Hey Volvo enthusiasts,

For the past year, my girl's 2000 S70 N/A has been experiencing horrible gas mileage. She loves the car, and we have 4 S70s to show the love. But recently, she's been getting 13 mpg city driving, and it's hurting at the pump here in Canada, especially when 91 gas hit $1.65 (thank god the prices dropped, we started using the bus to be honest).

This city driving used to be more than 21-22 mpg. If anything, highway remains at 35-36 mpg, which is absolutely awesome (or 6.5L/100km average)! (98km/h with tires inflated to 40 psi ftr - old grandpa here).

We've changed spark plugs, MAF, IAC, PCV, ICV, front O2, EVAP valve, AF, ABS & sensors checked, t-stat, new brake pads all round and smooth rolling rotors, synthetic engine and transmission oil ... but still can't find the problem. From nowhere, 21 mpg to 13 mpg ... it's been like this for more than a year, and, I'm stuck. We thought that bad gas (water) might have been the culprit, but after serveral dozen new tanks of good gas, no change.

I'm beginning to think it's a vacuum leak, but for the life of me, have spent hours trying to find it, and nothing ... weird thing though ... it only happens from a complete stop, whether you hit the gas, or tap it lightly.

Let me try to explain what I see:

At a stop, as soon as I release the brake and barely touch the gas, the car registers 50.0 L/100km on the instant fuel economy. As much as I would like to disagree with the computer, the pump is saying the same thing.

If I wait a few seconds after releasing the brake, pissing the people off behind me, and letting the car creep forward, either on it's own or with a slight touch of the gas, (ie: 5 miles an hour), the consumption starts at 50.0 ... then slowly drops to something acceptable. Once the drop stabilizes, then, when I step on the gas as I'm rolling forward, it's normal and gets about 21 mpg city. It's been consistent, from a stop, and whether I creep forward, slowly acceleration or hammer the gas, it's always the same thing.

Now, if I roll through a stop, and notice that the instant fuel economy never has a chance to reset to "- - - -", then mpg is normal after I accelerate. But as soon as the instant fuel economy registers "- - - -", something happens in the engine and tells it to start at full 50.0L/100km once the car starts moving again.

So, what I wanted to know is, what sensor turns on and off when the car is stopped, then rolling. Or if anybody has the same problem and figured out a solution ... I would greatly appreciate it.

As a differential Dx, I have observed all the variables on the OBDII port using torque and android (not that it's anything special, but definitely better than not having anything at all), and if I see something weird, it would be the vacuum and the engine load. Vacuum in neutral and park remain at -21-22, and, in drive drops to -7 to -15 when taking off from a stop, and the engine load registers 30% without any true car load. If I roll thru the stop, vacuum remains at -21 -22. Weird!!! Makes me think there is a vacuum leak in the transmission when the car goes from a stop to drive.

Now, I understand that there must be an unmetered air leak somewhere, and I'm tending to believe it has something to do with the EVAP system at this stage, but if someone has any experience here beyond the aforementioned changes, I sure would appreciate some help.

Thanks in advance,
M

 

Wow, my S70 gets 17 in city and probably around 20 Highway, I feel your pain. Robert' daughter' s70 gets upwards of 21 in city and I am very curious as to how that happens. Sometimes I just think the upkeep of the car over the years can seriously affect the MPG of the car. Have you tried putting premium in? It shouldn't raise the gas milage by very much at all but my car seems to perform better with premium.

 

Have you tried a smoke test to see if you can find a vacuum leak? Here's a thought - check the timing belt to see if the marks line up. Its possible your valve timing can be one notch off and that would hurt gas mileage to the levels you've seen. Its possible somebody did the timing belt and didn't line things up. Does the engine seem to have full power (ie a partially clogged cat?). I take it its not throwing any codes.

 

Thanks for the comments lads,

Well, coincidently, the car died on idle today; as the snow hits the ground, this cold and humid April 23, the car wouldn't start and keep idling. This happened before and it was the MAF in my other S70.

So, I disconnected the MAF and still, the car couldn't keep idle and died moments after ignition. The only way to keep it going, was to press on the gas and hold the rpm's to 1500-2000. And just a quick comment, the car would stall instantly when i pressed on the brakes, even at 1500-2000 rpms.

Now, for quick answers:
always 91 gas (premium), and yes, the car drives better with 91 ... better mpg, more hp, better sound, etc ...
city driving avg 16.9 L/100kms (that's 13.9 mpg) for this last tank,
highway remains at 7.1 L/100kms (33.1 mpg) and many times, averages 6.5 (36 mpg),
no codes,
and yes, full power.
Always maintained at regular intervals ...
car has more than 305,000kms (190,000miles) ...
will check cat and do smoke test (or something similar).

Money is no object when it comes to maintaining the car ... my girl's life and security is more important than colored paper. She loves the car and it has absolutely no rust and still looks mint (great job Volvo).
Honestly, we would like to get it to 500,000 kms (300,000 miles) for bragging rights.

After the car died today, I probed my girl ... now she tells me that the car had a hard time "warming up" (t-stat and ECT???), not like my S70. She also said the transmission was acting up (erratic in low gears) ... and the car "didn't want to move when i hit the gas" occasionally.

After hearing this, I'm thinking ETM ... and I believe the MAF finally died today trying to compensate.
Going to replace them in the next few days.
I'll keep you posted ...

M

 

Have you done a compression test? Any codes set? Do you have a scanner (OBD2) where you can read the fuel trim? Clogged cat?

ETM problems should set a code. If you replace, look at xemodex.

 

Just to share my S80 2001 which is having almost similar problem. In my case, when first move from a stop then the instantaneous consumption will swing to 99.9L/100km and remain unchanged for few second before getting normal at 8-10L/100km. However, I notice the average consumption has increased to around 12L instead of previously 9.5L (mixed city/highway drive)

 

So, as the world turns,

Fixed the stallling issue; a vaccum line from the MAP sensor had ripped - caused the major erratic and stall issues.

Smoke test (friend's cigarette smoke test ) helped find both the MAP problem and the small hairline crack stated below. Compression test showed slightly lower values, which, as described, shows signs of engine wear considering we're at 300k, but nothing really out of the norm.

So, update on the MPG: at least I got it back up to about 18 city mpg ... in and on the NA model air box, there is a second thermostat, and, vacuum line. The air box t-stat was completely shut, allowing only hot air (sometimes reaching 185 degrees farenheit) from the engine to enter the breather box, and, there was a small hair line crack in the vaccum line which only seemd to react under stress. I "modded" the air box by completely removing the intake tube and t-stat, and bottom half of the breather box, turning the air box 90 where the air filter is facing the front just behind the battery. And, removed the vacuum line completely and plug the hole in the intak manifold. LOL ... it's so much throatier now, with deep gurgles when you start reaching red line, and, it's so much more responsive. It might not be perfect, but it sure has helped.
Thanks to this link on the air box t-stat ... http://www.matthewsvolvosite.com/for...pic.php?t=8830

Now for the 50.0L/100kms: I managed to check 4 other Volvo S70s, and they all do the same thing. Having checked with the other guys and my android torque app, I noticed that 50.0L/100kms is the highest number the console will display ... where in fact, the torque app registers an even higher number, as much as 360.0L/100kms on a T5 on initial acceleration, whether hard or soft. Same thing with an AWD and GLT, all S70s.

And, all cars are in great shape with no CEL lights.

So, unless somebody has something, I'm just going to have to accept the fact that, S70s are fat *** dogs rolling their bellies in city streets with all this stop and go, and getting 18 mpg in a city with a red octagon at every block, is actually pretty good.

So, as a summary, make sure your vaccum lines are clean, and, make sure your intake air and fuel is where they shoud be ... they have a huge affect on fuel economy.

Thanks lads ... have a great summer ...