Just recently noticed that I am experiencing a terrible loss of fuel economy. Have checked what I think are most of the common causes. Plugs, wires are good. No vacuum leaks that I can find. Temp sensor seems to be working. It's as if overnight my fuel mileage went to pot. I used to get about 300 miles per tank and now it's as if overnight I'm down to 250 miles per tank. Probably would help if I told you that it's a 740 Wagon with the Regina system and 170,000 miles. Any ideas out there? And yes, I have checked to see if there is fuel running out on the ground and there isn't.

 

i'd first check exactly the mileage you get--sometimes the mind plays tricks... fill it up to the top, check the odo, drive 100-200 miles, top it off, check the miles driven, divide.

 

Has it suddenly cot colder there? I would look at the coolant temp sensor for the ECU, not the gauge one, there are two different ones.
All EFI systems are very sensitive to coolant temp inputs.
But as Ted said above, check and verify first.

Regards, Andrew.

 

Is your exhaust emission darker? I'm thinking you need to replace your O2 sensor. Thats a classic cause for drop in gas mileage but not a noticeable change in how the car runs. Temp sensors when they go bad tend to make the car run odd.

 

make sure there isn't any gas in the vacuum line that connects to the fuel pressure regulator.

 

O2 sensors fail slowly over thousands of miles. They will cause reduced mileage, but not suddenly.

Regards, Andrew.

 

Air filters affect mileage, but usually it's a gradual degradation not sudden. Anyway I would have a look in the air box.

 

Thank you all for your replies. Exhaust doesn't seem any richer or darker. Checked for bypassing pressure regulator, dirty air filter, etc. Also checked what we thought was temp sender for ecu, but must have been gauge sender. Where is ecu temp sender located? We checked the sender on driver's side of block.