 oil)
Reset ECU (well, unplugged battery and hooked pos and neg cables together for 30 minutes or so)
New AC Delco BCS to replace Volvo TCV
New silicone vacuum lines (still need to replace line to turbo compressor, but it is not broken or leaking as far as I can tell)

After all that has been done I am now getting the same 15 mpg in 90% city driving with the AC on. There has been no increase, and no decrease. The car is running very well with the exception of a little "roughness" as I accelerate in 1st gear (automatic trans). This rough acceleration is present about 90% of the time. After 1st, the car is very smooth through the gears. I am not heavy on the throttle and I am running 93 octane gas from name brand stations.

I guess at this point the only thing I have not done to get the car to Stage 0 is the O2 sensors. I have looked at all the vacuum lines and elbows and don't see anything broken or leaking, I have deleted the SAS pump via the diode method (I have not removed any of the parts, however).

I am hoping to get closer to 20 mpg around town. 18 would make me happy. Is that a realistic goal? Should I just bite the bullet and replace the O2 sensors? I have no idea when they were last done. I have no codes and no CEL.

Post by **rmmagow** » 23 Jul 2014, 09:32

At that mileage and if you don't know its O2 sensor history it would be a good plan to replace them. But even that probably isn't going to get much, 18 maybe though. My V70 AWD (no propshaft) was showing 18 MPG when I bought it and I know the guy I bought it from drove mainly around town with it and hadn't reset the mileage computer for ages. I am now showing 23.5 mpg but run hard and fast for 100 miles a day.

Seaway · Post by **Seaway** » 23 Jul 2014, 09:39

I was thinking what it could probably use was an extended highway run. I did run a bottle of Techron through it when I first got it, but it didn't seem to have any impact. Techron did wonders on an old Benz I had that had been sitting for a while. I am aware my mileage hopes may be out of line with what is possible or likely, I guess I was just anticipating some sort of measurable change after the tune-up I did on the car.

Post by **matthew1** » 23 Jul 2014, 09:39

Yep, I'd do O2 sensors next. Front first. You should see better than 15mpg. You're on the right track, right thinking, Seaway.

Seaway · Post by **Seaway** » 23 Jul 2014, 09:45

matthew1 wrote:Yep, I'd do O2 sensors next. Front first. You should see better than 15mpg. You're on the right track, right thinking, Seaway.

Time to place another order then... I am likely going to try to hang on to this car for a while. I love the way it drives and it handles well for a heavy wagon. Needs struts and maybe a a tweak of the wastegate actuator and I think it will be a fun car for a few years.

Post by **rspi** » 23 Jul 2014, 10:01

Do a compression test, a weak motor may use more gas.

Post by **matthew1** » 23 Jul 2014, 10:14

rspi wrote:Do a compression test, a weak motor may use more gas.

^ Yes, this too. Borrow or buy — for just a few tens of dollars — a compression test tool. https://www.amazon.com/gp/product/B001Z0 ... wsvolvo-20

It sounds like you don't need anyone to tell you to work from the simple to the complex, aka, the cheap to the expensive. But there it is.

Seaway · Post by **Seaway** » 23 Jul 2014, 10:31

What compression numbers am I hoping to have? And what differential would be unacceptable across all 5 cylinders? 5%? 10%? I have never done a compression test on any vehicle/engine. Probably time to learn...