Fuel consumption crashes to 5 mpg?

UKMike · Post by **UKMike** » 29 Mar 2010, 05:04

Terrific site, I appreciate the many excellent contributions. I've waded through the topics and can't find any on the problem I'm having: 1997 V70 2.5 10v with 102k miles: I have been getting 31mpg highway/ 27 city. This week I did a tankful of gas and only got 80 miles out it, ouch!

Indicated fuel consumption on the dash has remained at 27 mpg, it took 13 gallons to fill it again so probably not the fuel gauge.
I haven't noticed any difference in power, acceleration, engine sound, exhaust volume/colour. I've jacked the car up and inspected all from the tank to the injectors = no sign of leaking fuel. Also no smell of fuel or fuel on the ground under the car when parked. Also no warning lights on the dash.

The need for a new catalytic converter wouldn't make this drastic a change to consumption?

I'm stumped! Before I take it to the repair shop for some expensive detective work, I thought I'd ask the question here.

Many thanks

Post by **VCA** » 29 Mar 2010, 06:52

UKMike wrote:Terrific site, I appreciate the many excellent contributions. I've waded through the topics and can't find any on the problem I'm having: 1997 V70 2.5 10v with 102k miles: I have been getting 31mpg highway/ 27 city. This week I did a tankful of gas and only got 80 miles out it, ouch!

Indicated fuel consumption on the dash has remained at 27 mpg, it took 13 gallons to fill it again so probably not the fuel gauge.
I haven't noticed any difference in power, acceleration, engine sound, exhaust volume/colour. I've jacked the car up and inspected all from the tank to the injectors = no sign of leaking fuel. Also no smell of fuel or fuel on the ground under the car when parked. Also no warning lights on the dash.

The need for a new catalytic converter wouldn't make this drastic a change to consumption?

I'm stumped! Before I take it to the repair shop for some expensive detective work, I thought I'd ask the question here.

Many thanks

So, no stink of unburned gas after she warms up? Tends to rule out the Coolant Temperature Sensor. The fuel's obviously going somewhere--you're either burning it (know anyone who can tailpipe test it?), leaking it (you haven't seen/smelled leaking fuel?) or, someone is stealing it (does your gas filler door/cap lock?)

bguzz · Post by **bguzz** » 29 Mar 2010, 10:00

check your fuel pressure regulator. If the diaphragm is torn, you will be dumping lots of gas via your injectors. It should have a fuel smell out the tail pipe pretty much also.

If you pull the vacuum hose off the regulator and can smell gas in the hose and or regulator...that is a sure sign that you have a ruptured regulator diaphragm. It would explain this other than a major pressure leak.

Post by **jblackburn** » 29 Mar 2010, 10:42

I had a bad FPR, but I was getting about 18 mpg highway, and the/ car ran like a piece of junk. Be careful pulling off that line - gas in your eyes is not fun if it decides to squirt out of there.

Using that much gas, I'd think you'd at least have some smoke out the tailpipe.

You'd likely have thrown a engine light for the huge vacuum leak I would have suggested as a cause.

Try putting the trip computer on instantaneous MPG and watching it as you drive along. As you settle down in gear, it should show values in the 20's. It might be possible someone stole your gas...it happened to me when I had just put a full tank in my dad's Jeep I was borrowing at a time when gas was $4/gallon.

Post by **VCA** » 29 Mar 2010, 11:03

jablackburn wrote:It might be possible someone stole your gas...it happened to me when I had just put a full tank in my dad's Jeep I was borrowing at a time when gas was $4/gallon.

I'm still betting someone's taking his petrol. You would notice, at 5mpg either: raw gas smell around the car [the 960 had a slow leak at the fuel rail and I could smell it with no problem--and it wasn't enough of a leak of affect mileage], or black smoke from the tailpipe and a toasted cat. Fuel efficiency that bad without either of those two attendant symptoms strongly suggests theft.

UKMike · Post by **UKMike** » 31 Mar 2010, 10:45

Many thanks for the suggestions - I have another post in on this forum because of almost total loss of electrics in the drivers door - I had to break the plastic locking tab to the fuel cover to fuel up. So looks like while I sort that out I'll chain the dogs to the car o'nite - or get Mr baseball bat to sort it out!

I'll check out the FPR as well and let you know.