terrible gas mileage

smithy · Post by **smithy** » 28 Jun 2005, 08:27

In this age of rising gas prices, my terrible gas mileage has me vexed. I'm looking for a list of items that I can maintain that will keep me in the upper 20's range of the precious MPG. Right now I'm right around 10-15 city.

So far, I have this short list of items that can affect mileage:

1- O2 sensor
2- Vacuum leak
3- dirty air filter
4- dirty fuel filter
5- poor tire tread/alignment
6- dirty transmission fluid
7- Mass air flow sensor

If I am way off base here, please let me know. Also, I know there are more things that can be a cause. I just don't know what they are, except for things like a strong headwind on the highway. I'm about to go ona trip and would like to keep my fillups to a minimum so I'm looking to do some of this maintenance before I go. any help will be greatly appreciated. Thank you.

Jot · Post by **Jot** » 28 Jun 2005, 08:46

How many miles on the vehicle? whatyear ? If no codes put #7 at the top of the list

smithy · Post by **smithy** » 28 Jun 2005, 09:34

It is a '98 S70 GLT with 95,000 miles. I do have a code (P0410-secondary air injection malfunction) but I don't know if it is indicative of fuel efficiency. I don't believe it to be a MAF because it checked out just fine recently. Thanks for your response to this post as well as my other one about the P0410 code.

Post by **matthew1** » 28 Jun 2005, 10:36

Try cleaning and reseating the MAS (careful).

Did your economy drift down to 10-15 -- an O2 sensor telltale sign -- or fall quickly?

smithy · Post by **smithy** » 28 Jun 2005, 11:44

I never paid attention to my mileage until I got a code for my O2 sensor and started paying attention to it. I've since replaced the sensor and did not get the improvement in my efficiency that I had expected. That is why I'm trying so hard now to locate other causes. As far as my MAS is concerned, I'm a little hesitant to mess with it since I actually broke the one from my '94 850 and had a hec of a time finding a replacement. Once I do all of my filters and such with no improvement, I will look into the MAS.

As far as the SAS valve/Air pump code, do you think this can have adverse effects on fuel economy?

Mr. Norm · Post by **Mr. Norm** » 28 Jun 2005, 12:03

Best guess(es)

1. Vaccum leak
2. O2 sensors, I think these are supposed to be changed every 80k or sumthin.

Either of these will kill yer mileage.

adrian22 · Post by **adrian22** » 29 Jun 2005, 09:56

I had same problem, and turn out to be the incorect or falty(volvo part) sensor .I hat to change 3 sensors all new and recomended by on lines supliers in order to get a decent one .I have now 19 in city and 30 outside.Have your o2 sensor tested before you mes up you others things

rokkein · Post by **rokkein** » 21 Jun 2007, 13:39

I'm experiencing similarly bad mileage on the used 850 Turbo I recently purchased. There are no engine service lights on. Would all of the above issues necessarily set off a service light, or might one have failed without notice?

I have a new air filter, new oil, 1 yr old battery. I'm using regular gas (not premium). Don't know about the spark plugs or any of the other sensors.

Trilarry · Post by **Trilarry** » 21 Jun 2007, 20:04

Check your O2 but if it hasn't been tuned up do so.
Change your plugs, cap and wires if you can afford it. All in all tune it up and go from there. Fuel filter should be included in this also. You should see some improvements, than we can troubleshoot further.
Tri

waynej · Post by **waynej** » 21 Jun 2007, 20:34

After replacing the plugs, plug wires,cap and rotor, then get it up to highway speeds for at least 30 minutes to burn the carbon off the o2 sensor. You may also have very dirty fuel injectors. Dirty injectors don't properly atomize the fuel and it doesn't burn completely. Chevron puts injector cleaner in all their grades of gasoline. Most other companies put little or non in the lower octane fuels. You can buy a good cleaner from Chevron or Red Line. The instructions on the cleaner say to put a bottle in a full tank. I put a bottle in a 1/4 or 1/8th tank. Then take it out on the interstate when it's not to busy, accelerate to 75 then slow to 40 and accelerate to 75 again. Do this about 5 or 6 times then fill the gas tank. If you leave the high concentration of cleaner in the system for more than a few hours the rubber seals may turn to mush.