fuel comsumption

[mazdamx-6ls]

my 99 sl2 used to do 300miles with a full tank of gas. recently its been only doing around 200m. it has 92k. i had the plugs and the belts replaced last year. do u think by replacing plugs and wires it will solve this? or is there anything else that i need to do?
thank you

[drew300]

Any fault codes?
Tire pressures?
PCV valve?
Dirty throttle body?
Idle Ok?
Dirty air cleaner?
Vacuum leaks?
Right grade of oil?
I guess you could pull a plug to see if they're burning ok.
I try too find a fault before I change stuff so as not to add a new fault that I'll overlook when trying to fix something.

[mazdamx-6ls]

thanks for replying
i cant see anything wrong with it.(to the naked eye)
where should I start?

[PlayStation3]

have you been driving different? and is it auto or manuel?

[mazdamx-6ls]

Originally Posted by PlayStation3

have you been driving different? and is it auto or manuel?

its an auto. well i used to drive mostly freeway mile before. now mostly city. but I still should do more than 17-18 miles a gallon. (driving economically). my 93 mx-6 V6 does the same, but this is a inline 4. I dont know where to start.

[drew300]

That bad?
Does the "SES" lamp work? (key on, engine not running)
Maybe a computer scan to see if anything is amiss.
I'd check all the things I mentioned before, and maybe add to that check the tranny fluid, for level and see if it's burnt.

[saturnspeed_12]

look into coolant temp sensor being bad. also clean the throttle body. but with mpg that low, its usually the coolant temp sensor. if your car runs at 1/4 mark, then its probably the problem. it should be running closer to 1/2. its just dumping unwanted fuel in.

the problem can also be caused by a bad map sensor.

[mazdamx-6ls]

Originally Posted by saturnspeed_12

look into coolant temp sensor being bad. also clean the throttle body. but with mpg that low, its usually the coolant temp sensor. if your car runs at 1/4 mark, then its probably the problem. it should be running closer to 1/2. its just dumping unwanted fuel in.

the problem can also be caused by a bad map sensor.

thank you for replying. as for the coolant sensor. i thought saturns (atleast sl's) were supposed to run at 1/4 coolant temp. mark. my saturn always ran at 1/4 mark and it still does from the day I bought it. (it did gas fine then) and my saturn before that, a 94, ran at 1/4 mark too. isnt that the way it was designed?

[drew300]

my '99 also runs at about 1/4, MAYBE a little higher, not near 1/2. (unless I'm stopped on the highway) Been that way since new.
A fellow at the top of the list said his cat was plugged, that would definately lower mileage, but a "SES" lamp should light for that.

[saturnspeed_12]

SES light wont come on just because a clogged cat.

now the car is suppose to run between the 1/4-1/2 mark closer to 1/2. this is near 195 degrees which is the normal for most all cars on the road.

my car never went beyond 1/4 mark when i first had it. i was pulling at the max of 38mpg. then after a while the gas mileage started to drop, and i was averaging 33mpg and figured i would replace the sensor. after doing so my temp was sitting perfect closer to 1/2 and i was back averaging 38mpg and when i played nice, would see 42+.

but never buy a plastic tipped one!!!!!!!!!!!!!!! they will be like the original, and over time will crack like the original. i was lucky mine didnt crack. but quite a few do crack and then you have to replace the connector too. only buy a good brass tipped one, which i would only go for the dealer part/ac delco part.

[drew300]

No "SES' with a clogged cat?
My '99 SW1 has 3 - O2 sensors, 1 at the manifold, 1 ahead of the cat, and 1 after the cat.
I thought the fore / aft ones would pick up a cat problem.
Am I wrong?

[saturnspeed_12]

it wont let you know its clogged. and you have 2 sensors, not 3.

[PlayStation3]

ok this might be off topic but i get 22 mpg driving hard and 25 driving like a good driver and that is all city with an mp7 tranny.possable mine be bad it reads 1/4 for most of the way untill about an hour or so

[drew300]

Hi Saturnspeed.
It's been too wet to climb under the car, but I'm 99% sure I've seen the 3 -
O2 sensors. And my '97 Astro has 4 of them, (!), for sure.

[saturnspeed_12]

because your astro van has two exhaust banks. although they could do without the other downstream.

hell 3.8 series II has two sensors yet has two banks and is obdII. they could have done three, but they put the upstream where both combine.