gas guzzler

[MiNoahsPinkMartini]

I'm concerned... and not so mechanically inclined. My car just recently started eating through alot of gas. Does anyone have any ideas what might be causing this? It's a 88gl with 33000 miles on it and it's never given me any real problems. I just figured I'd ask here before, so when I take it into the shop and they start spewin problems at me, i'll know whats true and whats not! I kinda look like sucker most of the time! It's a blonde thing...

Thanks for your help!

[dave valiant]

Have you tried the basic tuneup stuff?My Brat's mileage was way down before I did plugs,wires,cap,rotor,fuel filter,and air filter.After I did all that my mileage went back to normal.Give it a shot if you haven't done it already.

[c150L]

I too was thinking the general tune up things first. Also, I believe a worn out or disconnected O2 sensor would cause an engine to run rich, use more gas. My 88 wagon went from 27.5 avg mpg all the way doen to the mid teens before I noticed that the fuel ppump had rusted out and was pumping half my gas on the road as I was driving. Was noticed dripping while idling in a parking lot. (Smaller, but getting bigger wet spot on ground in front of RR wheel.) Tried some fixes on the engine and milage continued getting worse. Engine was still working on 27 mpg, but the gas applied directly to the pavement did nothing toward improving gas milage.

[raceman77]

a bad O2 sensor will cause this,l`ve seen it a million.Check the sensor wiring first though.Has anyone worked on your car lately?With any semi-modern electronic fuel injected car showing sudden excessive fuel consuption my first guess is faulty O2 sensor/circuit.A fuel leak could do it too and that should be easy to spot if you`re looking....good luck with it..

[calebz]

Mine has been getting about 15mpg lately.. after testing everything that was testable and coming up with nothing.. I slapped in another MAF that was laying around.. problems seem to have gone away

[Stupidru]

Dave, what mpg are you getting now?

[oddcomp]

i wonder if this saab maf i have would work.. hmmm

[dave valiant]

I am currently getting any where between 19-22MPG.I'm sure it would be better if my trip to work wasn't almost all uphill.When I go to the Midwest Meet I'm hoping to be in the 25 MPG range since South Dakota east of the Black Hills is so flat.

[Fuji Fellow]

RE: The O2 sensor affecting MPG. Yes, a bad O2 sensor can certainly cause a rich running condition. The O2 sensors in this generation of cars were single-wire sensors, which don't use an external heater as in many other OBDII systems. They depend purely on the 2200-degree heat from the exhaust stream to start working properly, and this doesn't happen until the engine's been running for several minutes. (For this reason most early generation ECM's will operate in Closed Loop mode, ie, ignoring most of the feedback inputs, until the engine reaches operating temperature.)

 

But I digress... point being, it's a pretty good practice to replace the O2 sensor generally whenever you replace spark plugs. They both operate in much the same environment, are built about the same, and will wear about the same. As was mentioned in a previous post, double check the wiring from the sensor as it routes up around the transaxle, to where it enters the wiring harness. Make sure the wire isn't frayed, and that the connections are clean and tight. The O2 sensor develops a small voltage, in the 1-volt range, which the ECM must be able to ACCURATELY receive, in order for it to process the signal properly.

 

After you've checked the signal wire from the O2 sensor itself, NEXT check the ground return connections. In single-wire sensors, ground return is made from the exhaust pipe, up through the engine block, then to the transaxle, and finally from a heavy ground wire that goes from the car body to either the transaxle or the engine block (usually the transaxle on our Soobs). Make sure this body-to-engine ground cable is present and clean and tight. If the ground connection is poor, then the ECM can't accurately see the proper signal that the O2 sensor is sending... often resulting in some squirrely things happening such as a mysterious bumping cutout of the engine as you run along the highway, or overly rich mixtures, etc.

 

In general, a lot of mysterious driveability gremlins can be banished by going over all hoses and electrical connections, making sure everything is clean and tight. G'luck matie

[thealleyboy]

Fuje and the others make some excellent points...

 

Not sure I agree with replacing the 02 along with the spark plugs every time. That might be overkill (and I'm pretty anal about these kinds of things!!). I would estimate the 02 would be a "replace at 100k" item, even though it's only a "check" item on the manufacturers reccomended maintenance schedule.

 

Even though the car has only 30K, a bad 02 is a good guess on a 16 year old car. But, so would lots of other things. I would go thru the 6/60 items for everything (except for timing belts) for starters, and see what that does. You may get lucky and solve the problem thru the ignition and fuel filter maintenance.

 

An 02, or other sensor, could very well be a problem, and your ECU would warn you by means of the "Check Engine" light and record this in memory. If the warning light has ever gone off, you should scan the ECU for trouble codes. Code retrieval information is available on this site. These codes will give you enough clues to get started in troubleshooting the faulty system.

 

good luck, John

[88xt6joe]

I just put plugs and a fuel filter in mine today and atleast it seems to be running much better and the idle is smoother. I'll have to check the gas milage again when I fill up.

 

Joe

[Partsman]

Fuji:

 

1. Our Subes do not have OBDII.

2. Closed loop is the term for engine management operation when the vehicle is warm and all inputs are within parameters. Open loop is what the car runs in until it is warm.

3. O2 sensors do not operate in the same environment as spark plugs - plugs get a shot of cool air and fuel every once in a while! However, that's like comparing apples and oranges, since the O2 does not have to spark every other stroke - it just handles a chemical reaction and creates current.

 

Other than that, you make several good points. My only addition is that it seems like the computer only sets a O2 sensor code if there is a wiring problem to the sensor. I'm pretty sure I have a 230k old sensor in mine, and there is no check engine light on. However, my mileage sucks, so I am going to change the sensor. In addition, I will check the ground distribution as you suggest.

[Fuji Fellow]

Fuji:

 

> Closed loop is the term for engine management operation when the vehicle is warm and all inputs are within parameters. Open loop is what the car runs in until it is warm.

 

Other than that, you make several good points. My only addition is that it seems like the computer only sets a O2 sensor code if there is a wiring problem to the sensor. I'm pretty sure I have a 230k old sensor in mine, and there is no check engine light on. However, my mileage sucks, so I am going to change the sensor. In addition, I will check the ground distribution as you suggest.

Arrgh, Partsman, sorry about getting open and closed loop modes confused. It's been a long night .

 

I was readin' about the OBDII systems, in that they are less prone to ground problems because they get their ground reference from the 4-wire cable, rather than having to hope all the ground contacts (exhaust-engine-transaxle-body) are there and intact. The article I was reading mentioned a tech who did a clutch job on a customer's car, and then the car had Check Engine light issues afterward... turns out the tech had forgotten to connect that ground cable.

 

Anyway, thanks for the correction .