Decrease In Gas Mileage

I have a 1997 Saturn SL1 w/118,000 miles. For the last two years I have been averaging 32.5 mpg. In the last few weeks my average mpg has decreased to 27 mpg. This drastic decrease bothers me. Does anyone have any ideas?

I have recently (within last 12 months) replaced the PCV valve spark plugs and wires, fuel filter, and air filter. In the last month the only things I have done are replace the water pump, replace transmission fluid/filter, oil change, tire balance & alignment, and new front passenger tie rod.

Please help as gas prices continue to shoot through the roof.

changed driving habits/more city driving/shorter trips/ less highway?

has the ECT ever been replaced? a bad ECT(which saturns are known for) can have a HUGE effect on gas mileage. i've known a few people that the ECT paid for itself in 2 tankfuls(extreme cases, but still). the ECT was redesigned a few years back and last much longer now.

besure that the PCV valve is the OEM peice, not aftermarket. - http://files.automotiveforums.com/gallery/showphoto.php?photo=26072

be sure the spark plugs are not platium plugs.
replace the ECT sensor with the new brass design from the saturn dealership($15)

Driving habits, routes, etc. have not changed. For 18months I have only been driving highway to and from work....no where else.

I am going to change the ECT this weekend and see what happens. Thanks for the advice.

What is the issue with the platinum plugs and the aftermarket PCV valve?

Thanks Again.

need a how-to for the ECT?

lots of manufactiors have issued TSBs on platium plugs, i don't know all the reasons, but the big one for saturns is that oil destorys the electrodes, and we burn alot of it.

non-OEM PCVs tend to be universal for several different brands(to save costs), PVCs have certain flow rates, and the aftermarket ones never get it right. this causes bad emissions and oil burning.

Lucky for me my saturn does half a quart burned between changes -- Not bad for 193,812 miles now

I have a how-to for the ECT from Wolfman, but I have heard a few people having problems with that method. Another recommendation would be great just to compare.

Thanks for the info on the plugs & pvc. I have not had an oil burning issue as I have heard discussed on this forum. Maybe I have been lucky.

We'll see how the replacement goes this weekend. Also, I bought the ECT from Saturn of Mobile (Alabama) yesterday and the total cost, with tax, was about $19.

Well, I changed the ECT today. The entire job took less than 15 minutes. I followed wolfmans how-to and also jacked up the drivers side so that the trans. fluid would maybe not leak out. In all, I lost about 2-4 oz. of trans. fluid...not bad at all.

Thanks for all your help. I guess time will tell if my gas mileage increases.

at first glance it does not appear my gas mileage has increased....will see after a few more days/weeks

in a few days/one week, fill your tank full, record the mileage or set the trip odometer. at your next fill up after that. record how many gallons it took and the difference in miles. divide the miles by the gallions. let us know what you get.

BTW, how is the air filter?

I will let you know the mpg when I fill up this week. I check my mpg every tank and is why I knew of the problem. I can tell already that my mpg hasn't improved b/c i know about how many miles i should get at each quarter tank marking.

Air filter is good. New plugs & wires. New water pump. Could water pump installation be a problem?

the water pump itself, no. there is a small chance if the thermostat was bad and overcooling the engine, same thing as a bad ECT. block too cold, PCM goes rich to warm it up, dumps more fuel in. watch how long it takes the engine to warm up, and where the gauge normally is(just a hair below 1/2 is about normal).

the ECT was the old style right?(different tips) did you check the connector too?(in a few cases, the ECT cracks to the point the coolent gunks up the connector).

also check all the intake tubing, make sure no little mice have made a nest or anything.

at this point i'm still not ruleing out the possiblity the hard start is related.

etherway, the ECT is the easy thing because it fixes the problem 95% of the time. that other 5% we are getting into is the hard part. if i could, i would like to plug in a scantool, an igntion scope and a 5-gas machine, but i have a feeling you don't want to drive up to chicago...so lets try something else, do you have access to a multimeter/voltmeter/ohmmeter? does your state do emission testing? how old are the coil packs?

my thought is for a clean running enigne you need fuel, oxygen(air), spark, and compression. you defintly have fuel(maybe too much), air we don't know, spark we don't know, compression we don't know(but not as likely as the others). i'm thinking more about spark right now...

quick check: pull the spark plug wires off the coil packs, check for corrision on the towers, if there is, a little sandpaper should clean them up, besure the wires go back on in order(left to right, on the block, 1 - 2 - 3 - 4, on the coils, 4 - 1 - 2 - 3) you should feel i little click when the wire is on all the way. also check the bolts on the module under the coils for corrision.

actually, the ECT appeared to be the new style. I will post a picture of the old when I can. I noticed no cracks and the connector appeared clean. The temp guage (before and after ECT replacement) is as you said, just below half.

As far as intake tubing. I removed the intake from the filter to the engine and it was clear.

I do have a multimeter available at my office. Alabama does not do emission testing or any testing/inspections for that matter.

I have to check the coil packs, etc.

Thanks for the continued assistance.

Additionally, I filled the tank today. 243 miles driven, 8.8 miles driven.....27.6 mpg. Not near the 32.5 mpg from three weeks ago.

with your multimeter, check the resistance of each spark plug wire. and from tower to tower on each coil(8Kohms ideal for wires, replace if over 12K ohms, for the coil 8k - 15k ohms), then with the engine running, do a voltage drop test from the grounding bolt on the DIS module to neg termial of the battery(any more then 0.5 volts needs serviced.

also, stupid thing... check tire pressure. when was the last oil change. are you absolutey sure there was nothing done 3 weeks ago that could change anything(even something that seem unrelated?)

Everything that has been done in the last month or so is listed in my very first post. I will do all of the other checks Sunday.

Last oil change was about 1500 miles/6 weeks ago.

im in this vocational class at the votec center here in virginiabeach, and im only 17, but my instructor has said that gas mileage can be decreased my many reason, it all depends how you drive, so i would try to put a bigger air filter in for more airflow, or change your air/fuel ratio. sorry if this doesnt help

if you were looking for a long term change above stock MPG, yes. but in this case it is a sudden drop in MPG.