Rotten fuel economy on my 96' 850

sreynolds · Post by **sreynolds** » 02 Mar 2005, 21:47

I haven't found a suitable answer to my bad mileage problem anywhere and I was hoping someone could help me out here. Here's the scoop ... I have a 1996 Volvo 850 GLT (non-turbo) wagon with AT. One year ago, the mileage was 27 mpg hiway / 21 mpg city. About six months ago, the mileage dropped gradually to about 19 mpg hiway / 13 mpg city ... Terrible!! I replaced the following: air filter, spark plug wires, distributor and plugs. Also tried running sea foam and injector cleaner through the gas line/tank and vacuum ports. Cleaned out the throttle body, replaced every vacuum hose that I could find, and replaced the flame trap. The car does not show any codes even from the proprietary Volvo scanner. Okay, so here's the strangest thing yet ... my wife was driving the car and it died on her. The number 3 cylinder lost all compression, but all others were fine. I ended up replacing the engine a couple of weeks ago and didn't use any of the old engine parts. The acceleration and handling are great as usual. Guess what, I still get the same exact bad mileage as the old engine!!!!!

Volvo still maintains that there are no codes showing on their scanner after the repair??? Does anyone have even the slightest idea of what to do. I can't afford a new car right now and the fuel bills are killing me.

AJU · Post by **AJU** » 03 Mar 2005, 09:54

Make sure your brakes are not dragging

Post by **matthew1** » 03 Mar 2005, 10:48

Sounds like a bad O2 sensor, but without the code(s).

sreynolds · Post by **sreynolds** » 03 Mar 2005, 11:20

My brakes are not dragging at all and the O2 sensors did not return a code from the scanner (either Autozone's or Volvo's). I also had Volvo give the transmission a power flush with their Volvo approved equipment last week.

I am reluctant to just change O2 sensors on the unlikely event that one or two of the very expensive devices are not working correctly. Any way to verify if the sensors are good without replacing them? Also, what about the fuel filter? Can that affect mileage (or just performance)?

AJU · Post by **AJU** » 03 Mar 2005, 11:39

Fuel filter might have a minimal affect on mileage in the city when you do a lot of accelerating, but straight highway cruising you probably won't see a change at all. Any other possible sources of drag besides brakes dragging? Are your wheel bearings good? Tires up to recommended pressure? Alignment good? How's your parking brake?

Winter fuel mixtures will cause a drop of about 10% in gas mileage, but yours is excessive. I would try and rule out the simpler, cheaper things before replacing O2 sensors myself, and if you have gone 6 months without a code for a bad O2, I doubt it is that.

Try disconnecting you battery for about 15 minutes (negative side) to reset adaptives and see if you notice any change in the mileage, if so then it may well be a sensor. Is your car running rich?

sreynolds · Post by **sreynolds** » 03 Mar 2005, 14:11

My parking brake is okay, tires okay, car coasts well when put into neutral. Over the weekend, I disconnected the battery for an hour and it made no difference. Transmission shifts well and the lockup solenoids were checked by Volvo - all okay.

The exhaust doesn't smell like gasoline, but it does have a kinda strong combustion smell (like an older model car). Are there any other pollution controls that could have this dramatic effect on mileage? How about exhaust obstructions? And, if the injectors are leaky (won't hold pressure after the car is shut off), will that affect mileage? The old engine would not hold pressure after shut down, but I haven't checked the new one with new injectors.

Tsquared · Post by **Tsquared** » 03 Mar 2005, 15:41

Have an exhaust shop check the flow of the cat. If it is clogging that could cause poor mileage - not sure if it would trip the computer or not.

Guest · Post by **Guest** » 04 Mar 2005, 10:28

Don't think I'm crazy. Did you change tire size before the drop? If so the diameter of the tire may be smaller, causing the odometer to read incorrectly.
Just a thought, as it seems you've check alot of other obvious causes.

Da' Moose · Post by **Da' Moose** » 04 Mar 2005, 21:52

One can test a converter in two ways. #1 flow test, #2 Temperature of the converter

I have tested flow with my handy dandy drill. Drill a small hole (1/8

tylka · Post by **tylka** » 05 Mar 2005, 11:04

Definitly check the converter, but also the O2 sensors can be checked by a shop that has a diognostic tool that reads the motor while it is running. I had mine checked and the car never did show a code for the sensor, but the sensor was reading low signals. The tool was made my Snap-On and it was pretty much a laptop that showed the engine stats. As you know a bad O2 sensor can lead to other problems like a bad cat. converter and probably more. Hope you find the problem soon. Good luck.