First off, thanks for a great forum....been very helpful, but this one has me stumped.

I bought a 95 SL1 SOHC, AUTO w/ 178000 miles about a month ago. Right out of the gate without doing a thing, it was a 34mpg car with my driving habits. This was great as my wife and I drive 155 miles roundtrip everyday and ride together for work. Car has run great from day one. Starts easy, drives smooth, shifts relatively smooth...

All of the sudden, I am getting NO MORE than 19mpg. Habits and routes have not changed. In trying to replace everything I could think of, I did the following....

1, New plugs (old ones looked fine. Nice, clean, light brown color)
2. New plug wires.
3. New O2 Sensor
4. Oil and filter change
5. New air filter
6. New fuel filter
7. Chevron TECHRON injector cleaner TWICE
8. Transmission filter and oil change.
9. 2 New Tires On the Front. All tires inflated to max.
10. Car uses about 1.0-1.5 qts every 800-1000 miles
10. Scanned at dealer for codes. None stored none found. Dealer said all sensors are operating in normal range. I am a bit skeptical of this because when I pull the BRAND NEW PLUGS and BRAND NEW 02 SENSOR are black soot covered. I would think something would be out of whack computer wise?
9. If I "stomp it" to pass on interstate or get up to speed, it blows a decent size black cloud.

With all that said, the car has NOT CHANGED how it runs. Starts great, runs great, shifts pretty good. Just a massive loss of Fuel Economy. I have looked HIGH AND LOW for a gas leak and none exist. AGAIN, the car runs fine. I have always had a bit of a jerk/miss in the 40-60mph range, but its hardly noticeable. Temperature gauge seems to work accurately and I dont have any overheating issues.

So, why does my Saturn, that runs the same as the day I bought it (near flawless) , suck so much gas all the sudden? Literrally, I went to bed the 33mpg man and woke up the 19mpg man. And, no, my gas isnt being stolen...LOL.

I am ready to sell this car and move on but I kind of like it and I really loved it when it was 33mpg....as frame of reference...i Bought the car a month ago and this issue started about 10 days ago....tried all of the above after mpg reduction. What did I miss? Is the engine shot? What gives? Help me o wise ones!

Thanks!

 

Possibly a plugged catalytic converter, but it sounds like your engine temperature sensor may be cracked, which can cause the engine to dump too much fuel when not needed giving a rich condition as well. This will not normally set any engine codes. It's a $18 part, and a 13mm deep socket and about 10 minutes of time to replace. There are 2 sensors, 1 for the computer, 1 for the gauge. The gauge one has 1 wire, the computer one has 2 (Which is usually below the gauge one). Could also cause your miss in the 40-60 range.

Please let us know if you find the problem.

 

+1
sounds like classic ECTS issue (if the ECTS is the original from the factory) -- which you won't know until you pull it to check it. Replace with brass design.

Be sure to replace connector as well -- corrosion here is a killer. (Dealer only part)

Would be an ironic failure of the ECTS (timewise) but it is possible. These usually fail much earlier in life.

Which (brand) 02 sensor did you use as a replacement?

If the ECTS replacement doesn't do it for you, check fuel pressure at the schrader port under the hood. Though if the fuel pressure was too high, I would expect it to directly affect performance....

 

derf and iq...thanks for the timely response. picked up the sensor this AM and will try it tonight. will post my findings. I really hope this solves it. I was in hog heaven for a few weeks....paid 900 bucks for it and it needed nothing. Picked up some nice front seats for it on ebay for 10 bucks for the pair and we had a really nice, economic car.....until this. Its so bad, we drove our grand cherokee to work today at 16mpg..YUK! Hopefully this gets it..I will post findings.

 

[QUOTE=bandkindy]
its a BOSCH O2 sensor/

 

well, unfortunately, I pulled the ECTS and it was the brass deisgn. Replaced it with a new brass design just to be safe. No change, crappy gas mileage (17-19mpg), slight miss around 50-60mph....

any other ideas at all? CAT? Anyone?

 

Did you start buying gas from a different station?

Was the previous owner running regular oil or synthetic? And are you running the same as they were?

Have you noticed a marked increase in oil consumption?

I didn't see EGR cleaning in your above posts. Usually you would expect more obvious performance issues but it's worth pulling and checking for deposits (which sounds like a given if there is buildup on the plugs and 02 sensor.

Also -- remember that as soon as the O2 sensor gets coated, it may lose its ability to send proper feedback to the PCM -- if it is coated with crap, it will see no oxygen and tell the system to run richer......

At what rpm does it idle?

 

gas at the same gas station....during my trials and tribs, I tried others

idles about 1000. very little fluctuation and smooth

yes...its consuming more oil about 20% more

when i got the car, i put synthetic oil in it, not sure what was there before.

nothing done with egr, but thought like you....no other marked performance issues....

derf...thanks for your help. could this be a cat issue. thinking back, I remember hearing something sounding like a muffler dragging. Look under right away and nothing dragging...could this possibly be a cat convertor issue? wouldnt I have more obvious symptoms?

 

Catcon issues usually end up either clogged choking off the engine or not passing emissions. Have you considered the fuel pressure regulator being punctured and allowing extra gas at all engine rpms? There's the fuel input, output, and vacuum. Checking to be sure the vacuum side of the diaphragm isn't punctured and filled with gas and having gas in the vacuum lines may be causing the fuel mileage drop. The last check would be the idle air control valve possibly sticking as the engine should be idling around 800-900 rpm. Removing and cleaning with electronic contact cleaner may help unstick the servo motors pushing/pulling the valve. While you're at it clean the throttle body passages and linkages to free them of build-up. The slight miss may be from corroded coils and wirebrushing the bare metal and boltsthat contacts the frame through the mounting bolts and coating them with dielectric grease will prevent further corrosion and good electrical conductivity. The metal-to-metal contact provides ground for the coils. Sand off the towers lightly and coat them also with dielectric greaseand at the plug end.

 

problem solved...LOL. I SOLD THE DARN THING. I will be posting a question on a how to on the 96 SW I bought to replace this basket case.....thanks for all your help anyway!